Chapter 12. First-Trimester Pregnancy

Ultrasonography is the primary imaging modality used in pregnancy.1–4 In first trimester pregnant patients who present with vaginal bleeding or abdominal pain, ultrasound can be used to distinguish ectopic pregnancy from threatened abortion or embryonic demise. The primary goal of emergency sonography of the pelvis in the first trimester is to identify an intrauterine pregnancy, which essentially excludes the diagnosis of ectopic pregnancy.5 Secondary objectives are to detect extrauterine signs of an ectopic pregnancy, estimate the viability of an intrauterine pregnancy, and characterize other causes of pelvic pain and vaginal bleeding. In addition, sonographic detection of free fluid outside of the pelvis can help emergency physicians expedite the care of a patient with a ruptured ectopic pregnancy.6 Emergency bedside sonography is not intended to define the entire spectrum of pelvic pathology in early pregnancy. A follow-up comprehensive pelvic ultrasound examination is indicated after the initial focused bedside examination, the timing of which is dictated by the clinical scenario.

Abdominal or pelvic pain and vaginal bleeding are common complaints during early pregnancy. Challenges to emergency or acute care physicians include making the diagnosis of pregnancy and then using available diagnostic tools to determine the etiology of the patient's complaint.

The development of sensitive pregnancy tests has made a missed diagnosis of early pregnancy unlikely. Modern qualitative urine tests for human chorionic gonadotropin (β-hCG) have a threshold of about 20 IU/L and allow detection of pregnancy as early as 1 week post-conception (3 weeks' gestational age). False-negative urine tests may occur when the urine is highly dilute (specific gravity <1.010), and obtaining a quantitative serum β-hCG should be considered in such cases.7

Once pregnancy is recognized in a symptomatic or high-risk patient, complications of early pregnancy, particularly ectopic pregnancy, must be considered. Those patients with pelvic or abdominal pain, vaginal bleeding, dizziness, syncope, or any risk factors for ectopic pregnancy need to have the status of their pregnancy evaluated. The location, viability, and gestational age of the pregnancy are important factors in establishing a diagnosis. Other findings such as free intraperitoneal fluid in the pelvis or a pelvic mass may also impact the patient's management.

Many diagnostic tests can be used to detect complications of early pregnancy. Serum β-hCG and progesterone levels, suction curettage, culdocentesis, and laparoscopy yield some information, but none can identify the entire spectrum of pathology like pelvic sonography. Furthermore, other imaging modalities, like CT and MRI, are not commonly used for detecting complications of early pregnancy.

The hormone β-hCG is produced by the trophoblasts during early pregnancy. Serum β-hCG levels rise exponentially in early pregnancy and can be used as a marker to date normal pregnancies. However, abnormal pregnancies have widely varying β-hCG levels, so a single level cannot differentiate a normal intrauterine pregnancy from an ectopic pregnancy or other abnormality.8

Progesterone is produced by the corpus luteum in early pregnancy and serum levels remain relatively high during a normal pregnancy. Serum levels are generally lower in abnormal pregnancies, including ectopic pregnancy, and fall with pregnancy failure. Clinicians who do not have bedside ultrasound immediately available have utilized progesterone levels to help differentiate between a normal pregnancy and a possible ectopic with some success.9, 10 These methods, however, have not proven to be as efficient or as accurate as protocols that incorporate initial transvaginal sonography. Preliminary reports suggest that progesterone may have a role in further categorizing patients who have an initial indeterminate transvaginal ultrasound. One study found that patients with a progesterone level ≥ 11 ng/mL are significantly more likely to have an early intrauterine pregnancy rather than an ectopic or an abortion (sensitivity 91%, specificity 84%).11 Another study demonstrated a progesterone level less than 5 ng/mL to be 88% sensitive (although only 40% specific) in detecting ectopic pregnancy in the setting of an indeterminate (nonspecific free fluid or empty uterus) ultrasound.12

Suction curettage of the uterus can provide a definitive diagnosis of an intrauterine pregnancy if chorionic villi are identified. However, this test terminates an intrauterine pregnancy, making it applicable only when termination is desired or the pregnancy has obviously failed. Because it is invasive and other tests can provide similar information, suction curettage is rarely useful in the initial emergency evaluation during early pregnancy.

Culdocentesis is needle aspiration of the pelvic cul-de-sac through the posterior fornix of the vagina. Aspiration of blood is considered indicative of an ectopic pregnancy although blood in the cul-de-sac can be seen with an intrauterine pregnancy. However, culdocentesis is not very sensitive, especially for detecting nonruptured ectopic pregnancies.5, 13–15 It now has a very limited role and is recommended only when ultrasound is not available.16

Laparoscopy is an excellent test for visualizing extrauterine pelvic pathology, especially ectopic pregnancy.17 However, it does not give any information about intrauterine contents or fetal viability. Recently laparoscopy has been utilized less frequently because sonography is noninvasive and can provide more information.14 Laparoscopy can be used as a therapeutic tool and a diagnostic adjunct when sonography is nondiagnostic.

There are many advantages to using sonography in the first trimester of pregnancy. It is an ideal diagnostic tool in this setting since it can visualize both intrauterine contents and the extrauterine pelvic pathology. When used judiciously, ultrasound has no known adverse effects on the embryo and can be repeated as needed. Unlike curettage or culdocentesis, ultrasound is noninvasive and well tolerated by most patients.18 Unlike curettage or laparoscopy, ultrasound can directly visualize the intrauterine or extrauterine location of a pregnancy.19 Unlike serum markers, ultrasound can immediately identify an abnormal pregnancy or evaluate fetal viability. Also, ultrasound can accurately measure the gestational age of a pregnancy, whereas serum markers can only give a gross estimation. Finally, patients with an ectopic pregnancy can be risk-stratified using ultrasound by estimating the size of an extrauterine mass or the amount of free intraperitoneal blood.

A disadvantage of using ultrasound in early pregnancy is that a pregnancy may not be visible between 3 and 5 weeks' gestational age. During this time, sensitive urine pregnancy tests are positive but the gestation is usually too small to identify, even with transvaginal ultrasound. Another disadvantage of using ultrasound is that it is equipment and operator dependent. Clinicians who make important patient management decisions based on ultrasound results must know the limitations of each study based on who is performing the examination and what type of equipment is being used.

Any patient who is at risk for complications of early pregnancy is a candidate for pelvic sonography. Symptoms and physical examination findings include pelvic or abdominal pain or tenderness, vaginal bleeding, dizziness, syncope, a pelvic mass, or uterine size that does not correlate with the gestational age. Risk factors for ectopic pregnancy include pelvic inflammatory disease, tubal ligation, tubal surgery, increased maternal age, intrauterine contraceptive devices, prior ectopic pregnancy, and a history of infertility.20 Most patients with an ectopic pregnancy present with abdominal or pelvic pain, vaginal bleeding, or dizziness, but some are relatively asymptomatic. Since no specific sign or symptom is absolute, physicians must have a high index of suspicion so that subtle presentations are not overlooked. Also, any woman of childbearing age who presents with shock of unknown etiology should have an immediate abdominal and pelvic ultrasound examination, even before a pregnancy test is completed.6

The main indication for emergency pelvic sonography in the first trimester is to differentiate an intrauterine pregnancy from an ectopic pregnancy. Sonography can immediately establish one of these diagnoses in most patients with first trimester complaints.19

• Intrauterine pregnancy
• Ectopic pregnancy

Emergency pelvic sonography is also useful for the diagnosis of the following conditions in the first trimester of pregnancy:

• Pregnancy loss
• Multiple pregnancy
• Pelvic mass
• Ovarian torsion
• Gestational trophoblastic disease

A normal intrauterine pregnancy is the most common sonographic finding during the first trimester. Even novice sonologists can use pelvic ultrasound effectively because identifying an intrauterine pregnancy is straightforward and this finding virtually eliminates the possibility of an ectopic pregnancy.21 About 70% of patients who present with abdominal pain or vaginal bleeding in the first trimester will have an intrauterine pregnancy visualized with bedside ultrasound and will not require further testing.22 Care must be taken when using sonography between 3 and 5 weeks' gestational age because it is easy to confuse sonographic signs of an early intrauterine pregnancy with those of an ectopic pregnancy.

Identifying an intrauterine pregnancy with cardiac activity can give patients some reassurance about the outcome of their pregnancy. Those patients with a finding of embryonic cardiac activity have a much lower incidence of pregnancy loss than other patients with similar symptoms.23, 24 However, physicians should be careful not to give patients false hope about their pregnancy. Even when a normal intrauterine pregnancy is discovered, it is prudent to inform patients that emergency bedside sonography is a focused examination only and will not detect fetal anomalies. Also, patients with abdominal pain or vaginal bleeding still have a significant chance of pregnancy loss.

Dating an intrauterine pregnancy is not as important as excluding an ectopic pregnancy. However, when the uterine size does not correlate with the gestational age or when the last menstrual period is unknown, sonography is indicated to date the pregnancy. This is very common because about half of all pregnant women cannot remember their last menstrual period. Pregnancy dating is simple and rapid with modern ultrasound equipment. Sonographic dating during the first trimester is more accurate than dating later in pregnancy. A few minutes spent measuring an embryo will be much appreciated by the patient's obstetrician, especially in patients who have unclear menstrual dates or are noncompliant with prenatal care. This early measurement becomes more important near term when the obstetrician is considering induction of labor in a patient whose uterine size does not correlate with gestational age.

Ectopic pregnancy occurs in about 2% of all pregnancies in the United States.13, 14, 25 However, symptomatic patients who present to an emergency setting have a much higher incidence, as high as 4.5–13% in some reports.9, 26–28 The incidence of ectopic pregnancy has quadrupled in the last 20 years.13 During the same period of time, the case-fatality rate for ruptured ectopic pregnancies has decreased significantly. This decrease is due to earlier diagnosis and treatment secondary to increased awareness and improved diagnostic capabilities, such as transvaginal sonography.14 Despite these improvements, a significant percentage of ectopic pregnancies is still missed.29 Also, ectopic pregnancy remains the leading cause of maternal death during the first trimester of pregnancy.30

Heterotopic pregnancy, which is a concomitant intrauterine and extrauterine pregnancy, has also become more common in the last few decades. In 1948, the incidence of heterotopic pregnancy was estimated to be 1 per 30,000 pregnancies, based on a theoretical calculation and assuming an ectopic pregnancy rate of 0.37%.31 Now that the ectopic pregnancy rate is about 2%, it is reasonable to expect that the rate of heterotopic pregnancy is higher than previously estimated. There is some suggestion that the incidence of heterotopic pregnancy may be as high as 1 in 8,000 pregnancies, but this may be practice specific.31–36 The incidence is much higher in patients taking ovulation-inducing medications or undergoing in vitro fertilization (as high as 1 per 100 pregnancies).37, 38

Emergency or acute care physicians have an important role in preventing morbidity and mortality from ectopic pregnancy.39 Early diagnosis of ectopic pregnancy allows conservative treatment options, like methotrexate therapy.14, 40 Pelvic ultrasound is the main diagnostic modality that allows an early diagnosis to be made.

