Chapter 13. Second- and Third-Trimester Pregnancy

Over the last 30 years, ultrasound has played an essential role in the care of the obstetric patient. The body of knowledge and expertise in obstetric sonography is now enormous. Ultrasound is the primary imaging modality for evaluation of uterine, cervical, and amniotic fluid abnormalities; placental and umbilical cord problems; and determination of gestational age, fetal congenital abnormalities, multiple gestation, and fetal presentation.1 While some of these applications are of limited relevance in the emergency setting, certain information can be rapidly obtained with bedside ultrasound that is potentially critical to the emergency care of an obstetric patient.

This chapter discusses the use of emergency ultrasound to evaluate pregnant patients in the second and third trimesters. During this time period, the major indications for its use are the initial assessment of the pregnant trauma patient, evaluation of vaginal bleeding and preterm labor, and evaluation of abdominal pain. Emphasis will be placed on a focused or goal-directed ultrasound examination to rapidly measure fetal cardiac activity, estimate gestational age, and exclude placenta previa. Additional applications include assessment of amniotic fluid volume, cervical length and fetal position, and the evaluation of nonobstetrical causes of abdominal pain.

Confirming the presence of an intrauterine pregnancy when symptoms arise in the first trimester is now considered a standard application of emergency ultrasound. The clinical indications for performing the examination, the limited information sought, and the recommended technique are all widely agreed upon and well described. In contrast, the role of emergency ultrasound in the second and third trimesters of pregnancy is not well established. Yet, emergency physicians are frequently faced with evaluating women in the latter part of pregnancy. Pregnant women may present to the emergency department because of trauma, profuse vaginal bleeding, or severe abdominal pain. Depending on the practice setting, obstetrical consultation may not be rapidly available and patients may have had no prior prenatal care. Increasingly, ultrasound is immediately available in the emergency setting and clinicians are adept at its use. Clearly, there are a number of clinical situations during the second and third trimesters of pregnancy where a rapid, goal-directed ultrasound examination can both expedite diagnosis and improve the overall care of mother and fetus.

A discussion of the use of emergency ultrasound in the second and third trimesters of pregnancy must begin by addressing the following questions:

1. What are the standard clinical indications for emergency ultrasound in the second and third trimesters of pregnancy? In what clinical situations should emergency ultrasound be routinely employed?

2. What focused ultrasound applications are reasonable uses for the clinician?

3. For the major clinical indications, what are the goals of the ultrasound examination?

4. Are there alternative imaging modalities to ultrasound that should be considered?

What are the standard clinical indications for emergency ultrasound in the second and third trimesters of pregnancy? The concept that emergency ultrasound should remain focused, or goal-directed, helps define its appropriate use in the latter part of pregnancy. In this setting, the focused concept takes on particular importance for the following reasons. First of all, because the scope and quantity of information potentially available through ultrasound in late pregnancy is enormous, the physician performing ultrasound in the emergency setting must have a distinct, clinically relevant scanning goal in mind before placing the probe on the abdomen. It would be inappropriate, for example, to assess fetal cardiac morphology in the emergency department. Similarly, the idea of performing a screening ultrasound examination on a clinically stable patient with established pregnancy, simply to confirm gestational age or fetal well-being, may not be an appropriate indication for emergency ultrasound. Even in the hands of obstetric ultrasound specialists, the impact of screening ultrasound on perinatal outcome remains debatable.2 Second, the medicolegal ramifications of basing clinical decisions on emergency ultrasound in the obstetric patient mandate caution. In one analysis of malpractice claims involving diagnostic ultrasound, obstetric ultrasound constituted 75% of the cases.3 Not only should the information sought with each application be carefully limited, but ultrasound should be used only for emergency indications where the immediate benefit of the information outweighs the possibility of a missed diagnosis.

Major clinical indications for the use of emergency ultrasound that seem to satisfy these constraints include the initial evaluation of a pregnant trauma patient, mid- and late-trimester vaginal bleeding, preterm labor, and abdominal pain of unclear etiology in a pregnant patient.

What focused ultrasound applications are reasonable uses for the clinician? Several standard emergency ultrasound applications are indicated in late pregnancy and are considered safe and accurate in this setting. These include the focused assessment with sonography for trauma (FAST) examination to exclude hemoperitoneum, a right upper quadrant ultrasound examination to assess for gallstones and signs of cholecystitis, and a renal ultrasound examination to evaluate for severe hydronephrosis. In addition, the following focused applications are unique to the obstetric setting. Ultrasound may be used to rapidly visualize fetal cardiac activity. The fetal heart rate can be measured using M-mode scanning. In the second and third trimesters, gestational age may be estimated by measuring biparietal diameter or femur length. Transabdominal scanning can be used to evaluate for possible placental abruption, to exclude placenta previa, to assess amniotic fluid volume, and to ascertain the position of the fetus. Transvaginal or translabial scanning may be used to clarify the relationship of the placenta to the internal os and to measure cervical length.

For the major clinical indications, what are the goals of the ultrasound examination? In other words, given the patient's clinical problem, what clinically important question(s) can be answered rapidly with a focused ultrasound examination? For example, in a trauma patient who is comatose and appears to be possibly pregnant, the following questions could be answered with emergency ultrasound: Is the patient pregnant? Is there evidence of free intraperitoneal fluid (from hemoperitoneum or uterine rupture)? Is the fetus alive? What is the gestational age of the fetus (and might it survive in the extrauterine environment)? Is there obvious retroplacental hematoma? Figure 13-1 presents a goal-directed approach to emergency ultrasound in the second or third trimester of pregnancy based on the patient's clinical problem.

Are there alternative imaging modalities to ultrasound that should be considered? The emergence of ultrasound as the main imaging modality in pregnancy is based in part on its being considered extremely safe for the fetus. Human organogenesis largely takes place before the 10th week of gestation, when diagnostic ultrasound is often used. The absence of an association between ultrasound and fetal structural anomalies supports its safety in early pregnancy.4 The critical period of brain development is during the 14th to 22nd week of gestation. The theoretical adverse affect of ultrasound on the fetal brain, due to production of thermal energy and cavitation, has been the topic of several important epidemiologic studies, all of which have found no deleterious effects on cognitive development.1, 5, 6 By contrast, the risk to the fetus associated with exposure to ionizing radiation, particularly from abdominal computed tomography (CT), is considered significant.

For assessment of fetal well-being, alternatives to sonography include the handheld Doppler stethoscope for measurement of fetal heart tones and cardiotocography to continuously monitor fetal heart rate and uterine activity. Cardiotocography is a form of fetal assessment that simultaneously records fetal heart rate, fetal movements, and uterine contractions to investigate hypoxia. Cardiotocography is a sensitive, although indirect, test for the diagnosis of placental abruption after trauma, and remains the cornerstone of that evaluation. In the absence of a reliable menstrual history, a very rough estimate of gestational age can be obtained by measuring fundal height. This crude test represents the only alternative to sonography for estimating the age of the fetus if the history is not available.

For the evaluation of vaginal bleeding in late pregnancy, sonography has supplanted the traditional double setup examination as a means of excluding placenta previa. Placental abruption is usually diagnosed on clinical grounds, with the assistance of cardiotocography. Use of magnetic resonance imaging has been described in the work-up of relatively stable patients with unexplained vaginal bleeding, but it has not been widely adopted.7

Ultrasound frequently plays a complimentary role to the physical examination and cardiotocography in the evaluation and management of preterm or precipitous labor. Ultrasound is the only imaging modality used in this setting to assess cervical length, amniotic fluid volume, and fetal position.

Abdominal pain of unclear etiology is the single major clinical indication for use of emergency ultrasound in late pregnancy where alternative imaging modalities—such as plain radiography, CT, and pyelography—are commonly employed in the nonpregnant patient.

The clinical indications for performing emergency ultrasound in the second and third trimesters of pregnancy are

• trauma,
• vaginal bleeding,
• premature labor, and
• abdominal pain.

Trauma occurs in 6% of pregnant patients8 and is a leading cause of nonobstetrical mortality.9 Furthermore, fetal loss as a result of trauma far exceeds maternal mortality.10 Emergency ultrasound has the potential to play a critical role in the initial evaluation of obstetrical trauma. Use of the FAST examination to evaluate maternal intra-abdominal hemorrhage has been shown to be beneficial.11 Because fetal well-being is dependent on adequate maternal circulation, a tenant of trauma care is that resuscitation of the mother and assessment of maternal injuries is the initial priority. Besides maternal shock, processes that contribute to fetal loss include direct fetal injury, uterine rupture, placental abruption, ruptured membranes, and premature labor. Of these, placental abruption is the most common and may occur after relatively minor trauma and in the absence of other injuries.12 While cardiotocography and observation for the occurrence of frequent contractions remain the cornerstone of the evaluation,8 ultrasound may rapidly confirm the presence of significant abruption, usually in the setting of a high clinical suspicion.12 In addition, and perhaps more importantly, emergency ultrasound may be used to rapidly demonstrate fetal cardiac activity and determine gestational age.11

Fetal Cardiac Activity in Trauma

Fetal assessment begins with measurement of fetal cardiac activity to establish fetal viability. This step is recommended early, not only in evaluation of the pregnant trauma patient,12 but in patients with vaginal bleeding13 and preterm labor as well.14 The normal fetal heart rate following the first trimester is 120–160 beats per minute. Sustained bradycardia is associated with fetal hypoxia and acidemia. Historically, in emergency medicine, fetal cardiac activity was established by measuring fetal heart tones with a handheld Doppler stethoscope.

Bedside ultrasound is an attractive alternative to the handheld Doppler stethoscope for initial detection of fetal cardiac activity. Using B-mode scanning of the gravid uterus, locating the fetal heart and assessing the presence of cardiac motion is relatively straightforward. Using M-mode scanning, the waveform produced by cardiac motion can be recorded. Fetal heart rate is then determined rapidly and accurately with the aid of obstetrics software, contained in most ultrasound machines. In the setting of significant trauma, assessment of fetal cardiac activity can be done as an adjunct to the FAST examination. Furthermore, sonography should be used to confirm fetal cardiac activity whenever cardiotocography is not immediately available, or if a fetal heart rate signal cannot be detected by the Doppler probe on this device.8

Estimation of Gestational Age in Trauma

Knowledge of gestational age is critical in this setting since decisions need to be made for emergency cesarean section, such as in the setting of maternal cardiac arrest.15 In a stable trauma patient, gestational age may influence the decision to proceed to exploratory laparotomy.11 In addition, the gestational age and fetal maturity influence the management of placenta previa, preterm labor, rupture of membranes, eclampsia, and other severe medical illnesses in late pregnancy. In the setting of trauma, sonographic assessment of gestational age, along with fetal heart rate, can be performed as an adjunct to the initial FAST examination.

