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A 26-year-old woman gravida 3, para 2-0-0-2 with a singleton pregnancy at 27 weeks' gestation is concerned because her sister had a fetal demise and she thinks her baby is moving less. An ultrasound demonstrating normal anatomy (Figures 79-1, 79-2, and 79-3) and strong fetal heart motion is very reassuring (Figure 79-4).

Figure 79-1

Ultrasound examination of a 27-week estimated gestational age (EGA) fetus showing measurement of the baby's humerus. (Courtesy of E.J. Mayeaux, Jr., MD.)

Figure 79-2

Ultrasound examination of a 27-week EGA fetus showing the baby's stomach (St), abdomen, spine (SP), and left portal vein (PV). (Courtesy of E.J. Mayeaux, Jr., MD.)

Figure 79-3

Ultrasound examination of a 27-week EGA fetus showing measurement of the baby's biparietal diameter (BPD). (Courtesy of E.J. Mayeaux, Jr., MD.)

Figure 79-4

Ultrasound examination of a 27-week EGA fetus showing all four chambers of the baby's heart. (Courtesy of E.J. Mayeaux, Jr., MD.)

Ultrasound usage in the third trimester of pregnancy is most often utilized to determine fetal number, presentation, and growth issues. This later pregnancy scan is also used to document fetal cardiac activity, placental location, and amniotic fluid volume, as well as provide a method for antenatal fetal assessment.

  • A Cochrane review of 7 studies showed no difference in obstetric, antenatal, or neonatal interventions between women undergoing routine late ultrasound examination after 24 weeks and those who did not.1 In addition, there was no difference in perinatal outcome measures, such as admission to a neonatal intensive care unit, birthweight less than 10th percentile, or perinatal mortality.
  • Hydrops fetalis is the accumulation of fluid in fetal tissues and body cavities, usually a result of immune pathologic conditions (Figure 79-5). Serial ultrasound examinations are useful for following pregnancies at risk for developing hydrops or to evaluate treatment. As well as utilizing middle cerebral artery peak-systolic velocity as a noninvasive tool to predict fetal anemia.2
  • Ultrasound may also be used to evaluate third trimester bleeding. The major placental causes of vaginal bleeding at this time are placenta previa (Figure 79-6) and abruptio placentae.
  • Ultrasound can safely image maternal abdominal organs during pregnancy. Ovarian cysts, uterine leiomyoma, renal obstruction, and gallbladder or liver disease can be evaluated without using ionizing radiation.

Figure 79-5

Ultrasound examination showing scalp edema (E) associated with hydrops fetalis. (Courtesy of E.J. Mayeaux, Jr., MD.)

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