When emergency physicians perform bedside transvaginal sonography, pregnant patients have a shorter length of stay in the emergency department.41–43 Also, bedside pelvic ultrasound screening by clinicians is more cost-effective than ordering comprehensive pelvic sonography on every patient with a possible ectopic pregnancy.44 Most importantly, a protocol, which includes bedside transvaginal ultrasound by emergency physicians, has been shown to decrease the incidence of discharged patients returning with a subsequent ruptured ectopic pregnancy.22, 26, 45

Algorithm with Transvaginal Sonography and β-HCG Discriminatory Zone

Prior to the development of ectopic pregnancy algorithms and the widespread use of transvaginal sonography, the diagnosis of about half of all ectopic pregnancies was missed, and about half of those ruptured prior to their next presentation.26, 46, 47 In the 1980s, ectopic pregnancy was one of the leading causes of emergency physician malpractice suits.48, 49 Algorithms that incorporate transvaginal sonography and a β-hCG discriminatory zone have improved diagnostic accuracy and reduced the incidence of patients who are discharged and subsequently present with a ruptured ectopic pregnancy.19, 26

One algorithm utilizes emergency bedside transvaginal sonography as the initial diagnostic step for all patients at risk for ectopic pregnancy, before a quantitative serum β-hCG is obtained (Figure 12-1).4, 26, 45, 47,50–59 Transvaginal sonography can establish a diagnosis of intrauterine pregnancy or ectopic pregnancy in 75% of patients at the time of their initial presentation.19 If emergency bedside sonography demonstrates an intrauterine pregnancy or an ectopic pregnancy, then the work-up is complete. When no intrauterine pregnancy or ectopic pregnancy is identified, then the bedside ultrasound examination is indeterminate, and at this point a quantitative serum β-hCG level and a comprehensive pelvic ultrasound examination should be ordered. Again, if the comprehensive study shows an intrauterine pregnancy or an ectopic pregnancy, then the work-up is complete. If either the bedside or comprehensive ultrasound examination demonstrates nonspecific signs of an ectopic pregnancy, then the risk is very high. Therefore, this situation should be managed in the same manner as a clear ectopic pregnancy, and an obstetrics consult should be obtained. If both sonograms show no intrauterine pregnancy and no signs of an ectopic pregnancy, then the management depends on the serum β-hCG level. Patients with an indeterminate ultrasound examination and a β-hCG level above the discriminatory zone (β-hCG >1,000 mIU/mL) have a presumed ectopic pregnancy or embryonic demise and require an immediate obstetrics consultation. Those with an indeterminate ultrasound examination and a β-hCG level below the discriminatory zone (β-hCG < 1,000 mIU/mL) may have a small ectopic pregnancy, a very early intrauterine pregnancy, or embryonic demise. If hemodynamically stable and with an unremarkable physical examination, these patients can be discharged home without an obstetrics consult but they should be given clear ectopic pregnancy discharge instructions and scheduled for close follow-up in 2–3 days for a repeat ultrasound examination and serum β-hCG level.60

Similar algorithms, incorporating emergency bedside transvaginal sonography, have been shown to improve the quality of patient care and to be more cost-effective than other approaches.19, 26, 44, 45

Quantitative Serum β-HCG and Discriminatory Zone

Serum β-hCG rises exponentially and predictably during the first 6–8 weeks of pregnancy and peaks at about 100,000 mIU/mL in a normal pregnancy. Serial β-hCG levels are useful for differentiating normal pregnancies from abnormal pregnancies. The serum level should increase by at least 66%, multiplying by 1.6, every 48 hours, and may even double between 36 and 48 hours. An abnormally slow rise in β-hCG indicates an abnormal pregnancy, either an ectopic pregnancy or embryonic demise. A normal or expected rise in β-hCG, however, does not necessarily exclude an ectopic.

Quantitative β-hCG measurements are currently standardized in relation to the International Reference Preparation (IRP). The reference standard for all β-hCG levels discussed in this chapter is the IRP. The standard method for reporting IRP β-hCG levels is in mIU/mL. Other reference standards are referred to in the literature, and it is important to distinguish between them since they are not equivalent. The Second International Standard is roughly equal to one half of the IRP and the Third International Standard is roughly equal to the IRP. In this chapter, β-hCG concentrations are reported in relation to the IRP, in mIU/mL.

A single serum β-hCG level is not as useful as serial levels because it does not differentiate a normal early intrauterine pregnancy from an ectopic pregnancy.61 A common misconception is that a very low β-hCG level rules out ectopic pregnancy. Recent studies show that about 40% of ectopic pregnancies present with a β-hCG level less than 1,000 mIU/mL and about 20% present with a β-hCG level less than 500 mIU/mL.19, 62 In fact, patients who present with a β-hCG level less than 1,000 mIU/mL have a higher risk of ectopic pregnancy than other patients.19, 63, 64 Furthermore, a low β-hCG level does not predict a benign course. Approximately 30–40% of ectopic pregnancies with a β-hCG level less than 1,000 mIU/mL will be ruptured at the time of diagnosis.19, 62, 63

The “discriminatory zone” is a concept that was developed to allow the complementary use of pelvic ultrasound and a single serum β-hCG level to help determine the likelihood of ectopic pregnancy. The discriminatory zone is the β-hCG level above which an intrauterine pregnancy should be consistently visualized by pelvic sonography. Patients with a β-hCG level above the discriminatory zone who do not have an intrauterine pregnancy on ultrasound examination are presumed to have an ectopic pregnancy until proven otherwise. This is the concept that led to the use of the discriminatory zone in previous ectopic pregnancy algorithms. Older algorithms used the β-hCG discriminatory zone to limit the use of pelvic sonography since it was thought that only patients with levels greater than 1,000 mIU/mL would benefit from an ultrasound examination.47, 52 When outdated algorithms are applied, however, a significant percentage of ectopic pregnancies will be missed.47

Recent studies clearly show the benefit of performing pelvic sonography on all patients with a possible ectopic pregnancy, regardless of their β-hCG level.19, 26, 57, 62, 63, 65 Although a normal pregnancy will not be visualized when the β-hCG level is low, many ectopic pregnancies are easily identified when the β-hCG level is less than 1,000 mIU/mL. In fact, transvaginal sonography can detect about half of ectopic pregnancies with β-hCG levels less than 1,000 mIU/mL.19, 60, 62, 63, 66–68

In this chapter's algorithm, the discriminatory zone serum β-hCG level is used to help guide the management of patients with indeterminate pelvic ultrasound examinations. The discriminatory zone β-hCG level of 1,000 mIU/mL was chosen because this is the level above which an intrauterine pregnancy can be consistently visualized by comprehensive transvaginal sonography.30, 53, 62, 69 Individual hospitals and clinics should choose their own discriminatory zone in collaboration with their obstetrics consultants and those who will perform their comprehensive ultrasound studies.

Indeterminate Ultrasound Examinations

An “indeterminate” ultrasound examination in early pregnancy demonstrates no signs of intrauterine pregnancy or an ectopic pregnancy. One study attempted to subclassify patients with an indeterminate ultrasound examination based on their intrauterine findings.70 Patients with a completely empty uterus and normal thin midline stripe had a 27% chance of an ectopic pregnancy and a 10% chance of an intrauterine pregnancy. Those with a nonspecific endometrial fluid collection had a 13% chance of an ectopic pregnancy and a 25% chance of an intrauterine pregnancy. Patients with intrauterine echogenic material had a 5% chance of ectopic pregnancy and none had an intrauterine pregnancy.

Approximately 15% of patients who are evaluated for a possible ectopic pregnancy have a β-hCG level greater than 1,000 mIU/mL and an indeterminate ultrasound.19, 70 Roughly 20% of these patients have an ectopic pregnancy.58, 59, 70, 71

Management and Disposition

Patients diagnosed with an ectopic pregnancy have traditionally required surgery, which is usually a laparoscopic procedure. Although less successful compared to surgery,72, 73 medical therapy has become increasingly popular, with single-dose intramuscular methotrexate therapy being the most common regimen.74 This regimen has a success rate ranging from 64 to 94%.14, 75–77 Clinical and sonographic criteria can help obstetricians decide which patients are candidates for medical therapy instead of surgery. Higher serum β-hCG levels, especially above 10,000 mIU/mL, the presence of a yolk sac, and endometrial stripe thickness greater than 12 millimeters are associated with failure of methotrexate therapy.40, 75, 77–81 Also, an adnexal mass greater than 4 cm in diameter, the presence of embryonic cardiac activity, a large amount of pelvic free fluid, and severe pain should be considered relative contraindications to medical management.14, 82 Clinical signs of shock along with free intraperitoneal fluid outside of the pelvis, such as in the hepatorenal space, are indications for surgery and contraindications to medical therapy.6, 14, 30

Patients with an unclear diagnosis of ectopic pregnancy need serial sonography and serial β-hCG levels. Obstetricians may be unwilling to initiate therapy in such patients for fear of interrupting an intrauterine pregnancy. Patients who have a β-hCG level greater than 1,000 mIU/mL and unclear or questionable sonographic findings should ideally be observed in the hospital. Repeat sonography and β-hCG level at 12–24 hours will make the diagnosis more clear. Those with no mass, free fluid, or other signs of ectopic pregnancy and a β-hCG level less than 1000 mIU/mL are safe to be discharged with early follow-up for repeat sonography and β-hCG level in 24–48 hours.13, 42, 45, 52

The majority, up to 70% of all ectopic pregnancies, will spontaneously resolve without any treatment.83, 84 Therefore, expectant management may be reasonable in selected cases. Candidates for expectant management must have minimal symptoms, a small ectopic mass, and a low β-hCG level. Excellent clinical, sonographic, and laboratory follow-up must be ensured if expectant management is attempted.