When assessing gestational age, the following general points should be borne in mind. By current convention, obstetric dating begins with the first day of the last normal menstrual period, referred to as gestational age or menstrual age, and is equal to the fetal or conceptual age plus 14 days. Fetal viability should be assumed when the gestational age is greater than 24 weeks. The pregnancy is considered term at 38 weeks. Sonographic estimates of gestational age are progressively less accurate (less predictive validity) the later in pregnancy they are obtained, due to increasing variation in biological size of the fetus (Table 13-1). A simple rule that reinforces this principle is that the variability (2 SD from the mean) of a gestational age estimate is equal to approximately 8% of the predicted age.16 An ultrasound measurement of biparietal diameter that yields a gestational age of 32 weeks has a variability of ±19 days. Nevertheless, estimates based on biparietal diameter, obtained as late as 20 weeks, still outperform menstrual history for predicting onset of labor.17 If possible, gestational age should be based on results of a formal ultrasound examination performed prior to 20 weeks, or on a reliable menstrual history. Beyond 20 weeks, use of emergency ultrasound to estimate gestational age may be necessary if there has been no prenatal care, menstrual dates seem unreliable, or when the mother has an altered mental status.

In the first trimester, crown-rump length is the preferred biometric measurement for establishing gestational age. In the second and third trimesters, measurements that are commonly used and well validated to estimate gestational age include biparietal diameter (BPD), head circumference (HC), and femur length (FL). Modern ultrasound machines generally come equipped with software that will automatically calculate gestational age based on any one of these parameters. In choosing which biometric parameter to measure, the established predictive validity of the parameter (Table 13-1) should be considered, and the ease and speed with which it can be obtained. A parameter that has excellent predictive validity according to the obstetric literature, but is difficult to measure and therefore prone to error, may not be well suited to the emergency setting.

In the second trimester, BPD and HC are the most widely used measurements.16, 18 Although in expert hands, HC has a somewhat better predictive validity than BPD, measurement of BPD is preferable in the emergency setting because of the relative ease and, therefore, accuracy with which it is obtained. While HC must be calculated in a particular plane, BPD can be measured in any plane, provided the line of measurement intersects the thalamus and third ventricle.16, 19 Of particular relevance to the emergency setting is a study that directly correlated neonatal survival in premature infants with various biometric measurements obtained by ultrasound shortly before birth. Based on analysis of receiver operator curves, a BPD of greater than 54 mm was the single best predictor of survival.20

In the third trimester, FL is a frequently used alternative to BPD for estimating gestational age.16, 21 In late pregnancy, measurement of BPD may be difficult because the fetal skull is frequently located within the maternal pelvis and obscured by acoustic shadowing. The predictive validity of FL is slightly better than BPD at this stage.18 Femur length is relatively easy to measure because the transducer need only be parallel to the femoral long axis.16, 22

In late third trimester, identification of ossified epiphyses around the knee represents a potentially very rapid means of estimating gestational age, and is therefore attractive in the emergency setting. Appearance of the distal femoral epiphyseal ossification center indicates a gestational age of 29 weeks or greater, whereas its absence means that the gestational age is less than 34 weeks.23 Similarly, appearance of an ossified proximal tibial epiphysis suggests a gestational age of at least 35 weeks and that the fetus is at or very near term.16

Abruption from Trauma

The term placental abruption refers to the separation of a normally implanted placenta from the uterus prior to the birth of the fetus. Any significant trauma occurring beyond the first trimester may potentially result in placental abruption, but particular attention must be given to victims of motor vehicle crashes, falls from height, and domestic violence.8, 24, 25 When trauma results in major maternal injuries, the reported incidence of abruption is as high as 35%.

Abruption requiring emergent delivery is possible even when the maternal physical examination is normal.12 A heightened index of suspicion is made even more critical, given the variable and sometimes subtle presentation of abruption. While the classic presentation is the triad of vaginal bleeding, uterine tenderness, and labor, patients may manifest few, if any, signs or symptoms early in their course. The evaluation may be further complicated by the presence of distracting injuries, drawing attention away from early clues to the diagnosis. Finally, abruption is a dynamic process demanding close observation and ongoing monitoring for fetal–maternal effects. A trauma-induced abruption may be self-limited or continue to evolve up to 24 hours after the inciting event.8

The diagnosis of abruption following trauma remains largely clinical, beginning with a meticulous search for evidence of vaginal bleeding, uterine tenderness, labor or fetal distress, the latter being the key to diagnosis. Uterine contractions are present in nearly all cases of abruption although they may be difficult to appreciate by either the physician or patient. Contractions are characteristically of high frequency but low amplitude. Pearlman et al. demonstrated that 6 hours of cardiotocographic monitoring after trauma was 100% sensitive for predicting all subsequent complications.12 A similar study confirmed that even rare cases of late-onset abruption or fetal distress after trauma were heralded in each instance by early abnormalities on cardiotocography.25 Hence, an absence of signs of uterine irritability or fetal distress remains an excellent indicator of maternal–placental well-being, suggesting that abruption is either absent or clinically insignificant. Cardiotocography should be a routine part of the initial evaluation of every pregnant trauma patient, even those who are asymptomatic. The stable patient without evidence of uterine irritability for 6 hours may be discharged home with appropriate follow-up and instructions. If the patient demonstrates any degree of uterine irritability during the 6-hour observation period, it is recommend that monitoring be continued for 24 hours.

As stated above, the role of ultrasound in the pregnant trauma patient remains first and foremost the assessment of free intraperitoneal fluid, fetal viability, and gestational age. Ultrasound has a limited role in the diagnosis and management of placental abruption. Fewer than 50% of sonographic studies are positive in the setting of known abruption.26 While it is reasonable to include a rapid assessment of the placenta as part of the FAST examination, one must interpret the findings in the context of other supporting evidence for abruption. Given the poor sensitivity and specificity of sonography for abruption, any result that contradicts other clinical or cardiotocographic evidence for or against abruption must be viewed with skepticism. One scenario where the diagnostic utility of ultrasound is enhanced is that of the pregnant trauma patient with vaginal bleeding originating from the cervix, where the main considerations are placenta previa or abruption. In this setting, ultrasound can effectively diagnose abruption by excluding previa as the cause of the bleeding.27

Several laboratory markers are available to assist in the evaluation of potential abruption. Coagulation tests indirectly implicate abruption by showing evidence of fibrinolysis and disseminated intravascular coagulation. These markers, however, are neither specific nor sensitive for the diagnosis of abruption. The Kleihauer–Betke test, which assesses the presence of fetal hemoglobin in the maternal circulation, has been suggested as another screening test for abruption because, on average, abruption causes 15 mL of fetal blood to be mixed into the maternal circulation. Drawbacks of this test include the long processing time and general lack of prognostic value.28 Multiple studies have shown the Kleihauer–Betke test to be of little clinical value in the overall management of placental abruption.8, 28

Uterine Rupture

Uterine rupture is a rare complication of blunt trauma in pregnancy, occurring in only about 0.6% of cases,8 and is much more common as a complication of labor. Traumatic uterine rupture usually results from a high-energy mechanism. Uterine rupture invariably results in fetal demise; accompanying maternal mortality is approximately 10%.8 Traumatic uterine rupture is likely to be diagnosed by emergency ultrasound during the initial FAST examination or while attempting to establish fetal viability.11

During labor, uterine rupture and uterine dehiscence usually occur at the site of a previous uterine incision, such as for cesarean section or myomectomy. Uterine rupture is defined as complete disruption of the fetal membranes, causing communication between the uterine and peritoneal cavities, and usually involves extensive tearing of the uterine scar and severe hemorrhage.29 The clinical presentation of uterine rupture is variable, but often dramatic. It may include pain described as “tearing,” vaginal hemorrhage, maternal shock, and loss of station of the fetus. Uterine dehiscence, by definition, leaves the uterine serosa and fetal membranes intact. It often involves only a small rent in an old myometrial scar and may cause only minor additional symptoms during labor. The overall incidence of uterine rupture and dehiscence is approximately 0.05% of pregnancies, rising to 0.8% of those involving labor after prior cesarean section.29

Vaginal bleeding beyond 20 weeks' gestation complicates 5% of pregnancies. It is caused by placental abruption 13% of the time and by placenta previa 7% of the time.30, 31 Placenta previa and abruption account for the vast majority of cases requiring transfusion or cesarean section, as opposed to the approximately 80% of vaginal bleeding cases that are due to early labor, lower genital lesions or remain undiagnosed. Overall, vaginal bleeding in the second and third trimesters is associated with fetal mortality or adverse outcome in nearly one third of all cases.32–34

Placenta Previa

In placenta previa, the placenta is implanted in the lower pole of the uterus instead of high up in the fundus; it is located either over or very near the internal os. Placenta previa has traditionally been subdivided into complete, meaning that the entire os is covered by placenta, and partial, meaning that, when dilated, the os is partially covered. This distinction, however, is usually irrelevant to the sonographic evaluation prior to the onset of labor.

