Chapter 17: Second and Third Trimester Pregnancy

INTRODUCTION

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 robust. 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 many parts of the examination are not relevant in the emergency setting, there are some findings that may be critical to the acute care of an obstetric patient. This chapter discusses the use of point-of-care ultrasound (POCUS) to evaluate pregnant patients in their second and third trimesters. During this time period, the major indications for its use are in the initial assessment of vaginal bleeding, labor, trauma, and 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 the assessment of cervical length and fetal position, and for the evaluation of traumatic and nonobstetrical causes of abdominal pain.

CLINICAL CONSIDERATIONS

In early pregnancy, POCUS is commonly used to help rule out ectopic pregnancy by confirming an intrauterine pregnancy. The clinical indications for POCUS in early pregnancy, the limited information sought, and the recommended technique are widely agreed upon and well described (see Chapter 16, “First Trimester Pregnancy”). In contrast, the role of POCUS in the second and third trimesters of pregnancy is not as well established. Yet, emergency care providers are frequently faced with evaluating patients who are in the latter part of pregnancy and present to the emergency department (ED) with trauma, vaginal bleeding, or abdominal pain. Depending on the practice setting, obstetrical consultation may not be readily available and patients may not have had prenatal care. Increasingly, POCUS is readily available in the emergency setting and clinicians are adept at its use. There are clearly a number of clinical situations during the second and third trimesters of pregnancy where a rapid, goal-directed ultrasound examination can expedite the diagnosis and improve the care of mother and fetus.

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

1. What are the clinical indications for POCUS in the second and third trimesters of pregnancy?

2. Which focused ultrasound applications are reasonable for acute care providers to perform during late pregnancy?

3. What are the goals of the POCUS in the second and third trimesters of pregnancy?

4. Is ultrasound safe, and what are the alternative diagnostic modalities in pregnancy?

What are the clinical indications for POCUS in the second and third trimesters of pregnancy? The concept that POCUS should remain goal-directed helps define its appropriate use in the latter part of pregnancy. In this setting, the focused concept takes on particular importance ...