Diagnosing pregnancy loss is not as urgent as excluding an ectopic pregnancy. It is important, however, for emergency or acute care physicians to be aware of the sonographic features of pregnancy loss. It is helpful to know the risks of pregnancy loss related to specific ultrasound findings. This information will allow physicians to do a better job of counseling patients and making reasonable management plans for those with a threatened abortion.

Vaginal bleeding is a very common presentation and occurs in about 25% of all clinically apparent early pregnancies.69, 85, 86 About 40–50% of these patients will eventually be diagnosed with pregnancy loss.19, 30, 87–89 A threatened abortion is a significant source of anxiety for pregnant patients. Concern for the viability of the pregnancy is usually the primary reason for presentation. Pelvic sonography is very useful in patients with a threatened abortion because it provides an immediate diagnosis in about half of all patients with subsequent pregnancy loss.87 Those without a definitive diagnosis require serial pelvic sonography and β-hCG levels.

Spontaneous abortion refers to expulsion of a nonviable pregnancy from the uterus before 20 weeks' gestational age. Microscopic identification of chorionic villi or obvious products of conception are required to make a definitive diagnosis. A completed spontaneous abortion can be diagnosed when all products of conception have been expelled. This usually occurs shortly after embryonic demise but may be delayed for days to weeks. Sonographically, an empty uterus should be seen after a completed spontaneous abortion. This finding indicates that the patient can be managed expectantly without curettage.90–92

Incomplete abortion is a nonspecific term used when a pregnancy has failed but all of the products of conception have not been expelled from the uterus. The terms embryonic demise, blighted ovum, and retained products of conception are all synonymous with incomplete abortion. Patients with an incomplete abortion may experience continued bleeding, infection, and anxiety, so it is important to make the diagnosis as soon as possible after embryonic demise has occurred. Patients with an incomplete abortion may require suction and curettage to remove retained products of conception.92, 93 Sonography is the only diagnostic modality that can directly assess intrauterine contents before a curettage is performed.

The term inevitable abortion implies that expulsion of uterine contents is in progress. Patients with an inevitable abortion have an open cervical os on physical examination. Pelvic sonography may show a separated gestational sac lying low within the uterus.69 It is reasonable for physicians to use bedside pelvic sonography to help make initial management decisions in patients with a threatened abortion. However, it is prudent to confirm the diagnosis of embryonic demise with a comprehensive pelvic ultrasound prior to evacuation of intrauterine products. Also, it is important not to give patients false reassurance. Even when a completely normal intrauterine pregnancy is seen, they should be aware that there is still a chance of subsequent pregnancy loss.

Sonographic signs of a normal intrauterine pregnancy are reassuring and decrease the likelihood that a pregnancy will be lost.23, 87, 94–96 In asymptomatic patients, those without threatened abortion, the rate of first trimester pregnancy loss decreases as the gestational age increases and as more normal structures can be identified with sonography. The rate of loss after only a gestational sac is identified is 11.5%. The rate decreases to 8.5% after a yolk sac is identified and to 7.2% after an embryo (2–5 mm) is identified. When a larger embryo is seen, the loss rate is even lower: 3.3% with a 6- to 10-mm embryo and 0.5% with an embryo greater than 10 mm. In addition, there is a 2% risk of pregnancy loss after the first trimester in pregnancies that previously appeared viable by ultrasound.95

As stated above, patients presenting with a first trimester threatened abortion have a 40–50% chance of pregnancy loss.19, 30, 87–89 If embryonic cardiac activity can be seen, however, the rate of subsequent pregnancy loss is lower at 15–20%.23, 87 Also, as the gestational age and the size of the embryo increase, cardiac activity is more reassuring. Very early in the first trimester, when the embryo is less than 5 mm long, patients with a threatened abortion and cardiac activity have a loss rate of about 24%.96 Those with a threatened abortion and cardiac activity near the end of the first trimester have a very low rate of pregnancy loss.24

Characterizing a multiple pregnancy (twins, triplets, etc.) is typically not in the realm of emergency medicine. However, timely pelvic sonography is indicated when menstrual dates do not correlate with the size of the patient's uterus. In such cases, sonographic pregnancy dating and evaluation for multiple pregnancy or molar pregnancy should be performed. Also, multiple pregnancies are often an incidental finding when sonography is performed for other indications, such as ruling out an ectopic pregnancy. Regardless of the indication for the sonogram, finding a multiple pregnancy is significant since the pregnancy will then be categorized as high risk and the patient will need close follow-up with an obstetrician.

Twin pregnancies are more likely to have fetal anomalies, premature delivery, and low birth weight. Early sonographic evaluation of a multiple pregnancy is important because differentiating dichorionic from monochorionic twins is much easier during the first trimester. Fraternal (dizygotic) twins are always dichorionic and diamnionic but identical (monozygotic) twins may be dichorionic, monochorionic, diamnionic, or monoamnionic, depending on when the zygote splits. Determining chorionicity is important since monochorionic twins have a mortality rate two to three times higher than dichorionic twins. Monochorionic twins share a single placenta, so they are at risk of twin transfusion syndrome, twin embolization syndrome, and acardiac parabiotic twin syndrome. In addition, determining amnionicity is important since monoamniotic twins are at risk for cord knots, wrapping of the cord around a cotwin, or locking of twins during delivery.

When imaging a multiple pregnancy, physicians should try to record quality images that clearly show the chorionicity and amnionicity. If chorionicity and amnionicity cannot be determined, then the patient should have a comprehensive ultrasound examination within several days. Also, it is important to inform patients that about 25% of twin pregnancies diagnosed during the first trimester will become singleton pregnancies by the second trimester.97, 98

A pelvic mass may be noted in the first trimester of pregnancy during the physical examination or routine pelvic ultrasound examination. Physicians who perform bedside sonography need to have some basic knowledge of pelvic masses so they can make reasonable management plans. Most pelvic masses found in the first trimester are benign and require no treatment. They all, however, require close follow-up with serial sonography because some masses are at risk of hemorrhage, torsion, rupture, dystocia, and malignancy. Surgery will be required in about 1 per 1,300 pregnancies to exclude malignancy or to deal with one of the above complications. About 3% of all masses discovered during pregnancy have malignant potential.99

In general, patients with masses less than 5 cm in diameter in early pregnancy are treated conservatively and followed with serial sonography. Those presenting with peritoneal signs or severe pain may need immediate surgery because of rupture or torsion of a mass. Masses that are large, cause pain, or grow rapidly may require surgery. Those containing large solid areas, solid irregular areas, papillary excrescences, and irregular septae are at higher risk of malignancy. Also, the presence of ascites, in addition to a cystic pelvic mass, increases the chance of malignancy.100 If surgery is required, then the optimal period is during the second trimester, when maternal and fetal risks are smallest.

The most common mass seen in early pregnancy is a corpus luteum cyst. The corpus luteum secretes progesterone to support the early pregnancy. A corpus luteum cyst is usually less than 5 cm in diameter and appears as a thin-walled unilocular structure surrounded by normal ovarian parenchyma. The appearance may vary substantially and the size may be greater than 10 cm. Hemorrhage into a corpus luteum cyst can cause the appearance of internal echogenic debris and septae.30 Corpus luteum cysts usually regress spontaneously prior to 18 weeks of gestation.

A theca lutein cyst is an exaggerated corpus luteum and occurs in patients with very high β-hCG levels. Theca lutein cysts are commonly seen in patients with gestational trophoblastic disease and ovarian hyperstimulation from fertility medications. They appear as large multiseptated cystic masses. Theca lutein cysts usually resolve spontaneously once the abnormal stimulus is removed.

Uterine leiomyomas, or fibroids, are solid pelvic masses that are very common and may enlarge during pregnancy because of increased estrogen levels. They usually appear as relatively hypoechoic masses within the uterine wall and are sometimes confused with a simple muscular contraction of part of the uterine wall. Fibroids can have many different appearances, depending on the amount of smooth muscle and hyaline they contain and whether they have undergone hemorrhagic degeneration. They may contain calcifications or cystic areas of degeneration. Small fibroids tend to enlarge during the first and second trimesters but larger fibroids tend to enlarge only during the first trimester.101 All fibroids tend to decrease in size during late pregnancy. Patients with multiple fibroids have a higher risk of bleeding, premature contractions, malpresentation, and retained products.100 Large fibroids located in the lower part of the uterus during late pregnancy can obstruct labor and necessitate a cesarean section.

The most common complex mass seen in early pregnancy is a teratoma, or dermoid cyst.99, 100 These tumors arise from germ cells within the ovary and contain heterologous tissue like fat, skin, hair, and teeth. Sebaceous material within a dermoid can appear as a fluid–fluid level and teeth are very echogenic with distal shadowing. Dermoids are prone to torsion and rupture. Leaking of dermoid fluid can cause granulomatous peritonitis and sudden rupture can cause an acute abdomen.100

Mucinous and serous cystadenomas are ovarian epithelial neoplasms; they are the most common cystic tumors that enlarge during pregnancy.102 Both of these tumors can appear as multicystic masses. Mucinous cystadenomas usually contain multiple thick internal septations and serous cystadenomas usually appear as unilocular structures. Again, pelvic masses that have internal septations and papillary excrescences are more likely to be malignant.100

Emergency sonologists typically do not attempt to characterize pelvic masses using sonography. However, these physicians will inevitably discover pelvic masses as incidental findings. When this occurs, most patients will need a comprehensive ultrasound examination and close follow-up with an obstetrician. Patients should be informed when a mass is found, and they should understand that bedside sonography is a screening tool and that further work-up is needed.

Adnexal torsion is uncommon but about 20% of all cases occur during pregnancy.103, 104 Also, most cases occur during the first trimester.99, 105 Pregnant patients may be predisposed to torsion because of increased ovarian arterial flow and decreased ovarian venous flow, causing ovarian edema and enlargement. Torsion almost always occurs in the setting of an enlarged ovary or an ovarian mass; torsion rarely occurs in a normal size ovary. Recently, ovarian hyperstimulation from fertility medications has been recognized as a risk factor for adnexal torsion because of ovarian enlargement.

Pain is the most common symptom of adnexal torsion. The diagnosis of torsion may be easily missed during pregnancy because pain may be attributed to the gravid uterus, the round ligament, or an adnexal mass. Further delay may occur because of the poor accuracy of Doppler ultrasound, which may miss up to 60% of cases of adnexal torsion.106 Also, when a cystic ovarian mass is present, blood flow to the ovary may be difficult to visualize using pulse wave Doppler, even though torsion has not occurred.