Placenta previa is present at term in only approximately 0.5% of pregnancies. Yet, routine ultrasound in early second trimester has found low-lying placenta in up to 45% of patients and an apparent placenta previa in 5%.35–37 This paradox is widely referred to as placental migration. In fact, it is due not to reimplantation of the placenta at a more superior location on the uterus, but rather to the relatively rapid elongation of the lower uterine segment, effectively drawing the placenta away from the os.24

Maternal risk factors for placenta previa include advanced age, multiparity, non-Caucasian race, previous cesarean section, and prior history of placenta previa.24 Placenta previa usually presents as painless vaginal bleeding. However, pain from contractions sometimes accompanies the hemorrhage. The first episode of bleeding typically occurs in the third trimester, but may not occur until after the 36th week in up to one third of cases.24

The evaluation of possible placenta previa begins with transabdominal scanning since it is rapid, noninvasive, and reliable in locating a non–low-lying placenta. Also, a digital vaginal examination can precipitate severe hemorrhage in the presence of placenta previa. Ultrasound can be used to locate the placenta and exclude placenta previa prior to vaginal examination, obviating the traditional “double set-up” examination. Because its sensitivity for diagnosing placenta previa is 92%–98%,38, 39 a placenta seen to be located at or near the fundus by transabdominal ultrasound effectively excludes previa. After excluding the diagnosis of placenta previa, the clinician can then proceed to evaluate the patient for placental abruption. On the other hand, if the placenta is clearly seen to cover the entire os, particularly in the third trimester, the diagnosis of placenta previa is generally confirmed. However, when the placenta appears on transabdominal ultrasound to be low lying or partially covering the os, or if an adequate view cannot be obtained, further evaluation with transvaginal or translabial scanning is generally indicated. With the transabdominal approach, the relationship of the inferior edge of the cervix to the internal os is frequently obscured by patient obesity, an overdistended bladder, myometrial contractions, a posterior placenta, or the ossified fetal skull.40, 41 In one study of patients with suspected previa, assessment of the placenta–os relationship was impossible in 31% of transabdominal scans.42 Diagnosis of placenta previa by transabdominal scanning has a high false-positive rate, up to 17% in one large study.43 Nevertheless, in the case of severe hemorrhage, if findings on transabdominal ultrasound appear consistent with previa, the patient should proceed directly to the operating room. A double setup examination may then be performed in the operating room at the obstetrician's discretion.

Transvaginal sonography is a widely accepted modality for further evaluation of possible placenta previa when transabdominal scanning reveals a low-lying placenta or is nondiagnostic.24, 30 Since the late 1980s, numerous studies have documented that it is safe and more accurate than transabdominal scanning.38, 43–46 Optimal imaging is usually obtained with the endovaginal probe no closer than 3 cm to the cervix,42 and there have been no reported cases of the procedure precipitating or worsening hemorrhage. In all but one study, sensitivity for the diagnosis of placenta previa has been 100%, where an internal os–placenta distance of less than 2 cm is taken as positive. Transvaginal scanning is able to image the internal os–placenta relationship and eliminates the majority of false-positive transabdominal scans.43 In a study that is particularly relevant to the emergency setting, Oppenheimer et al. demonstrated that when the distance from the placenta edge to the internal os was greater than 2 cm, vaginal delivery was possible in every case. Cesarean section for vaginal bleeding was required in 7 of 8 cases in which the distance was less than or equal to 2 cm.44 Transvaginal scanning also has the technical advantage over transabdominal scanning that the bladder need not be fully distended.

Translabial, or transperineal, sonography is an increasingly accepted alternative to transvaginal scanning.24, 47 As with transvaginal scanning, the os-placenta relationship is almost always well visualized, thereby clarifying the findings of transabdominal scanning40, 48 and a full bladder is not required. The advantages of translabial scanning over transvaginal scanning are that it is noninvasive, theoretically safer, and does not require an endovaginal probe. Translabial scanning can be performed immediately after an apparently positive or nondiagnostic transabdominal scan without changing probes. It therefore may be particularly well suited to the emergency setting

The approach to management of placenta previa depends largely on the sonographic assessment of fetal well-being and gestational age. Although cesarean section is the definitive treatment, vaginal bleeding due to confirmed placenta previa is frequently managed in an expectant fashion. The rationale for expectant management are (1) bleeding prior to the third trimester is often self-limited and can be treated by transfusion, if necessary; (2) vaginal bleeding represents little direct risk to the fetus in the absence of significant abruption or maternal shock; and (3) delaying delivery, to maximize fetal maturity, improves perinatal outcome.24 Obviously, confirmation of fetal well-being is a prerequisite to expectant management. A rapid initial measurement of fetal cardiac activity can be performed in the emergency setting with transabdominal ultrasound, although cardiotocography is then required for ongoing fetal monitoring. Other measures of fetal well-being, such as amniotic fluid volume and biophysical profile, also may have an impact on management.

A determination of gestational age also is required to guide treatment decisions.13 The following general guidelines have been proposed with regard to management of previa based on gestational age. When gestational age is less than 24 weeks, delivery is indicated only for hemorrhage that is life threatening to the mother. Between 24 and 34 weeks, fetal distress and life-threatening hemorrhage are indications for delivery. Beyond 34–37 weeks, delivery is indicated for significant bleeding or labor.24

Placental Abruption

Any abnormal separation of the placenta occurring after 20 weeks' gestation is defined as a placental abruption. Prior to this date, placental separation is considered part of the overall process of spontaneous abortion. While it affects less than 1% of all pregnancies, abruption accounts for more than a quarter of all perinatal mortality.13, 24 The epidemiology of placental abruption suggests a variety of risk factors contribute to its development, many of which relate to more general microvascular disease. One of the strongest associations is with maternal hypertension, both chronic and pregnancy-induced.49 Cigarette smoking and cocaine abuse have also been linked to higher rates of abruption.50, 51 Trauma is an uncommon but important cause of abruption.

Hemorrhage begins at the point of separation between the placenta and the uterus, or the placenta and the amnion. The timing and degree of subsequent bleeding from the cervix is dependent on the size of the hemorrhage and its location relative to the placenta. The amount of vaginal bleeding is not a reliable guide to the degree of placental abruption or the severity of hemorrhage. In 20% of cases, patients may experience no vaginal bleeding despite significant placental separation. The amount of vaginal bleeding must never be taken as a guide to degree of internal hemorrhage. Similarly, the presence of abdominal pain, considered a hallmark symptom for abruption, will be absent in nearly half of all cases.13, 24 It follows, therefore, that any evaluation of painless vaginal bleeding in pregnancy must consider the possibility of abruption.12, 24, 29 The most consistent finding in abruption will be the presence of uterine irritability and contractions.12 These may be unappreciated by both patient and physician without the aid of cardiotocography.

Because neither the character of the bleeding nor the presence of pain can be relied upon to differentiate placental abruption from previa, it is recommended that the evaluation of vaginal bleeding in the second and third trimesters always begin with an ultrasound examination to exclude placenta previa. Once previa is excluded sonographically, abruption becomes the major diagnostic consideration. The diagnosis of abruption is usually made clinically, rather than with imaging, and rests on cardiotocographic findings of uterine irritability and fetal distress. While ultrasound will show evidence of placental hemorrhage in up to 50% of cases, it lacks sufficient sensitivity and specificity to serve as a reliable diagnostic standard. Use of magnetic resonance imaging has been described in the work-up of relatively stable patients with unexplained vaginal bleeding, but it has not been widely adopted.7

Once diagnosed, immediate Cesarean section remains the definitive treatment for placental abruption. Decisions regarding the manner and timing of any intervention will necessarily reflect an overall assessment of maternal–fetal well-being. If the fetus is immature and the abruption is judged to be mild, an expectant approach may be attempted. Signs of preterm labor may be difficult to distinguish from mild abruption.24 If there is no evidence of fetal distress, a cautious trial of tocolytic or magnesium therapy may be considered. Evidence suggests that such pregnancies can be successfully prolonged without serious consequence to the fetus. A term fetus or evidence of uterine irritability refractory to tocolytic therapy should prompt expedited delivery. Similarly, fetal distress or maternal signs of abruption indicate a need for immediate cesarean section.24, 30

Approximately 7% of newborns are premature at birth, resulting in both mental and physical impairment.52 Preterm labor is defined as regular uterine contractions accompanied by characteristic changes in the cervix, occurring prior to 37 weeks' gestation. The main goal of the emergency evaluation of preterm labor is assessment of the potential for premature delivery. Ultrasound plays a pivotal role in this setting, as it is a safe, rapid, and accurate method of imaging the cervix for signs of labor. In addition, ultrasound may be used to estimate gestational age and confirm the presence of a fetal heart rate. Fetal well-being may be further assessed sonographically through the biophysical profile and measurement of amniotic fluid volume. Amniotic fluid volume and biophysical profile are of potential utility in the setting of any severe maternal illness, when expectant management versus active management depends on fetal well-being. Finally, when the clinician is faced with a patient in active labor, ultrasound can be invaluable in rapidly identifying fetal lie, or the presence of multiple gestations.

Cervical Effacement

The primary indication for assessing the cervix in late pregnancy is to confirm the onset of labor in the setting of regular contractions prior to 37 weeks. As labor begins, the cervix undergoes effacement followed by dilation. While the digital examination has traditionally been used to evaluate such cervical change, ultrasound has emerged as a safer, more accurate means to do so.53 Sonographic measurement of cervical length represents an objective way to quantify effacement.

There are several justifications for using an ultrasound examination rather than the digital examination in this setting. First, a direct contraindication to digital examination may exist, such as placenta previa or ruptured membranes. Digital examination in these settings can produce life-threatening bleeding or chorioamnionitis, respectively. A transabdominal or translabial ultrasound examination obviates the need for an invasive examination. Second, an ultrasound examination has been shown in numerous studies to be more accurate than digital examination in estimating cervical length and predicting preterm labor, in part because the anterior–superior portion of the cervix is located beneath the bladder, inaccessible to the examining finger.53 Funneling (dilatation of the internal os) occurs when amniotic contents begin to protrude into the cervical canal and is one of the earliest signs of labor. Because the internal os cannot be palpated manually, this sign is assessed strictly by sonography.53–57

There are three methods for imaging the cervix with ultrasound: transabdominal, transvaginal, and translabial (transperineal). The transabdominal and the translabial approaches have the advantage of being noninvasive. The transabdominal approach is the least reliable, successfully imaging the cervix in only 46% of patients without, and 86% with, a full bladder.58 Presenting fetal parts and a large maternal habitus may obscure the cervix. The transvaginal technique produces the most consistent findings, touted to result in visualization of the cervix in up to 100% of patients.54 The limitation of this technique lies in its invasive nature and need for an endocavitary probe. It carries a theoretical risk of chorioamnionitis if rupture of membranes has occurred. Translabial (or transperineal) ultrasound is considered the most technically difficult method. In the hands of a skilled sonographer, however, this approach provides an adequate view of the cervix in up to 95% of patients.54, 59 In the emergency setting, a reasonable approach is to begin with transabdominal scanning and proceed to translabial scanning with the same probe if the cervix is poorly visualized.

