Chapter 13. Second- and Third-Trimester Pregnancy

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

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

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

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

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

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

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

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

What are the standard clinical indications for emergency ultrasound in the second and third trimesters of pregnancy? The concept that emergency ultrasound should remain focused, or goal-directed, helps define its appropriate use in the latter ...