Simple gray-scale pelvic sonography may be of some help in diagnosing adnexal torsion.107, 108 Finding a unilaterally enlarged ovary with multifollicular enlargement or any adnexal mass makes torsion more likely. Most patients with torsion have free fluid in the pelvic cul-de-sac, probably as a result of obstruction of venous and lymphatic drainage.107, 109 Finding normal-size ovaries and no pelvic free fluid makes the diagnosis of adnexal torsion highly unlikely.

Most diagnoses of adnexal torsion are delayed because of atypical clinical presentations and poor sensitivity of diagnostic modalities.110 This may be especially detrimental in pregnancy causing maternal morbidity and fetal mortality. Therefore, it is prudent to have a high index of suspicion when there is no clear etiology for abdominal, pelvic, flank, or groin pain. Also, when the diagnosis is strongly suspected, negative diagnostic studies should not deter consultation and further evaluation.111 Laparoscopy has been used during pregnancy as both a diagnostic and therapeutic modality.

Gestational trophoblastic disease (GTD) is a proliferative disease of the trophoblast. It occurs in about 1 per 1,700 pregnancies in the United States but is much more common in some other parts of the world.112 GTD may occur with an intrauterine pregnancy or an ectopic pregnancy, or after a spontaneous abortion or full-term pregnancy. Most cases of GTD (80%) present as a benign hydatidiform mole. More malignant forms of GTD, invasive mole (12–15%), and choriocarcinoma (5–8%) may develop after a hydatidiform mole. Hydatidiform moles usually involve the entire placenta but a mole involving only part of the placenta can be associated with a live pregnancy.

Early in pregnancy, GTD may present with vaginal bleeding, uterine size that is too large for dates, persistent severe hyperemesis gravidarum, or early preeclampsia. Sometimes, the first clue to the diagnosis is a markedly elevated serum β-hCG level, usually greater than 100,000 mIU/mL. It has been shown that qualitative β-hCG urine assays may be falsely negative in the setting of GTD with markedly elevated serum β-hCG.113 GTD is often discovered during routine pelvic sonography for pregnancy dating or other indications.

Ultrasound is the preferred modality for diagnosing GTD and both transabdominal and transvaginal sonography are usually diagnostic.114 The classic finding, described as having a grape-like appearance, is an intrauterine echogenic mass containing diffuse small hypoechoic vesicles. In the first trimester, GTD may not be as obvious and can be confused with an incomplete abortion. In about half of cases of GTD, a theca lutein cyst is seen in the adnexa.

Early diagnosis and prompt treatment are the key to a favorable outcome. A hydatidiform mole usually resolves completely with evacuation of the uterus. Choriocarcinoma can metastasize to the lung, liver, and brain. It is very sensitive to chemotherapy but morbidity and mortality depend on the extent of metastases and early aggressive treatment.

The uterus is located in the center of the true pelvis between the bladder anteriorly and the rectosigmoid colon posteriorly. The uterus is a thick-walled muscular structure that is about 6–7 cm long and about 3–4 cm in transverse and anterior–posterior diameters. It is shaped like an inverted pear and the uterine body is the widest portion. The cervix is the narrowest portion and is anchored to the posterior bladder by the parametrium. The cervix meets the vagina at the level of the bladder angle and protrudes into the anterior wall of the vagina. When the uterus is in the normal anteflexed position, the longitudinal axes of the uterus and vagina create an angle of about 90 degree. The fallopian tubes enter the body of the uterus laterally, in an area called the cornua. The fundus is the most superior portion of the uterine body above the cornua.

The uterine body and fundus lie inside the peritoneal cavity so intraperitoneal potential spaces exist both anterior and posterior to the uterus. The anterior cul-de-sac, between the bladder and uterus, is usually empty but can contain loops of bowel or free fluid. The posterior cul-de-sac, between the uterus and the rectosigmoid colon, is also known as the “pouch of Douglas” and it usually contains bowel loops. The posterior cul-de-sac is the most dependent intraperitoneal region when the patient is supine; therefore, it is the most common site for pooling of free pelvic fluid.

Lateral to the uterus, the peritoneal reflection forms the two layers of the broad ligament. The broad ligament extends from the uterus to the lateral pelvic sidewalls. The fallopian tubes extend laterally from the body of the uterus in the upper free margin of the broad ligament. The ovaries are attached to the posterior surface of the broad ligament. They are also attached to the body of the uterus by the ovarian ligaments and to the lateral pelvic sidewalls by the suspensory ligaments of the ovary. Normal ovaries are about 2 cm wide and 3 cm long. The ovaries are usually located in a depression on the lateral pelvic walls called the ovarian fossa. However, since the ligaments are not rigid structures, the ovaries may be seen in a number of other locations, especially in women who have previously been pregnant.

While working with a stable patient in need of early first trimester pregnancy evaluation in the emergency department, ultrasonography of the pelvis is most efficiently accomplished immediately following the pelvic examination. This allows for uninterrupted presence of a chaperone that may have assisted with the pelvic examination. Sonographic findings of very early pregnancy and nonpregnant patients can be difficult to distinguish. Therefore, it is often advisable to wait to perform the pelvic examination and subsequent ultrasound evaluation after pregnancy status has been confirmed, usually by urine qualitative β-hCG. Occasionally patients will communicate that they are pregnant when in reality they are not. Waiting for laboratory confirmation of pregnancy status helps avoid the misuse of time and resources looking for a pregnancy that does not exist. On the other hand, if the patient's last menstrual period suggests a sufficiently advanced gestational age, immediate transabdominal ultrasonography can confirm pregnancy and eliminate the need for urine or serum β-hCG.

During transabdominal pelvic ultrasound, the bladder should be full. A longitudinal image of the uterine midline should initially be obtained to determine the location of the body of the uterus, the cervix, and the pouch of Douglas. Significant axial pressure should be applied to produce the best images if this can be tolerated by the patient. After imaging the long axis of the uterus, the probe should be rotated transversely 90 degrees in its long axis to find the ovaries and scan the adnexa. The ovaries are located lateral to the widest portion of the uterus in the transverse plane next to the internal iliac artery and vein. The broad ligament should be followed laterally from the cornual region of the uterus to the ovary on each side.

During transvaginal ultrasonography, the bladder should be empty. The uterus and cervix should serve as anatomic landmarks and initially be visualized longitudinally. Because of anatomic variability, the midline of the uterus may not be in the same plane and consistent with the midline of the patient's body. Ovaries are most easily visualized in the transverse plane after following the broad ligament laterally from the cornual region of the uterus. Evaluation of specific structures such as the uterus, ovaries, or adnexal masses may be enhanced by placement of the probe tip directly over the area of interest. Just as the examiner's hand is used to palpate structures during a routine physical examination, gentle application of axial force on the probe may elicit tenderness and provide important diagnostic information.

Transabdominal and transvaginal sonography are complementary imaging techniques and should be used together. In general, transvaginal imaging should not be performed without also performing a transabdominal scan, but this may not be practical in a busy clinical setting. Transvaginal imaging allows the probe tip to be placed very close to the organ of interest so that high-frequency probes can be used to generate high-resolution images. However, transvaginal probes have a limited field of view and objects more than a few centimeters away from the probe tip may not be seen. Transabdominal sonography uses lower frequency probes so the field of view is much larger and a better overview of pelvic structures can be obtained. The main drawback of transabdominal scanning is that the resolution is lower, so details of small pelvic structures are not as discernible, particularly ovaries and early pregnancies.

Normal Nonpregnant Pelvis

Transabdominal Scanning

Transabdominal scanning is usually accomplished using a 3.5–5 MHz ultrasound probe. The bladder is used as a window in transabdominal scanning, so it should be full to obtain optimal images. In the emergency setting, transabdominal scanning may be performed without a full bladder because it is not practical to have patients drink fluid and wait for an hour while their bladders fill. Intravenous fluid administration will typically lead to rapid bladder filling. Quality images are usually obtained without bladder filling in thin women and those with an anteflexed uterus. Gentle pressure on the probe can also be used to produce good-quality transabdominal images without filling the bladder.

The best transabdominal view for evaluating the uterus and its contents is the standard midline sagittal view (Figure 12-2). To obtain this view, the probe is placed on the abdominal wall in the midline just above the pubic bone, with the probe indicator pointing cephalad (Figure 12-3). By convention, the indicator on the probe should correlate with the left side of the monitor so that in sagittal images cephalad structures are on the left side. This view provides a longitudinal image of the uterus and the entire midline stripe should be visible. The cervix is seen just posterior to the bladder angle with the body of the uterus to the left of the angle and the vaginal stripe to the right. The ovaries can be seen by sliding the probe laterally, with the probe indicator still pointing cephalad, and aiming the beam toward the contralateral adnexa, using the bladder as a window. Sometimes when the bladder is very full or a large pelvic mass is present, better images can be obtained by placing the probe directly over the adnexa.

In some cases it may be easier to visualize the ovaries and other adnexal structures with the standard transabdominal transverse view (Figure 12-4). This view is obtained by placing the probe in the midline of the abdominal wall just above the pubic bone, with the probe indicator pointing to the patient's right side. This view provides a transverse image of the uterus and allows the midline of the uterus and the adjacent adnexa to be seen in the same image if the anatomy cooperates. In transverse images, anatomic structures have the same orientation as on a CT scan: right-sided structures are on the left side of the monitor and left-sided structures are on the right. To examine the entire pelvis in transverse planes, the probe should be kept in the midline suprapubic region with the probe indicator pointed to the patient's right and the beam should be aimed caudad and cephalad (Figure 12-5). This motion will allow the uterus to be viewed in transverse sections from the cervix to the fundus respectively.

The ovaries are most commonly found between the body of the uterus and the pelvic sidewall. In their normal location, the ovaries are bound posteriorly by the internal iliac artery and superiorly by the external iliac vein. These structures can be identified and used to help locate the ovaries. Normal ovaries appear as small discrete hypoechoic structures. Individual ovarian follicles are usually not visible with transabdominal imaging. Normal ovaries are not always seen with transabdominal sonography because they are relatively small and may be camouflaged by bowel or other surrounding structures with similar echogenicity. However, adnexal masses are frequently larger and very easy to identify with transabdominal imaging (Figure 12-4D).

Transvaginal Sonography

Transvaginal scanning is different from other ultrasound techniques because the ultrasound probe is placed inside the vagina and very close to the organs of interest. Transvaginal sonography is accomplished using a specialized probe with a 5–7.5 MHz transducer. The probe has an indicator, similar to other ultrasound probes, which should correlate to the left side of the monitor screen. The sound beams may emanate straight out from the tip of the probe (end-fire) or at an angle from the tip of the probe (offset). End-fire probes are more versatile and make imaging planes easier to understand. This discussion of scanning planes will assume that an end-fire probe is being used.