From studies involving all three techniques, it has become clear that cervical measurements can predict the risk of preterm delivery. In a seminal study of nearly 3,000 women at 24–28 weeks' gestation, Iams et al. demonstrated a positive correlation between short cervical length (<30 mm) and risk for preterm birth before 35 weeks55 (Figure 13-2). Another study of patients between 16 and 28 weeks' gestation found a 79% rate of preterm delivery in those with cervical funneling of greater than 50%.60 Subsequent studies have confirmed the predictive value of both short cervical length and the presence of funneling, and have extended the findings to twin pregnancies.54, 57, 61 For the most part, subjects in these studies were asymptomatic outpatient patients, limiting applicability to the emergency setting. Moreover, the impact of such findings on clinical management, such as the need for cervical cerclage, remains uncertain.

Using ultrasound to determine the presence or absence of cervical changes can help the emergency physician risk stratify patients with symptoms suggestive of labor. The critical cervical length appears to be 30 mm; preterm delivery becomes likely when less than 30 mm. Cervical sonography should be used in conjunction with clinical variables—such as results of the biophysical profile, gestational age, and history of preterm births—to influence management decisions. The goal of such an evaluation is to identify patients who would benefit from admission and tocolysis versus candidates for outpatient follow-up. The utility of cervical sonography in preterm labor was retrospectively evaluated at one facility. Women were hospitalized only if they had a cervical length less than 30 mm. This protocol produced a decrease in hospital days of 48% without affecting the rate of preterm births.62

Fetal Position and Number

Lie refers to the relationship of the fetus to the long axis of the uterus while presentation describes what fetal part is nearest the cervix. In normal deliveries the fetal lie is longitudinal and the presentation is cephalic. Transverse lie and breech presentation—where the fetal sacrum or feet, respectively, are engaged in the pelvis—are referred to as malpresentations. The classification of breech presentations is presented in Figure 13-3.

In the emergency setting, it is absolutely essential to know the presenting fetal part. Even with good prenatal care, fetal presentation is often unknown because prior to 25 weeks the fetus frequently changes position. Breech presentations, which account for some 3%–4% of all deliveries, are fraught with complications such as asphyxia, cord prolapse, and spinal cord injuries to the fetus.63 Knowledge of the presentation allows the emergency physician to mobilize the appropriate equipment and support staff needed for delivery. In an emergency vaginal delivery, the presenting part is discovered easily by physical examination of the vagina or perineum. Prior to this point, determining fetal position by palpation may be difficult, particularly for a nonobstetrician. Moreover, when preterm labor is accompanied by vaginal bleeding or premature rupture of membranes, vaginal examination is contraindicated. In such cases, an ultrasound examination can be used to establish fetal position.

As important as the fetal position is determination of the number of fetuses. Ultrasound is invaluable in identifying the “surprise twin” prior to labor and delivery.64, 65 Perinatal death occurs seven times more frequently in twin deliveries as compared to singletons.66 Like breech presentations, delivery of twins requires additional expertise, support, and equipment.

Amniotic Fluid Volume

Besides providing a perfect acoustic window for the sonographer, amniotic fluid serves multiple functions for the developing fetus. It cushions, regulates temperature, helps prevent infection, and provides fluid and nutrients to the developing embryo. Late in pregnancy, the main source of amniotic fluid is the kidney. Thus, a normal amount of amniotic fluid is considered a sign of at least one functioning kidney. Fetal swallowing and intramembranous absorption are the main sources of elimination.67, 68

In addition to being an important, measurable component of the biophysical profile, amniotic fluid volume is often used by itself to monitor maternal–fetal well-being. Alterations in amniotic fluid volume have been found to correlate with numerous maternal and fetal problems. Hence, some familiarity with amniotic fluid volume measurement is essential for the emergency sonographer. Like the full biophysical profile, measurement of amniotic fluid volume is most likely to be done in the emergency setting when sonographic indicators of maternal–fetal health might influence the course of management.

A number of semi-quantitative methods for assessing amniotic fluid volume by ultrasound have been proposed. Amniotic fluid index is considered by many investigators to be the most accurate measurement technique, but also the most time-consuming. It is also the most widely used by many obstetricians. For a more rapid assessment, either the largest vertical pocket or the two-diameter pocket techniques can be used. Compared to the largest vertical pocket, the two-diameter pocket technique is more sensitive in detecting oligohydramnios. In the case of multiple gestations, the largest vertical pocket may be superior in quantifying amniotic fluid volume associated with each fetus.68, 69 In the emergency setting, any one of these techniques is reasonable and the choice will depend on the clinician's experience.

Although its significance is controversial, oligohydramnios is defined as less than 300 mL of amniotic fluid volume and can be divided into acute and chronic presentations. Acute oligohydramnios is usually due to premature rupture of membranes. The emergency provider should be aware that in these patients, a low amniotic fluid volume is associated with a shorter latency time from rupture to delivery.68 Chronic oligohydramnios is commonly associated with postdate pregnancies, as the fetus outgrows the placenta. Uteroplacental insufficiency, often from maternal hypertension or autoimmune disorders, causes shunting of blood away from the kidneys toward more vital organs such as the brain. This results in oligohydramnios. Common fetal anomalies, pulmonary hypoplasia, low Apgar scores, and need for cesarean section have all been associated with oligohydramnios. Despite these associations, many investigators have found no correlation with fetal morbidity or mortality.67, 68 Present in up to 1.7% of pregnancies, polyhydramnios (>2,000 mL) is usually found at prenatal evaluation of a “large-for-dates” pregnancy. Polyhydramnios can also be divided into acute and chronic presentations. The acute form usually occurs in the second trimester and is found when the mother or fetus is very ill. Chronic presentations outnumber acute presentations 50 to 1, and can be divided into maternal (15%), fetal (13%), and unknown (67%) causes. The most common maternal cause is glucose intolerance, which leads to fetal macrosomia. Other causes are infection (syphilis, rubella, cytomegalovirus, toxoplasmosis, and parvovirus) and fetal central nervous system and gastrointestinal malformations. For the obstetrician, polyhydramnios prompts a more thorough work-up, including amniocentesis for chromosome analysis, antibody screening, glucose screening, and the drawing of TORCH [Toxoplasmosis, Other (Syphilis), Rubella, Cytomegalovirus, Herpes Simplex] titers.68 In the emergency setting, chronic polyhydramnios is of little significance in an otherwise well-appearing patient.68

Biophysical Profile

There are multiple noninvasive measures by which to evaluate the health of the unborn child. Traditionally, non-stress testing and amniotic fluid volume measurement have been used. The biophysical profile is a more sophisticated instrument that combines nonstress testing and amniotic fluid volume with three additional sonographic parameters—fetal tone, movement, and breathing—to derive an objective score that reflects overall fetal well-being (Table 13-2).69, 71, 72 The idea behind the biophysical profile is that the central nervous system, which is very sensitive to hypoxia, controls all of the measured parameters. Thus, a low biophysical profile score may indicate either acute or chronic fetal hypoxia.73, 74 Results of the biophysical profile are always considered together with gestational age and maternal and fetal comorbidities, but in general, lower scores have increased risk of fetal hypoxia, and scores above 8 are considered normal.72–79

Abdominal pain arising in the second and third trimesters of pregnancy represents a significant challenge for the clinician. Besides the usual complement of etiologies, obstetrical causes of pain must be added to the list. The impact of any diagnostic or management decisions on both mother and fetus must also be weighed. The anatomic and physiologic changes of pregnancy may alter the traditional presentation of many disorders. The symptomatology of pregnancy itself may overlap with that of early abdominal pathology. Concerns over ionizing radiation or medication teratogenicity may limit choices of diagnostic imaging or therapy. All of these elements conspire to confuse the clinical picture, delay definitive diagnosis, and alter therapy, which risk higher morbidity for both mother and fetus. Ultrasound offers the safest and most effective means of deciphering these complex anatomic and pathophysiologic relationships.

Nonobstetrical causes of abdominal pain in pregnancy occur at rates similar to that of the nonpregnant population. Similarly, the need for urgent abdominal surgery appears to parallel that of the general population, once ectopic pregnancy and cesarian section are excluded.80, 81 However, the morbidity associated with virtually every abdominal emergency remains higher in the pregnant patient due in large part to the challenge of early diagnosis.82

The evaluation of abdominal pain in the second and third trimesters demands maintaining a broad differential and an awareness of the altered presentation of various abdominal disorders common to the emergency setting. Table 13-3 lists the more common obstetrical and nonobstetrical causes of abdominal pain, including several extrauterine etiologies specific to pregnancy. Every work-up begins with a careful history and physical examination that should significantly narrow the differential. Laboratory tests must be interpreted in the context of pregnancy-induced changes (e.g., leukocytosis and relative anemia) and are frequently of limited diagnostic value.

Sonography is the next diagnostic step in most cases and stands to substantially narrow the differential diagnosis, if not confirm the diagnosis. As an example, right upper quadrant pain in the third trimester engenders a broad differential that should include biliary disease, pyelonephritis, nephrolithiasis, appendicitis, and liver disorders. Normal laboratory tests and urinalysis would quickly reduce the list of likely possibilities to gallstone-related and appendicitis (although up to 15% of patients with renal colic may present without hematuria). Ultrasound would then be used to confirm or exclude both of these disorders while providing additional information on the pregnancy itself.