Before the transvaginal probe is used, it must be thoroughly cleansed and covered by a rubber or vinyl sheath. Conducting gel should be placed inside the sheath before the probe is covered for appropriate sound transmission. Most sonologists use specially made latex condoms as probe covers while some prefer to use vinyl gloves as probe covers.115 Water-based lubricant, not conducting gel, should be used to lubricate the outside of the sheath before insertion into the vagina. Ultrasound conducting gel may be irritating to the vaginal mucosa. Patients should empty their bladder before transvaginal scanning is performed. A full bladder will straighten the angle between the uterus and vagina and move the body of the uterus away from the probe. Patient positioning is important in obtaining good transvaginal scans. The operator must be able to aim the probe anterior enough to see the fundus of an anteverted uterus. Scanning is best accomplished while the patient is in lithotomy stirrups or by elevating her pelvis on a pillow while she is in a frog-leg position. Many clinicians prefer to use lithotomy stirrups and perform transvaginal sonography as part of their pelvic examination, after the speculum and bimanual examinations.

Before inserting the transvaginal probe, the procedure should be explained to the patient. It is usually best to explain that transvaginal sonography is similar to the bimanual pelvic examination but visual rather than tactile information is obtained. Transvaginal sonography should not be painful and is usually very well tolerated by patients. Anxious patients may be given the option of inserting the probe into the vagina themselves.

The probe is initially inserted with the probe indicator pointed toward the ceiling (Figures 12-6 and 12-7). The uterus is easily recognized upon insertion of the probe. This is the standard transvaginal sagittal view; it produces a longitudinal image of the uterus similar to the transabdominal sagittal view but rotated 90 degree counterclockwise (Figure 12-8). The entire uterine midline stripe should be seen in this view. If the uterus is not seen immediately, then it may be extremely anteverted and the probe should be aimed upward toward the anterior abdominal wall, keeping the indicator pointed toward the ceiling. Lateral movement of the probe can be used to scan from side to side through the entire pelvis (Figure 12-6). The uterus appears as a relatively hypoechoic structure with thick walls and a well-defined border. The endometrial midline stripe is thin during the proliferative phase and thick during the secretory phase of the menstrual cycle (Figures 12-9 and 12-10). The cervix can be seen by pulling the probe back a few centimeters and aiming the probe tip downward toward the patient's back (Figure 12-11). In this view, the posterior cul-de-sac should be inspected for any evidence of free fluid.

After the uterus is identified, the ovaries can be found by their position relative to the uterus. They are usually found just lateral and posterior to the body of the uterus, between the uterus and the lateral pelvic wall. The sonographic appearance of the ovaries is distinct. They are relatively hypoechoic structures containing multiple anechoic follicles (Figures 12-12, 12-13, and 12-14). To find the ovaries in sagittal oblique planes, the probe is aimed laterally, with the probe indicator still toward the ceiling (Figure 12-6). The internal iliac artery and vein can often be identified and used as a guide because the normal position of the ovary is adjacent to these structures. Sometimes the ovaries cannot be identified with transvaginal sonography.116

The standard transvaginal coronal view may be better for surveying the entire pelvis. This view is obtained by turning the probe indicator toward the patient's right side (Figures 12-15 and 12-16). The coronal view gives a transverse image of the uterus and allows the uterus and ovaries to be seen in the same plane. The entire pelvis can be explored with oblique coronal planes by aiming the probe up toward the anterior abdominal wall and down toward the patient's back, keeping the probe indicator pointing toward the patient's right side (Figure 12-17).

Transvaginal sonography is a dynamic imaging technique. To visualize structures, they need to be very close to the tip of the probe. When structures are not readily visualized, operators should use their free hand to palpate the patient's anterior abdominal wall, similar to performing a bimanual pelvic examination.30, 69, 115 Pressure on the anterior abdominal wall will often bring an ovary or a mass into the field of view. Also, the abdominal hand and the transvaginal probe can be used together to manipulate pelvic contents and observe how the organs move in relation to one another. An ovary may be easier to identify if it is seen as a discrete structure moving independently from adjacent loops of bowel. Also, structures that appear as complex masses may be comprosed of multiple smaller structures that move independently of each other. Holding the transvaginal probe very still and observing for bowel peristalsis is a good method for differentiating bowel from other pelvic structures. Finally, the tip of the transvaginal probe can be used to try to localize pelvic pain. This may help the physician narrow the differential diagnosis when a mass or other abnormality is visualized.

Although several standard imaging planes have been described, the pelvis can often be scanned without concern for specific planes. Once an organ or a mass is identified, the probe can be turned in any direction that helps the operator obtain better images. Also, as long as the entire pelvis is imaged in a systematic organized manner, the use of specific planes is probably not crucial.117

Normal Early Pregnancy

Both transvaginal and transabdominal sonography can be used to detect an early intrauterine pregnancy. Transvaginal ultrasound can identify an intrauterine pregnancy at about 5 weeks' gestational age (3 weeks postconception), about 7–10 days earlier than transabdominal ultrasound. The convention when referring to the age of a pregnancy is gestational age, which is the date from conception plus 2 weeks. An approximate correlation can be made between gestational age, β-hCG level, and pelvic ultrasound findings (Table 12-1).4, 30, 53, 69, 118–124

Transvaginal sonography is now the standard modality for evaluating early pregnancy. The following descriptions pertain to transvaginal sonography, except where specifically noted. The transvaginal technique is referred to as “endovaginal” sonography by some authors. The first sonographic sign of early pregnancy, the intradecidual sign, can be seen at 4–5 weeks (Figure 12-18). The intradecidual sign is a small sac, only a few millimeters in diameter, which is completely embedded within the endometrium on one side of the uterine midline, not deforming the midline stripe.30, 124, 125 There is a focal echogenic thickening of endometrium surrounding the sac. The intradecidual sign can be seen only by using a high-resolution technique (5 MHz or higher) and is not an accurate indicator of intrauterine pregnancy.125

A gestational sac can be clearly identified at about 5 weeks. With transvaginal sonography, a gestational sac can be seen in most patients with β-hCG levels of 1,000–2,000 mIU/mL and in all patients with levels above 2,000 mIU/mL.123 A gestational sac is characterized by a sonolucent center (chorionic sac) surrounded by a thick symmetric echogenic ring, known as the chorionic rim. This finding is seen in most intrauterine pregnancies but can also be seen surrounding a pseudogestational sac associated with an ectopic pregnancy.69 Doppler ultrasound can be used to measure peritrophoblastic flow in order to distinguish a true gestational sac from a pseudogestational sac.126 However, since this is outside the realm of bedside emergency sonography, identification of a simple gestational sac should not be used as definitive evidence of an intrauterine pregnancy.

Many authors consider a clear double decidual sign as the first definitive evidence of an intrauterine pregnancy.30, 69, 127 The double decidual sign is two concentric echogenic rings surrounding a gestational sac (Figure 12-19). The inner ring is the same structure as the chorionic ring and is called the decidua capsularis. The outer ring is called the decidua vera, derived from the stimulated endometrium of the uterus, while the thin hypoechoic layer between them is the endometrial canal.30, 127, 128 A gestational sac with a vague or an absent double decidual sign is not diagnostic of an intrauterine pregnancy and may be a pseudogestational sac. If two clear rings are seen, an intrauterine pregnancy is very likely. Unfortunately, the double decidual sign is present in only about half of all intrauterine pregnancies and is not 100% accurate.129

The yolk sac is the first structure that can be seen inside the gestational sac (Figure 12-20). Some authors consider the yolk sac the first definitive evidence of intrauterine pregnancy.53, 124 It is probably prudent for inexperienced sonologists to visualize the yolk sac before making a diagnosis of an intrauterine pregnancy, avoiding misinterpretation of more subtle findings like the double decidual sign. The yolk sac is a symmetric circular echogenic structure at the edge of the gestational sac. The yolk sac has a role in the transfer of nutrients to the embryo during the first trimester and early hematopoiesis takes place there. The yolk sac can first be seen by transvaginal sonography at about 5–6 weeks and then shrinks and disappears by about 12 weeks.130

The embryo appears as a thickening or small mass that is seen at the margin of the yolk sac between 5 and 6 weeks Figure 12-21A). The normal embryo will grow rapidly, about 1 mm per day. The embryo can first be seen when it is only 2–3 mm and cardiac activity may not be detectable initially. By 6 weeks, the embryo is a distinct structure separate from the yolk sac (Figure 12-21B). Also, the tiny vitelline duct, which connects the yolk sac to the base of the cord, can sometimes be seen between the yolk sac and the embryo.

Cardiac activity should be detected within the embryo at about 6 weeks. Any embryo measuring greater than 5 mm should have cardiac activity when transvaginal sonography is used. At 7 weeks, the embryo will be about 12 mm and the head of the embryo will be clearly distinguished. At this age, the embryo's head contains a single large cerebral ventricle and has an appearance similar to the yolk sac.69 At 8 weeks, the head of the embryo is about the same size as the yolk sac and limb buds begin to appear (Figure 12-22). Also, the physiologic midgut herniation can be visualized as an echogenic mass anterior to the trunk of the embryo. The bowel becomes intra-abdominal and the hernia disappears by 12 weeks. At 8 weeks and beyond, a thin echogenic line, the amnionic sac, may be seen surrounding the embryo.

At 10 weeks, organogenesis is complete and the embryo is now referred to as a fetus (Figure 12-23). Between 10 weeks and the end of the first trimester, the contours of the fetus become much more obvious. The fingers and toes can be identified and counted. Limb movements can be observed and bones and joints can be recognized. In the head, the falx cerebri becomes very distinct and the prominent choroid plexus can be seen in each of the lateral ventricles. The kidneys and bladder can be evaluated at 12 weeks. The heart and the stomach can also be identified inside the trunk and a four-chamber heart can be recognized by the end of the first trimester. Finally, the face and palate can be easily recognized late in the first trimester.

Routine screening for fetal abnormalities is not typically performed during the first trimester; the optimal time for this is at 18–20 weeks. However, some obvious abnormalities may be identified and it is important to know which structures are usually seen during the first trimester. There is some utility to evaluating nuchal thickness with transvaginal sonography, between 11 and 14 weeks, as a screening test for exomphalos and trisomies 18 and 13, but this is outside the realm of emergency bedside sonography.

Pregnancy Dating

Measurements of both the gestational sac and the embryo are accurate in the first trimester. Tables and formulas are available for calculating the gestational age using these measurements.4, 131 However, modern ultrasound software automatically calculates gestational age when calipers are placed on the structures of interest and appropriate presets are used.

The earliest measurement that can be used for pregnancy dating is mean sac diameter (MSD) of the gestational sac. MSD is the average of three orthogonal measurements of the gestational sac: (length + width + depth)/3. Pregnancy dating using MSD is only useful at 5–6 weeks, when the gestational sac is present but an embryo is not yet seen.

When an embryo is visible, at about 6 weeks, measurement of the crown-rump length (CRL) of the embryo should be used to date the pregnancy.53 When measuring CRL, it is important to measure the maximal embryo length, excluding the yolk sac (Figure 12-24). Errors can occur when the calipers are not carefully placed at the margins of the embryo. Also, the embryo can flex and extend slightly, changing the measurement. Nevertheless, gestational age determination by CRL is accurate to within 5–7 days.30

Measurement of the biparietal diameter (BPD) of the fetal skull is used for pregnancy dating at the end of the first trimester and during the second trimester. The BPD is a transverse measurement of the diameter of the skull at the level of the thalamus. The calipers should be positioned from the leading edge of the skull (outer table) on the near side to the leading edge of the skull (inner table) on the far side (Figure 12-25). Errors can be made by measuring the wrong part of the skull or if the image plane is not a true transaxial section through the fetal head. Pregnancy dating by BPD is also very accurate, especially prior to 20 weeks.69

Multiple Pregnancy

Documentation of the chorionicity and amnionicity of a multiple pregnancy is important early in the pregnancy because it may be hard to determine later in pregnancy. There are several sonographic criteria that can be used to determine chorionicity and amnionicity in the first trimester. Two clear gestational (chorionic) sacs may be seen as early as 6 weeks; this is good evidence of dichorionic twins (Figure 12-26). Later in the first trimester, dichorionicity can be established by finding a thick septum separating the two chorionic sacs (Figure 12-27). If the septum separating the two pregnancies is thin, then it may be difficult to determine whether it is the wall of a chorionic sac or an amnionic membrane. When the septum is thin, identification of a chorionic peak can confirm a dichorionic twin pregnancy. A chorionic peak is a triangular projection of tissue, of the same echogenicity as the placenta, emanating from the placenta and tapering to a point in the intertwin membrane.30

The amnionicity of a monochorionic pregnancy can also be determined by first trimester sonography. Counting the number of yolk sacs is the easiest way to determine amnionicity; if there are two yolk sacs, then there must be two amnions.69 After about 8 weeks, amnionic membranes should be visible and diamnionic pregnancies should have a separate amnion surrounding each twin.

Ectopic Pregnancy

Definite Ectopic Pregnancy

A live extrauterine embryo with cardiac activity can be seen with transvaginal sonography in up to 15–20% of ectopic pregnancies (Figure 12-28).54, 58 An extrauterine gestational sac containing an embryo or yolk sac is also diagnostic and is seen in a significant percentage of ectopic pregnancies (Figure 12-29).58

Nonspecific Signs of Ectopic Pregnancy: Free Fluid, Tubal Ring, and Complex Mass

There are several nonspecific sonographic findings that are not diagnostic but are highly suggestive of an ectopic pregnancy in pregnant patients with an empty uterus (Table 12-2).26, 54, 56–59, 132–134 Some of these findings are subtle and may be easily missed, especially if transvaginal sonography is not available or an inexperienced sonologist performs the scan. Therefore, emergency physicians should obtain a comprehensive ultrasound examination if no intrauterine pregnancy or ectopic pregnancy is identified with emergency bedside sonography.

Free Pelvic or Intraperitoneal Fluid

Free fluid in the posterior pelvic cul-de-sac or in other intraperitoneal sites is suggestive of ectopic pregnancy (Figure 12-30).56, 59, 134, 135 Transvaginal sonography is very sensitive for detecting free fluid in the posterior cul-de-sac.30 Only about one third of ectopic pregnancies have no free fluid in the cul-de-sac.136 Also, free fluid is the only abnormal sonographic finding in about 15% of ectopic pregnancies.134 The greater the volume of free intraperitoneal fluid, the greater the likelihood of ectopic pregnancy (Figures 12-31 and 12-32).69, 135 In fact, patients with a moderate to large amount of free pelvic fluid have about an 86% chance and those with hepatorenal free fluid have a nearly 100% chance of having an ectopic pregnancy.59 Although a large amount of fluid predicts ectopic pregnancy, it is not a reliable indicator of tubal rupture. Only about 60% of those with a large amount of free fluid have a ruptured tube.56, 137 Free fluid may be due to leaking of blood from the end of the fallopian tube, which can occur slowly.

Echogenic fluid is more likely to represent blood, and this also increases the chances of an ectopic pregnancy (Figure 12-30). If bleeding is brisk, clots may be seen in the pelvic cul-de-sac instead of fluid. Although a small amount of hypoechoic free pelvic fluid may be normal, it must be considered suspicious in the setting of a pregnant patient with an empty uterus.56, 57, 59, 134 The definition of “small amount” is fluid that is confined to the cul-de-sac and covering less than one third of the inferior posterior uterus. As stated, anything more than a small amount is almost always associated with an ectopic pregnancy.56, 58, 59

Abdominal sonography of the hepatorenal space (Morison's pouch) should be performed on every patient with a possible ectopic pregnancy.30, 69 Free fluid in the hepatorenal space (Figure 12-33), or elsewhere outside the pelvis, is evidence of a large amount of intraperitoneal fluid.138 In a pregnant woman with an empty uterus, this must be considered bleeding secondary to an ectopic pregnancy. Finding free fluid in the hepatorenal space with emergency bedside sonography reduces the time to diagnosis and treatment of ectopic pregnancy.6 A finding of hepatorenal free fluid “should give the surgeon a greater sense of urgency.”30

Tubal Ring

A tubal ring is nearly diagnostic of ectopic pregnancy.54, 58, 132, 134 A tubal ring is a concentric hyperechoic structure found in the adnexa (Figures 12-34, 12-35, and 12-36). It is created by the trophoblast of the ectopic pregnancy surrounding the chorionic sac and is the equivalent of a gestational sac.30 A tubal ring, in general, has a different sonographic appearance than a corpus luteum or other ovarian cysts because it has a relatively thick and brightly echogenic, round, symmetric wall. Ovarian cysts have walls of varying thickness and are surrounded by normal ovarian follicles. With transvaginal sonography, it may be possible to identify a tubal ring in more than 60% of ectopic pregnancies.54, 58 When a tubal ring is seen, the likelihood of ectopic pregnancy is greater than 95%.58

Complex Mass

The most common sonographic finding in ectopic pregnancy is a complex adnexal mass (Figures 12-37 and 12-38).52 A complex adnexal mass may represent a tubal hematoma, ectopic trophoblastic tissue, or distorted contents of an ectopic gestational sac.54, 58, 59, 69,133, 134 A complex mass contains a mixture of cystic and solid components. This is a sensitive sonographic sign of ectopic pregnancy. When an experienced sonologist performs a transvaginal scan, it may be seen in up to 85% of cases.58 However, a complex mass may be subtle and easily missed.69 The mass may blend into adjacent structures with similar echogenicity and may have an appearance similar to the bowel or ovaries.

Several sonographic signs may help differentiate a complex mass from the surrounding pelvic structures. Identifying the ovaries and then searching between the ovaries and the uterus is the best technique for locating an adnexal mass. To differentiate a mass from other pelvic structures, sonologists should press down on the patient's lower abdomen with their free hand during transvaginal scanning, in a manner similar to performing a bimanual pelvic examination. This will cause pelvic structures to move in relation to one another and examiners can recognize a mass as a separate structure, moving independently from the ovary and bowel. Also, if the transvaginal probe is held very still, peristalsis of the bowel can be seen, differentiating it from other pelvic structures.

Color Doppler has been used in an attempt to differentiate surrounding structures from an adnexal mass. High velocity, low impedance trophoblastic flow can sometimes be seen surrounding an ectopic sac; this is referred to as the “ring of fire”139 (Figure 12-39). Although some authors suggest that color Doppler provides little additional information and is not more accurate than grey-scale sonography for determining whether an adnexal mass is an ectopic pregnancy.30, 104, 140 More recent studies and case reports suggest asymmetric adnexal color Doppler flow is a useful clue.141, 142

Pregnancy Loss

Embryonic Demise

There are several sonographic signs that can reliably predict embryonic demise. The earliest sign is a gestational sac without a yolk sac or embryo (Figure 12-40). With high-resolution transvaginal sonography (≥ 6.5 MHz), a yolk sac is usually seen within the gestational sac when MSD is ≥ 10 mm and an embryo is usually seen when MSD is ≥ 16 mm.30, 121, 143, 144 However, with a 5 MHz transvaginal probe or with transabdominal scanning, a yolk sac may not be seen until the MSD is ≥ 20 mm.69, 145, 146 For the purposes of emergency bedside transvaginal sonography, an empty gestational sac ≥ 20 mm is a good predictor of embryonic demise; this is referred to as a blighted ovum. The nonobstetrics clinician should refrain from proclaiming this to the patient and simply note that normal structures are not seen and it may be too early to make a firm diagnosis.