Ultrasound is the traditional first-line imaging modality for abdominal pain in pregnancy because it offers excellent anatomic and functional information about the mother and fetus without exposing either to the effects of ionizing radiation. Intrauterine exposure to radiation may have both oncogenic and teratogenic effects. Case-controlled studies of childhood cancer show a slight but significant increase in relative risk among the children of female radiologists exposed to 1,000 mrems of radiation.81 Potential for teratogenicity and carcinogenesis appear to be greatest in the period of 2–15 weeks and decreases proportionally as the fetus nears term. In the first trimester, in utero radiation exposure is graded as low, moderate, and high as a function of total dose, with the clearest evidence for harm above a threshold level of 150 mGy (Table 13-4).83 Significant variability exists, however, depending on gestational age, body habitus, and type of study. Exposure in the second and third trimesters is less critical with an estimated relative increase in cancer risk of 64% per rad (10 mGy), which corresponds to a 0.05% relative increase in rate of childhood malignancies. Fortunately, the majority of abdominal radiographic tests fall well below these threshold levels and plain radiography and CT remain viable diagnostic tools in the gravid patient with abdominal pain.83 That said, the decision to use radiography in the pregnant patient must take into account a number of competing elements: the risk of radiation to the developing fetus, the risk of delayed diagnosis if available imaging techniques are not used, and the relative suitability of alternative imaging or management strategies. There are also the intangible concerns of mother and physician about radiation exposure that, while not supported by data, nevertheless push toward alternative imaging. The use of diagnostic radiography in the pregnant patient is often appropriate provided the risks and benefits are weighed in a manner that ensures the best outcome for the mother and fetus. Nevertheless, ultrasound assumes a position of primacy in the evaluation of the pregnant patient with abdominal pain, given its safety and unique ability to assess fetal well-being.

As pregnancy advances into the second and third trimesters, a number of anatomic and physiologic changes occur. These changes in turn alter the way a variety of common disease processes may present. The primary sonographic approach to these disorders must change accordingly. As the uterus develops, the intestinal tract is displaced upward, backward, and to the sides. Correspondingly, the appendix moves to the right upper quadrant and away from the omentum (Figure 13-4). Increased intra-abdominal pressure leads to increased esophageal reflux while the gravid uterus compresses the ureters, vena cava, and bladder.80, 81 The pregnant woman commonly experiences varying degrees of anorexia, nausea, vomiting, and back and flank pain, which are all related to the compressive and postural effects of the gravid uterus. These same symptoms, likely to be dismissed as “normal,” may in fact herald a serious intra-abdominal process. Alternative presentations, masked signs and symptoms, and distorted anatomy all serve to prevent timely diagnosis and treatment in the pregnant patient.

Obstetrical Causes of Abdominal Pain

The primary obstetrical causes of abdominal pain in the second and third trimesters are preterm labor, placental abruption, and chorioamnionitis.80–85 Preterm labor can often be diagnosed by history alone with its characteristic periodicity and crescendo–decrescendo pain. It is important to remember that while preterm labor is usually idiopathic, it may be in response to any general abdominal or systemic disorder. The diagnosis is confirmed with tocodynamometry. Ultrasound may play an important role in determining gestational age, fetal position, state of the cervix, and fetal well-being, all of which will help define patient management. Similar to preterm labor, mild placental abruption may present only with signs of early labor. Contractions are typically high frequency but low amplitude. Vaginal bleeding is common but may be absent in 20% of cases. Pain and tenderness range from mild to severe, crampy to constant, but also will be absent in over half of all patients. Ultrasound lacks sufficient sensitivity to confirm or exclude the diagnosis of abruption. Diagnosis and management decisions are based largely on clinical information in conjunction with cardiotocography. Chorioamnionitis refers to an infection of the amniotic fluid, typically following a rupture of membranes, or rarely as a complication of diagnostic amniocentesis. In rare cases, infection may occur without membrane rupture causing pain, preterm labor, and systemic signs of infection. Diagnosis can be made by ultrasound-guided amniocentesis.80–85

There are several disorders unique to pregnancy that may cause abdominal pain in rare situations. Severe pregnancy-induced hypertension is complicated by the HELLP syndrome in 5–10% of cases, which is characterized by hemolysis, low platelets, and elevations in liver function tests. Midepigastric or right upper quadrant pain may be present in 25% of cases. Spontaneous liver or spleen subcapsular hematomas can also develop, usually, but not always, in association with pregnancy-induced hypertension. Patients may experience right or left upper quadrant pain, mild coagulopathy but normal liver function tests. Hematoma rupture results in diffuse peritonitis and hemorrhagic shock. The diagnosis is often difficult since early this condition may resemble uterine rupture or abruption. Ultrasound can be useful in differentiating these conditions.81, 86

Appendicitis

Appendicitis is the most common surgical emergency in pregnancy, accounting for two thirds of all laparotomies.86, 87 In the first half of pregnancy, the clinical presentation of appendicitis remains similar to that of nonpregnant patients. Thereafter, the clinical picture becomes more atypical.87 As mentioned above, early constitutional symptoms are often subtle or dismissed as pregnancy-related. The abdominal pain is predominantly right-sided and corresponds to the right upper quadrant location of the appendix. Leukocytosis is a common but inconsistent finding and 20% of patients demonstrate a sterile pyuria. The differential diagnosis includes ovarian torsion, ovarian mass or cyst, and other sources of right upper quadrant pain, specifically cholecystitis, pyelonephritis, or hepatitis.80, 81, 88

Once suspected on clinical grounds, the diagnosis may be confirmed by graded compression ultrasound, reported to be highly accurate for the diagnosis of appendicitis during pregnancy. In one study of 45 pregnant women, graded compression ultrasound demonstrated a sensitivity of 100% and specificity of 96% for the diagnosis of appendicitis.89 However, earlier studies found a considerably lower sensitivity of 75–89%, although with similar specificities.90, 91 These results, along with its well-established diagnostic performance in nonpregnant patients, would suggest that ultrasound for appendicitis in pregnancy should be regarded as a diagnostic test that is specific, but of limited sensitivity. A negative ultrasound examination in the setting of an intermediate or high pretest probability would demand further testing.

The sonographic evaluation of appendicitis is challenging and highly operator dependent. During pregnancy, this assessment is further complicated by the upward and outward displacement of the appendix by the growing uterus. A graded compression test is performed with additional attention paid to overall appendiceal diameter, wall thickening or the presence of surrounding fluid and debris. The specific sonographic findings of appendicitis are discussed in Chapter 8. In the third trimester, the sheer size of the uterus may preclude adequate visualization, despite a proper high-lateral approach.89 Placing the patient in the left lateral decubitus position may resolve this obstacle.

As an alternative, abdominal CT may be considered. Although increasingly common in the evaluation of nonpregnant patients with suspected appendicitis, there are no studies describing its reliability during pregnancy. Concerns over fetal radiation exposure make any large comparison studies unlikely. Finally, laparoscopy or laparotomy may be indicated. It has been recommended that surgeons maintain a lower threshold for surgical exploration in the setting of pregnancy and possible appendicitis, given the variability of clinical signs and the increased morbidity associated with diagnostic delay. Negative exploration rates as high as 40% in the third trimester are commonplace and considered acceptable.91 The functional absence of the omentum in pregnancy means that a ruptured appendix is less likely to be walled off, resulting in earlier peritonitis. Perinatal mortality rises from 4.8% in unperforated appendicitis to 27.8% when the appendix ruptures.87

Cholelithiasis and Cholecystitis

Acute gallbladder disease appears to be slightly more common in pregnancy than in the nongravid population, which is a fact that reflects a higher prevalence of gallstones in fertile women (3.5–11%).92, 93 Signs and symptoms are essentially the same as the general population: abrupt onset of stabbing or colicky right upper quadrant abdominal pain accompanied by nausea and vomiting. While the presence of fever and a Murphy's sign suggest acute cholecystitis, mild elevations in the white blood cell count, amylase, and alkaline phosphatase can be normal during pregnancy. The differential diagnosis includes appendicitis, pyelonephritis, nephrolithiasis, and rare entities such as the HELLP syndrome or subcapsular hematoma. The pregnant patient with right upper quadrant pain should invariably undergo imaging tests to secure the diagnosis.

As in the nonpregnant population, sonography is the imaging modality of choice; its technique and diagnostic performance are essentially unaltered by pregnancy. Oral cholecystograms and HIDA scans are effective but less attractive options in the pregnant patient due to the attendant risks of radiation exposure. Ultrasound will identify virtually all gallstones.93 The presence of gallbladder wall thickening or pericholecystic fluid is a strong sonographic indicator of gallbladder inflammation. Most patients with acute cholecystitis can be managed conservatively with IV hydration, analgesia, and antibiotics. The risk of fetal loss with cholecystectomy approaches 5% but appears to be lowest when performed in the second trimester. However, surgery must not be delayed if the patient becomes toxic or develops pancreatitis since the fetal loss rate may reach 50% in such cases.93

Urinary Tract Disorders

The anatomy and physiology of the urinary tract are altered in pregnancy, affecting both the incidence of urinary tract infections and the sonographic appearance of the collecting system. The unifying theory appears to be increased urinary stasis due to mechanical pressure on the bladder and ureters, incomplete emptying of the bladder, and progesterone-induced relaxation of ureteral peristalsis.94 Because of the compressive effects of the gravid uterus, asymptomatic dilatation of one or more of the collecting systems may be seen in 41%–93% of patients.95 The right ureter is often slightly more dilated than the left. This obstructive effect may occur at as early as 15–20 weeks' gestation and persist throughout pregnancy. By 6 weeks postpartum, the collecting systems have reverted to normaly.95

Because of increased stasis, the incidence of urinary tract infection rises during pregnancy. This affects between 1% and 2% of all pregnant women. Pregnant women with cystitis complain of urinary urgency and frequency and suprapubic discomfort, all symptoms common to pregnancy without infection. Dysuria is less often encountered in normal pregnancy and is perhaps a more specific indicator of lower tract infections. If undiscovered, a third of cases of cystitis may progress to pyelonephritis, which present with typical symptoms of fever, chills, nausea, vomiting, and flank pain. Diagnosis is based on the clinical picture together with urine demonstrating an infection. Pyuria is present in 20% of appendicitis cases, but bacteriuria will be absent.85, 94

Despite the higher incidence of urinary stasis and infection, there is no apparent increased risk of nephrolithiasis during pregnancy. Patients present with the usual abrupt onset of unilateral flank pain, nausea, and hematuria. It is estimated that up to 15% of nephrolithiasis will not exhibit hematuria, making this a challenging diagnosis.

Traditional imaging modalities such as intravenous pyelogram (IVP) and spiral CT do not lend themselves well to the pregnant patient due to concerns over ionizing radiation. Hydronephrosis revealed on sonography, normally taken as strong indirect evidence of a ureteral stone, must be interpreted cautiously. Similarly, a urinary tract infection in the setting of hydroureter should not necessarily imply infection with obstruction. On the other hand, pregnancy alone rarely causes marked ureteral distention (over 1 cm) and such a finding on the same side as the pain would strongly suggest the presence of an obstructing stone.80, 84, 95 Ultrasound may occasionally allow direct visualization of a calyceal or uretovesicular junction stone. Patient management should be directed at relief of symptoms and a meticulous search for infection and alternative causes of pain. Most patients with nephrolithiasis can be managed successfully with IV fluids and analgesia with the eventual spontaneous passage of the stone. Rarely, ureteral stenting or basket retrieval will be needed.

Acid Peptic Disease

Reflux esophagitis is a common complication of pregnancy and may mimic a number of the more serious abdominal disorders. The increased intra-abdominal pressure and compressive effects of the gravid uterus on gastric emptying make reflux symptoms pervasive during the latter stages of pregnancy. Women will complain of episodic pain in the epigastrium, nausea, vomiting, and early satiety. Changing dietary patterns, patient positioning, and adding antacid therapy may mitigate these symptoms. In contrast, peptic ulcer disease is an infrequent occurrence in pregnancy. A reduction in gastric acid secretion and intestinal motility combined with increased mucus production during pregnancy explain this phenomena.80, 84

By the 13th week, or the beginning of the second trimester, the fundus of the gravid uterus is easily palpable above the pelvic brim and, by 20 weeks, it normally reaches the level of the umbilicus. Beyond 20 weeks, the distance in centimeters from the pubic symphysis to the fundus approximates gestational age in weeks (Figure 13-5). As the uterus and developing fetus grow, the intestines are displaced posteriorly, superiorly, and toward the flanks. As a result, by the third trimester, the appendix is normally found in the right upper quadrant (Figure 13-4). The growing uterus also compresses the ureters, frequently resulting in asymptomatic hydroureter, which occurs more often on the right side.

A thorough familiarity with the anatomy of the lower uterine segment, the cervix, and surrounding pelvic structures is essential for sonographic evaluation of placenta previa and cervical length (Figure 13-6). The normal cervix is a 3–5 cm long, mouth-like structure at the uterine opening. In late pregnancy, the inner one third of the cervix, or isthmus, elongates to form the lower uterine segment. The long axis of the cervix is defined by the endocervical canal and normally it lies at a right angle to the vagina. An area of glandular tissue, which may be hypoechoic or hyperechoic, surrounds the endocervical canal. This glandular zone disappears after 31 weeks of gestation, indicative of cervical ripening, making the canal difficult to locate sonographically.54, 64 The bladder, with its echogenic wall and anechoic urine, lies anterior to the vagina and cervix. As the bladder distends, it impinges on the anterior wall of the lower uterine segment. The rectum and sacral promontory lie posterior to the cervix and lower uterus.

Understanding the sonographic appearance of placental abruption in its various forms requires familiarity with the underlying uterine and placental anatomy. The placenta is primarily a fetal organ, with its size, thickness, and texture reflecting the health and gestational age of the developing fetus. By the early phase of the second trimester, the placenta is easily visible sonographically as a homogeneous, hyperechoic rim of tissue around the gestational sac.96 The thickness of the placenta in millimeters will approximate the gestational age in weeks and rarely exceeds 4 cm.97 By the latter part of the second trimester, the relevant anatomic segments of the placenta become more established. These include (from outside in) the myometrium, decidua basalis (endometrial–placental interface), intervillous space (area of maternal–fetal exchange), chorion (membrane that envelopes the fetal vessels), and amnion (membrane that overlies the placenta, separating it from amniotic fluid) (Figure 13-7). Fetal (umbilical) vessels course within the chorion whereas maternal (endometrial) vessels are located within the decidua.

The sonographic appearance of these layers is variable. Prominent endometrial arteries and veins within the decidua may appear as hypoechoic bands of tissue separating the myometrium from the fetal placenta, which is termed the retroplacental hypoechoic complex.96 In the intervillous space, sonolucent pools of maternal blood, called villous lakes, can lend a heterogeneous appearance to this middle layer. The addition of Doppler in both of these cases may help determine the vascular nature of a sonolucent area. Lastly, the subchorionic segment may undergo cystic changes associated with fibrin deposition in up to 20% of patients. These echogenic, cyst-like lesions can grow to 1 cm in size but are of no clinical significance.96, 97 The normal occurrence of these lesions conspire to limit the specificity of the ultrasound in the evaluation of possible abruption.

A discussion of fetal anatomy and development is beyond the scope of this chapter and has limited relevance to emergency ultrasound. Fetal anatomic landmarks that must be recognized for the biparietal diameter and femur length measurements are described in the Technique and Normal Ultrasound Findings section.

Fetal Heart Rate Determination

Fetal heart rate should be determined by transabdominal scanning using a 3.5 MHz probe. The ultrasound machine should be set for simultaneously B-mode and M-mode recording and obstetrical measurements. Scan plane is unimportant, although fanning the probe in a plane transverse to the fetal spine is one method of rapidly locating the heart. The cursor on the B-mode image should be positioned over a clearly oscillating portion of the heart, such as the mitral valve, for several cycles. Once a continuous waveform is evident on the M-mode tracing at a depth corresponding to the heart, the image should be frozen. Finally, with the ultrasound machine set for fetal heart rate determination, the distance of one or two cycle lengths should be measured (depending on the ultrasound machines software) and fetal heart rate should be automatically displayed (Figure 13-8). Sonologists should avoid using pulse wave, continuous wave, or color Doppler, particularly on a first-trimester gestation, as these modalities transmit higher energy.

Sonographic Determination of Gestational Age

Biparietal Diameter

Because of its good predictive validity and relative ease of measurement, BPD is the biometric measurement of choice for estimating gestational age after 14 weeks, when it supplants crown-rump length. Determinations of gestational age during the second and third trimesters should be performed by transabdominal scanning using a 3.5–5 MHz transducer. By widely accepted convention, the BPD should be measured at the level of the third ventricle, paired thalami, quadrigeminal cistern, and cavum septi pelucidi.18, 21 Although counterintuitive, the fetal ventricles and subarachnoid space are echogenic compared to brain due to the relative prominence of the choroid plexus and pia-arachnoid matter. The junction of the hyperechoic third ventricle and quadrigeminal cistern forms an easily recognizable sonographic landmark, referred sometimes to as the arrow sign (Figure 13-9). It has been proposed that BPD be measured in any plane as long as the line of measurement crosses the thalami and the third ventricle.19 The endpoints of measurement should be either from outer edge of the near calvarial wall to the inner edge of the far wall or from the middle of the near calvarial wall to the middle of the far wall. The near and far calvarial walls should appear symmetric. Care should be taken not to include overlying soft tissue and scalp in the measurement (Figure 13-10).19

Femur Length

Beyond 26–32 weeks' gestation, FL is an alternative to BPD, and may be easier to measure. Femur length is actually a measurement of the ossified portion of the diaphysis and metaphysis only, and does not include the cartilaginous portions of the bone. The endpoints of measurement are the junction of the ossified metaphysis and the cartilaginous diaphysis at either end. The distal femoral epiphysis, a secondary ossification center, is not included. Femur length can be measured in any plane as long as it is parallel to the long axis of the bone and includes the accepted endpoints. To avoid an oblique, falsely short measurement, the plane of section should include the femoral head or greater trochanter and the distal femoral condyle, all of which are cartilaginous (Figure 13-11).22 Although not included in the FL measurement, the distal femoral and proximal tibial epiphyses should be sought, whether or not they are ossified (Figure 13-12).

Location of the Placenta

Transabdominal Approach

To exclude placenta previa, the sonographic evaluation of vaginal bleeding should begin with transabdominal scanning using a 3.5–5.0 MHz transducer. The placenta should be located and scanned in a sagittal plane to determine whether it extends into the lower uterine segment (Figure 13-13). If so, transverse and oblique scans should be performed to determine whether it is centrally or laterally located. When the placenta is low lying, measurement of the os placenta distance by transabdominal ultrasound is often difficult because the endocervical and inferior placental edge are not in the same sagittal plane.98

The bladder should be full to best visualize the lower uterine segment and internal os. However, if the placenta appears to approach the os with the bladder full, scanning should be repeated after the patient has voided. A full bladder may create a false impression of placenta previa by pushing the anterior wall of the lower uterus against the posterior wall, thereby shortening the distance between the artificially long cervix and the placenta (Figure 13-14). Myometrial contractions, which in the second trimester may not be felt by the mother, also may result in a false-positive diagnosis of previa. A myometrial thickness of greater than 2 cm is suggestive of a contraction.96 Repeat scanning in 20–30 minutes has been suggested to avoid a false-positive diagnosis of previa due to contractions; however, this option may be unrealistic in the emergency setting. In cases where the fetal presenting part obscures the region of the internal os, an attempt can be made to manually elevate the fetus by placing the patient in the Trendelenburg position and applying sustained pressure on the lower abdominal segment on either side of the midline.

Transvaginal Approach

Transvaginal or translabial sonography should be employed to clarify the internal os–placenta relationship when transabdominal scanning is nondiagnostic. The main contraindication to these techniques is ruptured or bulging membranes.96 Transvaginal ultrasound is considered safe in the setting of second and third trimester bleeding because optimal images usually are obtained with the probe inserted only about 2.5 cm beyond the introitus and no closer than 3 cm to the cervix.44, 45 Also, the angle between the probe and the cervix is usually sufficient to prevent the probe from inadvertently slipping into the cervix. The technique should be performed using a 5.0–7.5 MHz endovaginal probe covered by scanning medium and a sterile condom. The examination should begin with sagittal scanning and the probe subsequently can be rotated and its angle changed to gain a longitudinal view of the placenta and fully image its inferior edge. Care should be taken to thoroughly investigate the lateral walls of the uterus. If the inferior placental edge appears near the internal os, the os–placental distance should be measured. To do so, the endocervical canal, which appears sonographically as a faint, hyperechoic or hypoechoic line, must first be located. The internal os is assumed to be located at the junction of endocervical canal and the anterior cervical wall. The probe should be angled and rotated until the imaging plane contains both the os and the lowest part of the placenta, at which point the image should be frozen and a measurement taken (Figure 13-15).