Another good indicator of embryonic demise is lack of embryonic cardiac activity (Figure 12-41). With transvaginal sonography, cardiac activity should be seen in all embryos greater than 5 mm long by crown-rump length.30, 69, 96, 147 With transabdominal sonography, cardiac activity should be seen in all embryos greater than 10 mm long.69 When searching for embryonic cardiac activity, it is important to be sure that the embryo is clearly seen. This is easier at 7–8 weeks when the embryonic head and torso can be identified. Also, it is essential to use a high frame rate and turn off the frame-averaging mode when looking for cardiac activity.30

Several more subtle signs are also suggestive of embryonic demise or poor fetal outcome. Embryonic bradycardia predicts a poor prognosis148, 149 The normal heart rate for an embryo longer than 5 mm by crown-rump length (6.3 weeks' gestational age) is greater than 120 beats per minute (bpm). The lower the heart rate is below 120 bpm, the lower the survival rate of the embryo. Embryos longer than 5 mm with heart rates below 100 bpm have a survival rate of only 6%.149 Very early pregnancies, with embryos less than 5 mm in length, normally have slower heart rates, but a rate less than 90 bpm is nearly always associated with embryonic demise.148, 149

An abnormal yolk sac is another subtle sign of demise or abnormal pregnancy. A very small yolk sac (less than 2 mm diameter) between 8 and 12 weeks is usually associated with an abnormal pregnancy.150 A very large yolk sac (>6 mm diameter) between 5 and 12 weeks is predictive of embryonic demise or a significant chromosomal abnormality.30, 151 Also, prior to 12 weeks, inability to visualize the yolk sac when an embryo is clearly present is strong evidence of impending embryonic demise.151 Yolk sac shape is not associated with adverse pregnancy outcome. Pregnancies with a normal size but irregularly shaped yolk sac have a normal outcome in nearly all cases.30

An odd-shaped or grossly distorted gestational sac is reportedly a good indicator of pregnancy failure, but this finding is subjective (Figure 12-42).145 A gestational sac low in the uterus, with or without a yolk sac or embryo, is generally considered a sign of inevitable abortion (Figures 12-43 and 12-44). Also, a weakly echogenic or thin (<2 mm wide) trophoblastic reaction surrounding a gestational sac may indicate imminent demise. Finally, a gestational sac, which is not more than 5 mm MSD larger than the crown-rump length of the embryo, is probably abnormal.146, 152

Subchorionic hemorrhage is bleeding between the endometrium and chorionic membrane. This is a common finding late in the first trimester. Sonographically, part of the chorionic membrane and placenta are separated from the decidua vera (the endometrium) (Figure 12-45).30 Acutely, the hemorrhage may appear hyperechoic or isoechoic relative to the placenta, with only slight elevation noted. Over the next week or two, the blood becomes hypoechoic. Patients who present with threatened abortion and have a subchorionic hemorrhage probably have a higher incidence of embryonic demise.153, 154 Those with large subchorionic hemorrhages may have a much higher rate of pregnancy loss.153

Physicians should be conservative when interpreting findings of embryonic demise and give the pregnancy the benefit of the doubt in all cases. Ordering a comprehensive ultrasound and obtaining an obstetrics consult is prudent when the diagnosis is unclear.

Completed Spontaneous Abortion

The uterus should be empty after a completed spontaneous abortion (Figure 12-46). A small amount of blood or clot may also be present.

Retained Products of Conception

Patients with intrauterine echogenic material or a thickened midline stripe (≥10 mm wide) after a spontaneous abortion probably have retained products of conception (Figure 12-47).90, 92, 155 When curettage is performed in such cases, chorionic villi are identified in about 70%.92 Many patients with retained products will do well with expectant management but they may require curettage and should be followed closely for bleeding and infection.156

Several normal anatomic variants may make transabdominal and transvaginal pelvic sonography more difficult. Retroversion of the uterus occurs in about 10% of women. It has little clinical significance but it makes transabdominal imaging difficult. Retroversion means that the body of the uterus bends posterior toward the rectosigmoid colon instead of toward the anterior abdominal wall. The body of the uterus is then too far away from the transabdominal probe and resolution is poor (Figure 12-48A). Transvaginal sonography is much better for imaging a retroverted uterus because the probe can still be placed close to the body of the uterus (Figure 12-48B). When the uterus is retroverted, the ovaries usually lie anterior and lateral to the body of the uterus.

Lateral deviation of the uterus is another normal variant that makes pelvic ultrasound difficult. When transabdominal or transvaginal scanning is performed and the uterus is not seen in the midline, then the probe should be aimed laterally, and sagittal oblique images obtained. It is not uncommon to find the body of the uterus bending toward the lateral pelvis. If this is the case, then the midline stripe may be difficult to see in just one plane. Lateral and coronal images may be helpful in this situation. When the uterus is deviated laterally, it may displace the ovary out of its usual location. The ovary may then be found superior to the uterus or in the posterior cul-de-sac.

Variation in the location of the ovaries can also make pelvic ultrasound difficult. Transvaginal sonography is required to visualize most normal ovaries. Even with transvaginal scanning, however, they may be difficult to find. In women who have previously been pregnant, the ovaries may be found lateral, posterior, or superior to the uterus. In patients with an enlarged uterus, those who are pregnant or have uterine fibroids, the ovaries are often displaced superior to the uterus. When the ovaries are superior to the uterus, they are difficult to see with transvaginal sonography.

The fallopian tubes are not normally seen on transabdominal ultrasound ultrasound. If the tubes are filled with fluid secondary to scarring or pelvic inflammatory disease, then they may be easily recognized. They will be found in the adnexa lateral to the uterine body. When imaged longitudinally, the fallopian tubes will appear as anechoic tubal structures; when imaged transversely, they will appear as cystic structures. If multiple redundant loops of the tube are adjacent to one another, then this may be misinterpreted as a large multicystic mass. Using the endovaginal approach, healthy fallopian tubes are frequently imaged at their uterine origin and may be traced near each ovary if there is no bowel gas interference.

A small amount of fluid in the posterior cul-de-sac can be normal. This fluid may not be seen with transabdominal sonography but is easily visualized with transvaginal imaging (Figure 12-49).

Pelvic Masses

Corpus Luteum Cyst

Corpus luteum cysts are the most common pelvic masses found in early pregnancy. They are usually unilocular and have thin walls (Figure 12-50). Internal hemorrhage may result in internal septations and echogenic material (Figure 12-51). The corpus is solid in appearance in up to 50% of cases.

Leiomyomas

Uterine fibroids are very common and may grow during pregnancy. They are located in the uterine wall and have a variable sonographic appearance. They often cause dispersion of ultrasound and distortion of pelvic images (Figure 12-52).

Malignant Pelvic Masses

The most common tumors that enlarge during pregnancy are ovarian cystadenomas. Internal septations and papillary excrescences are suggestive of malignancy (Figure 12-53).

Adnexal Torsion

Most cases of adnexal torsion occur in the presence of an enlarged ovary or an ovarian mass (see Chapter 14). Finding a normal ovary makes the diagnosis much less likely.

Gestational Trophoblastic Disease

Most cases of GTD present as a benign molar pregnancy. Those with an invasive mole or choriocarcinoma usually have a history of a molar pregnancy. The classic finding is the appearance of a cluster of “grapes,” an intrauterine mass with diffuse hypoechoic vesicles (Figure 12-54). The appearance is not always classic in the first trimester, and the diagnosis may be missed (Figure 12-55).

Ectopic Pregnancy

1. Not performing pelvic sonography because of a recent last menstrual period or a low β-hCG. Patients with a positive pregnancy test who present with abdominal pain or vaginal bleeding should undergo a pelvic ultrasound examination regardless of their reported last menstrual period or β-hCG level. Patients may misinterpret vaginal spotting during pregnancy for a menstrual period; thus, obtaining a menstrual history is not an accurate method for excluding ectopic pregnancy. Also, it is not uncommon for patients to have a low β-hCG level and a ruptured ectopic pregnancy.

2. Attributing an empty uterus to a very early intrauterine pregnancy or a completed spontaneous abortion. More than 40% of ectopic pregnancies have a β-hCG level less than 1,000 mIU/mL; therefore, an empty uterus with a low β-hCG level should not be considered normal and the entire pelvis should be scanned for signs of an ectopic pregnancy.62 Also, the only definitive evidence of a completed spontaneous abortion is passage of obvious products of conception or chorionic villi. Without definitive evidence of a completed abortion, the diagnosis of ectopic pregnancy must be ruled out.46

3. Mistaking a pseudogestational sac for a gestational sac. Visualizing an intrauterine pregnancy essentially excludes the diagnosis of ectopic pregnancy in most patients. The intradecidual sign and gestational sac are early signs of an intrauterine pregnancy, but neither is 100% reliable.121, 124, 125 Sonologists should be careful not to mistake a pseudogestational sac associated with an ectopic pregnancy for a gestational sac.30, 69, 126 A pseudogestational sac, also known as a decidual cast, is an intrauterine fluid collection surrounded by a single decidual layer (Figures 12-36). A pseudogestational sac occurs in 5%–10% of ectopic pregnancies and appears as an elongated and odd-shaped sac in the center of the endometrial cavity with inconsistent thickening of the endometrium.69 A pseudogestational sac can usually be differentiated from a gestational sac using transvaginal sonography.100 Also, Doppler ultrasound may help by finding high-velocity low impedance peritrophoblastic flow surrounding a true gestational sac, but the reliability of this is not 100%.126, 139

4. Misidentifying an early intrauterine pregnancy. Clinicians should avoid making the diagnosis of an intrauterine pregnancy when only a small gestational sac is visible. A clear double decidual sign is the first reliable evidence of an intrauterine pregnancy.30, 127 A yolk sac and embryo are obvious signs of an intrauterine pregnancy and should be seen when an inexperienced sonologist makes the diagnosis of an intrauterine pregnancy.121 Cardiac activity should be seen in all embryos greater than 5 mm long, and this is regarded as the best evidence of an intrauterine pregnancy. It may be prudent for novice sonologists to see cardiac activity before diagnosing an intrauterine pregnancy.

5. Overestimating the ability to identify subtle signs of ectopic pregnancy. Although an empty uterus, free intraperitoneal fluid in the hepatorenal space, and free fluid in the pelvis are easy to identify, complex adnexal masses and tubal rings may be subtle. An experienced sonologist should repeat indeterminate bedside scans to look for these subtle signs.

6. Performing a transvaginal ultrasound without a transabdominal scan. The transabdominal pelvic view allows a broader view of the pelvis and may detect masses that are outside the field of view of the transvaginal probe and may be a helpful starting point in some patients. Also, the hepatorenal space should always be scanned to look for free intraperitoneal fluid.69 Some patients may have minimal symptoms and normal vital signs despite a ruptured ectopic pregnancy with a large amount of intraperitoneal blood.

7. Identifying a normal appearing pregnancy but not recognizing its location in relation to the uterus. An ectopic pregnancy may appear to be an intrauterine pregnancy if its extrauterine location is not carefully noted (Figure 12-56). Also, an interstitial ectopic pregnancy may appear to be intrauterine but careful imaging will reveal that it lies on the margin of the uterine wall and not in the intrauterine cavity. Transabdominal sonography will help clarify the big picture in cases of possible ectopic pregnancy.

8. Mistaking an interstitial pregnancy for an intrauterine pregnancy. An interstitial pregnancy may be mistaken for an intrauterine pregnancy.157 Interstitial pregnancies comprise about 2–5% of all ectopic pregnancies.69 Most ectopic pregnancies occur in the ampullary segment of the fallopian tube but interstitial ectopic pregnancies occur in the cornual region (Figure 12-57). They are partially enveloped by the myometrium. Because of the rich myometrial blood supply, an interstitial pregnancy can grow larger and rupture later than most ectopic pregnancies. When rupture occurs, intraperitoneal bleeding (potentially arterial) and vaginal bleeding may be brisk and profuse. Many of these patients exsanguinate and die before reaching the hospital. It may be difficult to identify an interstitial pregnancy because the gestational sac may be completely surrounded by the uterus. However, an interstitial pregnancy usually appears to be at the margin of the uterine wall rather than inside the uterine cavity.158 The eccentrically located gestational sac is surrounded by an asymmetric myometrial mantle with a free wall thickness usually less than 5–8 mm. The “interstitial line sign” is a fine echogenic line extending from the endometrial stripe to the interstitial gestational sac. This finding is diagnostic of an interstitial ectopic pregnancy. If the diagnosis is not made early, prior to rupture, up to 50% of patients may require a hysterectomy.69

9. Failure to identify heterotopic pregnancy. Failure to obtain a history of fertility medications or in vitro fertilization may lead to this pitfall. The risk of heterotopic pregnancy in such patients is as high as 1%, so finding an intrauterine pregnancy does not exclude the diagnosis of ectopic pregnancy. Also, patients without these risk factors may have a heterotopic pregnancy.33, 159 Therefore, it is prudent to scan the entire pelvis looking for free pelvic fluid or an adnexal mass, even after an intrauterine pregnancy has been identified.

Other Pitfalls

1. Fetal anomalies. Failure to diagnose fetal anomalies by ultrasound has recently become a significant source of malpractice litigation. To avoid this problem, patients should be informed that emergency bedside sonography is a focused examination only and is not designed to detect embryonic abnormalities.

2. Embryonic demise. Many potential pitfalls are associated with the diagnosis of embryonic demise. When poor resolution or poor quality scans are obtained, normal structures may not be visualized, leading to the errant diagnosis of a blighted ovum. Also, inability to identify embryonic cardiac activity can occur secondary to mistaking another structure for the embryo or using a frame-averaging ultrasound mode. These pitfalls can be avoided by positively identifying the embryo and by using a high frame rate setting when searching for embryonic cardiac activity. Before the diagnosis of embryonic demise is made, the pregnancy should be given the benefit of the doubt. Sonography by an experienced operator and consultation with obstetrics is prudent before the patient is informed of the definitive diagnosis.

3. Multiple Pregnancy. When twins are identified by bedside ultrasound, it is important to inform the patient that about 25% of twin pregnancies diagnosed in the first trimester will become singleton pregnancies by the second trimester.

4. Pelvic Masses. The most common pitfall when identifying a pelvic mass is neglecting to arrange close follow-up and informing the patient of the finding. Pelvic masses may enlarge during pregnancy and are usually incidental findings on pelvic sonography. Ovarian malignancy may rarely present during pregnancy.

5. Pelvic pain. Pelvic pain is a common complaint in early pregnancy. A common pitfall of using pelvic ultrasound in these patients is that the finding of an intrauterine pregnancy often ends the work-up for the etiology of the patient's symptoms. Once ectopic pregnancy is excluded, the patient's pelvic pain may be attributed to the pregnancy and diagnoses such as appendicitis or adnexal torsion may not be considered. Physicians should remember that appendicitis is relatively common in pregnancy and 20% of adnexal torsion occurs during pregnancy.

6. Gestational Trophoblastic Disease. Molar pregnancy is usually obvious on pelvic ultrasound. However, early in pregnancy, the findings may be subtle. Serum β-hCG will always be very high in GTD. A potential pitfall is assuming that this diagnosis is excluded because it is not seen on bedside ultrasound. Such patients need close follow-up and repeat ultrasound examinations.

Case 1

Patient Presentation

A 20-year-old woman, gravida 3, para 0, at about 3–6 weeks' gestation, because she was unsure of her last menstrual period, complained of several hours of heavy vaginal bleeding and low, central abdominal cramping. She denied any history of sexually transmitted disease, intrauterine device, ectopic pregnancy, or pelvic surgery. Previous pregnancies ended in early spontaneous abortions. She denied vomiting, fever, and urinary symptoms.

On physical examination, her blood pressure was 105/71 mmHg, heart rate, 87 beats per minute; respirations, 14 per minute; and temperature, as 36.8°C. She was in no distress. Her head, neck, pulmonary, cardiovascular, and back examinations were unremarkable. Abdominal examination revealed a soft abdomen with mild suprapubic tenderness. Speculum examination revealed a closed cervical os with a small amount of blood in the vaginal vault. Bimanual pelvic examination revealed no tenderness or mass.

Management Course

Urinalysis was unremarkable, but the urine pregnancy test was positive. Bedside transvaginal ultrasound performed immediately after the pelvic examination showed an empty uterus and a 3 × 3 × 4 cm right adnexal mass adjacent to the right ovary, containing a gestational sac, yolk sac, and embryo (Figure 12-58). Estimated gestational age by crown rump length was 6 weeks and 2 days. Trace free fluid was noted in the right adnexa, but the pouch of Douglas and Morison's pouch were negative for free fluid. Intravenous access was obtained, and the obstetrics service was consulted. The serum β-hCG level was 14,358 mIU/mL and the blood type was B positive. A repeat ultrasound examination in the radiology department confirmed the above bedside findings. The patient was taken to the operating room where a laparoscopic right salpingectomy was performed without complications. The patient recovered well and subsequently was discharged home.

Commentary

Case 1 was an example of a patient with an unruptured ovarian ectopic pregnancy. This diagnosis was made rapidly by the emergency physician using bedside transvaginal ultrasound immediately after the routine pelvic examination. This case demonstrated that the bimanual pelvic examination is unreliable for detecting significant pelvic pathology. Given the patient's serum β-hCG level greater than 10,000 mIU/mL and adnexal mass diameter of 4 cm, medical therapy with methotrexate would likely fail.

Case 2

Patient Presentation

A 36-year-old woman, gravida 2, para 1 at 11 weeks stated gestational age, presented to the emergency department via ambulance 15 minutes after the acute onset of painless vaginal bleeding. She reported that she had been dealing with multiple episodes of vomiting over the previous 5 days, which was unlike her previous pregnancy. She denied any other significant symptoms or medical history.

On physical examination, her blood pressure was 110/68 mmHg, heart rate, 110 beats per minute; respirations, 20 per minute; and temperature, 36.7°C. She appeared older than her stated age. Her head, neck, pulmonary, cardiovascular, and back examinations were unremarkable. Abdominal examination revealed a prominently gravid abdomen, noted to appear larger than expected for the patient's stated gestational age. Mild epigastric tenderness was present. Emergency department pelvic examination was deferred in consideration of vaginal bleeding and advanced gestational age.

Management Course

A urine pregnancy test was positive. The patient received intravenous fluids and an antiemetic. Bedside transabdominal pelvic ultrasound in the emergency department showed a “snowstorm” appearance with cystic structures within the uterus, concerning for gestational trophoblastic disease (Figure 12-59). Serum β-hCG measured 2,354,000 mIU/mL. The patient's blood type was A positive. The obstetrics service was consulted and a comprehensive ultrasound examination detailed an enlarged uterus filled with tissue and cysts consistent with complete molar pregnancy. The patient underwent a suction dilation and curettage. Her nausea and vomiting improved and she was discharged home on postoperative day #1 with plans for serial β-hCG measurements and clinic follow-up.

Commentary

Case 2 exemplified the utility of bedside ultrasound in the rapid diagnosis of pathologic conditions not routinely encountered in the emergency department. Recognition of normal and abnormal findings on bedside ultrasound helped focus the differential diagnosis. Although hyperemesis, a prominently gravid abdomen, and a markedly elevated serum β-hCG level were clues to this patient's final diagnosis, definitive diagnosis and management would not have taken place without ultrasound imaging.

Case 3

Patient Presentation

A 28-year-old woman arrived in the emergency department late in the evening, complaining of nausea, weakness, and episodic loss of consciousness over the past few hours. She did not know when her last menstrual period was. She felt confused, but denied any significant pain. She was unwilling to provide any further history, citing nausea and weakness.

Upon physical examination, her blood pressure was 82/40 mmHg, heart rate, 86 beats per minute; respirations were 22 per minute; and temperature was 36.9°C. The patient was diaphoretic and appeared uncomfortable. Her head, neck, pulmonary, and back examinations were unremarkable. Cardiac examination revealed a grade I/VI systolic murmur. Abdominal examination was significant for mild bilateral lower quadrant tenderness with no rebound or guarding. Genitourinary examination revealed a closed cervical os and no bleeding. She had mild cervical motion and bilateral adnexal tenderness.

Management Course

A urine pregnancy test was ordered as the emergency physician performed a transabdominal ultrasound examination. This revealed a hypoechoic sac in the uterus, a tubal ring in the left adnexa, and a small amount of free pelvic fluid (Figure 12-60). A scan of the upper abdomen revealed free fluid in the hepatorenal space. A urine pregnancy test was positive. After 2 L of intravenous normal saline, the patient's blood pressure was 94/52 mmHg with a heart rate of 84 beats per minute; infusion of O-negative packed red blood cells was initiated. The on-call obstetrician was immediately contacted and the operating room was prepared. While the obstetrician was en route, an emergency bedside transvaginal ultrasound examination confirmed a definite ectopic pregnancy with a yolk sac in the left adnexa. The patient was taken directly to the operating room when the obstetrician arrived. A ruptured ectopic pregnancy and 2–3 L of free intraperitoneal blood were found at surgery. The patient required a left salpingectomy. Her serum β-hCG level was 917 mIU/mL.

Commentary

Case 3 illustrated a patient with a ruptured ectopic pregnancy. She was in shock and required immediate resuscitation. She could not provide a reliable history and was not aware that she was pregnant. She had relatively mild abdominal symptoms and was not tachycardic, which is not uncommon with acute intraperitoneal blood loss. Transabdominal sonography revealed hepatorenal free fluid and a tubal ring. Hepatorenal free fluid alone, in a young pregnant woman with nontraumatic hypotension, is nearly diagnostic of a ruptured ectopic pregnancy and was enough evidence to proceed to surgery. In addition, this patient had a tubal ring, which is also nearly diagnostic of an ectopic pregnancy. Immediate bedside transvaginal scanning by the emergency physician allowed a more detailed view of the mass and revealed a definite ectopic pregnancy.