Translabial Approach

A translabial (or transperineal) ultrasound examination is performed using a 3.5–5.0 MHz transducer to which scanning medium is applied, then a sterile cover, and finally a thin layer of sterile jelly over the cover. If available, a phased array transducer with a small footprint is preferable. The bladder should be empty. The probe should be placed over or between the labia majora, posterior to the urethra and anterior to the vaginal introitus. Scanning should be performed in a sagittal plane, with the bladder to the left on the monitor (Figures 13-16 and 13-17). Once the cervical os and placenta are visualized, the transducer should be angled laterally to image the entire surface of the cervix and lateral walls of the lower uterine segment.

When a low-lying placenta is encountered by translabial scanning, the os–placenta distance should be measured. In addition, it has been proposed that previa can be excluded by translabial scanning when a fetal part is visualized directly adjacent to the cervix or when the cervix is separated from a fetal part only by amniotic fluid without intervening placental tissue.43

Cervical Length Assessment

The three scanning approaches available for measuring cervical length—transabdominal, transvaginal, and translabial—are essentially identical to those described above for assessing placenta previa. The transabdominal approach tends to suffer from various impediments to visualizing the entire cervix, such as large maternal habitus, intervening presenting part, or a shadow from the bony pubis. A distended bladder provides an advantageous acoustic window, but may create an artificially lengthened cervix by pushing the anterior wall of the lower uterine segment against the posterior wall (Figure 13-18). If transabdominal scanning fails to provide an adequate view of the cervix, transvaginal or translabial scanning is required.

The translabial approach to measuring cervical length generally requires more experience to perform because proper image acquisition and interpretation are somewhat difficult. With the presenting part toward the left on the monitor, the imaging plane should be adjusted so that the vagina courses directly away from the transducer between the bladder and the rectum. The cervical canal is normally at a right angle to the vagina (Figure 13-19).59 In translabial scanning, rectal gas can obscure the distal cervix and the pubic symphysis may obscure the proximal cervix.54, 64 A left-side down decubitus position and partially full bladder may facilitate imaging. Translabial scanning of the cervix is particularly difficult prior to 20 weeks or with a posteriorly directed cervix.54

Regardless of the approach employed, cervical measurements are made in a sagittal plane, from internal os to external os. The first task should be to locate the endocervical canal, which may appear hypo- or hyperechoic. The internal os is located at the junction of the endocervical canal and the anterior cervical wall. To locate the external os, the anterior and posterior lips of the cervix should be visualized (Figure 13-18). The cervix is a dynamic organ, and thus should be observed for 3–5 minutes before any measurements are made.54, 64 In general, the shortest cervical length should be recorded. This measurement will provide a conservative estimate of risk of preterm delivery. The normal cervix measures between 2.9 and 5 cm in length.99 At the same time as cervical length is measured, an assessment of any cervical funneling should be made.

Fetal Position and Number

While usually straightforward, assessment of fetal number and position by bedside sonography should be performed systematically and carefully. Not only does the recognition of breech presentation or twins have important management ramifications, but also correctly interpreting sonographic images of a moving, near term fetus can be difficult. Position should be documented using the maternal bladder as the reference point.64 The presenting part should be scrutinized in multiple imaging planes to confirm cephalic or breech presentation versus transverse lie. It may be helpful to deliberately scan the fetal spine in both a long axis and transverse plane (Figure 13-20). In the case of an established breech presentation, an attempt should be made to characterize it as frank, complete, or footling breech (Figure 13-3). To avoid missing a multiple gestation, the clinician should systematically interrogate the entire uterine cavity, making sure to image the attachment of the fetal head to the fetal body in view.65

Assessment of Amniotic Fluid Volume

There are three techniques for measuring amniotic fluid volume. A 3.5–5.0 MHz sector, convex or linear transducer is recommended for making these measurements.100

To obtain an amniotic fluid index, the uterus is divided into four quadrants using the umbilicus and the linea nigra as external landmarks (Figure 13-21). Fluid should be measured vertically in each quadrant, with the transducer parallel to the maternal sagittal plane. The sum of the largest pocket measured in each quadrant should be between 5 and 20 cm. A sum value below or above this range is considered oligohydramnios or polyhydramnios, respectively. If the amniotic fluid index measures less than 8 cm, the examination should be repeated three times and the results averaged. Of note, fetal movements should not affect amniotic fluid index.96 In twin pregnancies, a separate amniotic fluid index can be calculated for each amniotic sac and the normal range is the same as for singleton gestations.101

For the largest vertical pocket technique, the single deepest pocket should be measured in the vertical plane (Figure 13-22). A value between 2 and 8 cm is considered to be normal. Both largest vertical pocket and amniotic fluid index are prone to overestimate amniotic fluid volume if the pocket measured is long but narrow (Figure 13-23).69 In the two-diameter pocket method, the single deepest pocket of fluid should be sought, but should be measured both vertically and horizontally. The product of these measurements should be between 15 and 50 cm2. Compared to the largest vertical pocket technique, this method is felt to be more sensitive and have a lower false-negative rate in detecting oligohydramnios.102

Biophysical Profile

As mentioned above, the biophysical profile involves assessment of the following five parameters, four of which are purely sonographic: amniotic fluid volume, fetal breathing, fetal movement, fetal tone, and a nonstress test. The assessment of each sonographic component is detailed in Table 13-2. In scoring the biophysical profile, each variable is assigned a maximum value of 2, giving a maximum overall score of 10. A score of 8/10 or greater is considered normal, provided the amniotic fluid volume component is normal.70, 103 Taking advantage of this scoring system, many obstetricians will eliminate the nonstress test portion because it is the most time consuming part of the assessment, requiring 30 minutes to conduct, and longer if the fetus is asleep. Eliminating the nonstress test makes the biophysical profile a fairly rapid, purely sonographic test. The nonstress test is included only if another parameter is abnormal (i.e., without it the score would be less than 8). Further modifications of biophysical profile scoring have been proposed based on the amniotic fluid volume component. For each type of amniotic fluid volume measurement, two normal criteria have been proposed: a two-diameter pocket at least 2 × 2 cm versus a two-diameter pocket 1 × 1 cm, and largest vertical pocket of at least 1 cm versus largest vertical pocket of at least 2 cm.64, 103, 104

Placenta Previa

The term placenta previa refers to a placenta that completely covers the internal cervical os. When the placental edge is located within 3 cm of the internal os, it is termed marginal placenta previa. The term low-lying placenta is useful for describing the case of a placenta located in the lower portion of the uterus in which the exact os–placenta relationship cannot be defined, or for describing an apparent placenta previa when seen in the second trimester (Figures 13-13 and 13-24).

Transabdominal scanning can exclude placenta previa when the placenta is clearly visualized in the fundus. If the placenta appears low lying by transabdominal scanning, then translabial or transvaginal scanning is often required to clarify the os–placenta relationship (see Figures 13-15 and 13-17).

Placental Abruption

During placental abruption, a hemorrhage occurs within a layer of the placenta causing separation from the adjacent uterine wall.105 This separation and hemorrhage may remain partial and self-limited or progress on to complete abruption. The clinical manifestations of abruption and its prognosis are directly determined by the extent to which placental circulation is compromised, which in turn depends on both its size and location. Hemorrhage confined to the edge of the placenta is referred to as marginal. The degree or size of placental-uterine separation is graded as mild (grade 1), partial (grade 2), or complete (grade 3) (Figure 13-25).27, 32 These categories correlate reasonably well with the clinical presentation and prognosis. Grade 1 separations are usually marginal, involve less than a few centimeters of the placental border, and are usually not clinically significant. In contrast, grade 3 abruption can be fatal to both the fetus and the mother. Abruption is further categorized by the anatomic location of the hematoma relative to the placenta: retroplacental (in the decidua basalis, between placenta and uterine wall), subchorionic (between decidua and the membranes), and preplacental (between placenta and amniotic fluid, immediately beneath the amnionic membrane) (Figure 13-7).106 These distinctions also have significant prognostic implications, but primarily for fetal outcome. While retroplacental hemorrhage of 60 mL or more carry a 50% fetal mortality rate, similar-sized subchorionic hemorrhage translate to only a 10% rate of fetal demise. Preplacental hemorrhage is often self-limited and clinically silent, with 30% detected only after delivery.32, 106 They appear sonographically as an irregular bulge along the inner border of the placenta. Rupture of these hematomas results in the classic “port-wine” staining of the amniotic fluid.

While vaginal bleeding is considered a hallmark for abruption, its overall reliability as a diagnostic indicator is poor since it depends on the anatomic location of the hemorrhage and its proximity to the edge of the placenta (Figure 13-25). Abruption in which the hemorrhage does not communicate with the external os is referred to as concealed.

The most consistent sonographic finding in abruption is hemorrhage and hematoma, the appearance of which will depend not only on its quantity and location but also on the timing of the ultrasound in relation to the onset of hemorrhage. Acute hemorrhage appears isoechoic to slightly hyperechoic relative to the highly vascular normal placenta (Figure 13-26).107, 108 This is analogous to the situation of splenic hematomas where subcapsular and intraparenchymal hemorrhage may be indistinguishable from the adjacent normal spleen. Gradually over 1–2 weeks, the hematoma becomes sonolucent and more easily distinguished from the adjacent placenta. Hence, sonograms obtained 1–2 weeks after the onset of abruption may identify sonolucent hematoma not apparent on an initial study. Isoechoic hematomas may be suspected if a portion of the placenta appears unusually thick or heterogeneous in texture. For this same reason, hematomas of abruption are occasionally mistaken for uterine leiomyomas. Another obstacle to sonographic diagnosis is that acute hemorrhage may spontaneously decompress to an adjacent area or out through the vagina, such that the amount of retroplacental blood remaining is inadequate for visualization by ultrasound examination.16, 30, 32

Cervical Changes in Labor

Labor is heralded by regular contractions associated with cervical change. Cervical change consists of effacement of the cervix followed by dilation of the external os. The degree of effacement can be quantified sonographically by assessment of cervical length and the presence or absence of funneling. As a general guideline, a cervical length of 1.5 cm and 1 cm represents 50% and 75% effacement, respectively. Funneling is a phenomena that occurs during the beginning stage of cervical effacement, where dilatation of the internal os results in protrusion of amniotic contents into the cervical canal. Funneling can be described by its appearance as the letters Y, V, and U (Figure 13-27).54 As effacement progresses, the contour of the internal os progresses from a Y-shape to a V, and then to a U. Several criteria have been established that attempt to further quantify the degree of funneling, including funnel length, width, and residual cervical length. The most often utilized value is the percentage of funneling, which is the ratio of the funnel length to total cervical length expressed as a percentage (Figure 13-28).54

Nonobstetrical Abdominal Emergencies

The ultrasound findings associated with cholecystitis, appendicitis, and renal colic are discussed in Chapters 8, 9, and 10, respectively.

Uterine Rupture

Uterine rupture is most likely to be diagnosed by ultrasound when it occurs in the setting of trauma.11, 29 Sonographic findings associated with uterine rupture include free intraperitoneal fluid, which may represent amniotic fluid or blood, and lack of fetal cardiac activity. In addition, the uterus may be empty, with the fetus discovered in the peritoneal cavity. There are numerous case reports describing the use of sonography to diagnose uterine dehiscence during labor.109, 110 Sonographic findings include a visible defect in the uterine wall, fetal membranes intact and ballooning through the uterine wall, subchorionic hematoma adjacent to scar in the lower uterine segment, and evidence of blood layering within amniotic fluid. When uterine rupture during labor is strongly suspected on clinical grounds, an ultrasound examination is discouraged, as it may delay cesarean section.15

Placenta Previa

1. Full bladder. Although it provides an acoustic window, a full bladder may create a false impression of placenta previa by pushing the anterior wall of the lower uterine segment against the posterior wall, thereby shortening the distance between the artificially long cervix and the placenta (Figure 13-14).

2. Myometrial contractions. These contractions may lead to a false-positive diagnosis of placenta previa by thickening and shortening the lower uterine wall.

3. Incomplete examination. A false-negative diagnosis may result from failure to sweep the sonographic beam across the entire lower segment, thereby overlooking placental tissue that encroaches on the lateral aspect of the internal os.

Placental Abruption

The diagnosis of abruption cannot be excluded solely by an ultrasound examination. The specificity of ultrasound is hampered by the common occurrence of prominent endometrial vessels, subchorionic cysts, and villous lakes. These are sonolucent or hyperechoic structures that may mimic the appearance of abruption but are of no clinical significance. Cardiotocographic monitoring is required for all patients when this diagnosis is considered.

Cervical Length Assessment

1. Full bladder. A full bladder may create an artificially lengthened cervix by pushing the anterior wall of the lower uterine segment against the posterior wall (Figure 13-18).

2. Pseudodilatation of the cervix. A contracting lower uterine segment can produce pseudodilatation of the cervix. This can be distinguished from true dilatation by the following findings: length of the cervix is >5 cm; the distal cervix is normal; there is thickened myometrium adjacent to the cervix; and the dilatation passes after the contraction ceases.54

3. Other pitfalls. Advanced dilatation is difficult to distinguish from total effacement. In the translabial examination, the bladder wall can be mistaken for the lower uterine segment.59

Amniotic Fluid Volume

1. Measurement errors. Measurements may be deceptive if vertically long, but very narrow pockets are present (Figure 13-23).69 This error may be avoided by using the two-diameter pocket method. Excessive pressure on the maternal abdomen may result in falsely low measurements of fluid depth.

2. Improper gain settings. Measuring a pocket containing mainly umbilical cord should be avoided. This can look like fluid, particularly when the gain is low or in an obese patient. Adjusting the gain upward or using Doppler may help identify the cord, particularly in an obese patient.

Gestational Age Estimate

The main pitfalls for gestational age estimation are failure to carefully follow the guidelines for measurement; failure to recognize the inherent variability of estimates; and measurement of femur length in an oblique plane relative to the long axis of the bone, which may result in a falsely short measurement.

Case 1

Patient Presentation

A 31-year-old woman, who appeared to have a near-term pregnancy, presented to the emergency department after a high-speed motor vehicle crash. In the field, the paramedics had intubated the patient, obtained intravenous access, and reported a thready pulse. En route to the hospital, however, the woman became pulseless and cardiopulmonary resuscitation (CPR) with endotracheal intubation was initiated by the paramedics.

The physical examination revealed diminished breath sounds on the right lung field with ventilations, jugular venous distention, and tracheal deviation to the left. Femoral pulses were palpable only with chest compressions. There was a 6-cm scalp laceration over the right temporal area and obvious ecchymoses and abrasions over the chest wall and abdominal wall. The abdomen was tense and distended, and there appeared to be a gravid uterus.

Management Course

Needle decompression of the right-sided tension pneumothorax allowed the patient to regain a pulse (124 beats per minute) and blood pressure (105/75 mmHg). After needle decompression was completed, an ultrasound examination was performed to quickly assess for fetal viability since the patient's presenting vital signs indicated that an emergent perimortem cesarean section be considered. The patient's ultrasound examination revealed a normal uterus without evidence of a fetus; this finding was later confirmed by a negative pregnancy test. The patient's FAST examination was positive for free intraperitoneal fluid, but the patient's condition had stabilized allowing further diagnostic imaging. The patient's abdominal CT scan revealed a cirrhotic liver, a large amount of free fluid consistent with ascites, and no evidence for solid organ or intestinal injury. The patient was noted to have a left mid-shaft femur fracture. The patient was transferred to the surgical intensive care unit for orthopedic and neurosurgical consultation and further management of her injuries.

Commentary

In this case, a severely injured woman, who initially presented pulseless and appeared to be pregnant, would have been a candidate for an emergent perimortem cesarean section if there was a viable fetus of greater than 24 weeks of gestational age. The immediate use of a focused emergency ultrasound examination identified that the patient was, in fact, not pregnant and eliminated the possibility of emergent cesarean section. Free fluid from ascites is a potential pitfall for the FAST examination and is discussed further in Chapter 5 (Trauma).

Case 2

Patient Presentation

A 30-year-old woman, G3P2, 34 weeks pregnant, presented to a small rural emergency department with severe abdominal pain and vaginal bleeding. She expressed that the pain was of sudden onset and did not feel like the contractions of her previous two pregnancies. On physical examination, her blood pressure was 140/90 mmHg, pulse was 115 beats per minute, and respirations 24 per minute. Perineal inspection revealed a moderate amount of frank blood on the sheet with no evidence of crowning.

Management Course

Intravenous access was obtained. The obstetrician was paged to come immediately to the hospital. Since digital cervical examination was contraindicated in this patient, the emergency physician performed an emergency ultrasound examination to assess the status of the fetus. Fetal cardiac activity was confirmed and measured to be 104 beats per minute. The placenta was seen in the posterior fundus and no evidence of placenta previa was visualized. The emergency physician immediately notified labor and delivery personnel to prepare for a crash cesarean section for presumed placental abruption while the patient was rapidly transported to the unit. Rapid evaluation by the obstetrician confirmed the findings, and immediate cesarean section was performed, resulting in the delivery of a live 34-week infant with Apgar scores of 5 and 8 at 1 and 5 minutes, respectively. Examination of the placenta demonstrated evidence of a severe abruption.

Commentary

In this case of a patient with third-trimester vaginal bleeding and abdominal pain, the emergency ultrasound examination revealed evidence of fetal distress and the absence of placenta previa, prompting a presumptive diagnosis of placental abruption. Advance notification to labor and delivery personnel during patient transportation saved crucial minutes from arrival to time of delivery, and likely contributed to the good outcome of the infant and mother. Cardiotocographic monitoring is also indicated and should be initiated as soon as possible when this diagnosis is considered and delivery is not immediate.

Case 3

Patient Presentation

An 18-year-old pregnant woman presented to the emergency department with a severe asthma attack after smoking crack cocaine. The patient also complained of severe abdominal pain. She could provide only a limited history because of her respiratory distress. She had not received prenatal care and was unsure of her last menstrual period. On physical examination, the patient was lethargic and markedly diaphoretic. Her blood pressure was 150/105 mmHg, pulse was 136 beats per minute, respiratory rate 32 breaths per minute, and oxygen saturation 85% on a nonrebreather mask. She had markedly diminished air flow and faint expiratory wheezing on pulmonary examination. Her abdominal examination revealed a gravid uterus, with the fundus palpable in the mid-epigastric area. She had normal active bowel sounds, was diffusely tender throughout her abdomen, and demonstrated no peritoneal signs. Perineal inspection revealed no vaginal bleeding, amniotic fluid, or signs of crowning.

Management Course

Intravenous access was obtained and a continuous albuterol nebulization was administered. Since the patient began to show signs of impending respiratory arrest, she was endotracheally intubated and placed on mechanical ventilation. The emergency physician performed an ultrasound examination to assess the status of the pregnancy and ordered cardiotocographic monitoring. She identified a fetus with a heart rate of 170 beats per minute and a biparietal diameter consistent with a 34-week gestation. No obvious placental abruption was seen and the cervical length was noted to be 3.5 cm without funneling. The emergency physician also did not note any signs of biliary disease. The patient was admitted to the medical intensive care unit for further treatment of her status asthmaticus and for continued cardiotocographic monitoring.

Commentary

After the airway was secured in this young pregnant woman and treatment for her status asthmaticus continued, emergency ultrasound allowed for the assessment of gestational age and fetal well-being. The focused ultrasound examination also was used to screen for potential causes of her abdominal pain, including cholecystitis and preterm labor. Transabdominal ultrasound demonstrated no evidence of cervical dilation; this information was critical for determining whether there was a need for emergent obstetrical intervention. Further evaluation by cardiotocographic monitoring was necessary in this patient to monitor for signs of fetal distress or development of uterine irritability that could have been indicative of fetal hypoxia, placental abruption, or preterm labor due to maternal cocaine abuse or respiratory failure.

We would like to acknowledge Dr. Katie Bakes and Dr. Eric Snoey for their work on the first edition of this chapter.