Parameters for Ultrasound Exams in Pregnant Women

Question

What are the parameters for ultrasound exams in pregnant women? A patient has requested an ultrasound exam at each prenatal visit on the basis that a friend in Europe had one done at every prenatal visit.

Response From Expert

Karen L. Koscica, DO
Department of Obstetrics & Gynecology and Women's Health, Albert Einstein College of Medicine/Montefiore Medical Center, Bronx, New York

The question of the frequency of ultrasound examinations in pregnancy has been debated at length. There are many indications for sonography during pregnancy, but routine screening remains controversial. Routine screening implies that the procedure is performed in a low-risk population, or in those without a specific clinical indication, in order to detect potential problems. In pregnancy, the reason most often cited for routine ultrasound is to detect fetal anomalies, and this ultrasound examination is normally performed at approximately 18-20 weeks gestational age.

There have been several trials of routine ultrasound examinations during pregnancy. The largest, a prospective, randomized one of routine vs indicated ultrasound examinations, was the RADIUS study.^[1] This study included 15,530 pregnant women. One group underwent routine ultrasound at 15-22 weeks and again at 31-35 weeks. The other group underwent ultrasound only if a specific indication arose, such as uncertain dating or positive triple screen. The primary outcome measure was adverse perinatal outcome (fetal or neonatal death or moderate or severe neonatal morbidity). The secondary outcomes were multiple gestations, birthweight, and incidence of preterm delivery.^[1]

This trial found no difference in perinatal outcome between the groups. There was, however, a 3-fold increase in the detection of fetal anomalies, which did not have an effect on perinatal outcome, the investigators' primary outcome variable. Therefore, they concluded that, "The adoption of routine ultrasound screening in the United States would add considerably to the cost of care in pregnancy, with no improvement in perinatal outcome."^[1]

A critical analysis of the study reveals that the patients were primarily low-risk patients being seen in private offices. In reality, 60% of the potential population was excluded for high-risk conditions for which ultrasound examinations were deemed necessary, and then 45% of the control population subsequently developed an indication for an ultrasound examination. Thus, the vast majority of patients underwent ultrasound. Of significant concern is that only 17% of fetal anomalies were detected with ultrasound. This raises a question of quality of the ultrasound examinations being performed.^[2,3] Additionally, any cost/benefit analysis needs to include the cost of care of infants with birth defects and the expenses saved if pregnant women choose to terminate a pregnancy with a significant anomaly. The cost of routine screening may be less than the cost of support for newborns with major anomalies.^[3]

The main indications for routine ultrasound are to detect fetal anomalies, confirm pregnancy dating, and diagnose multiple gestations. Studies are still needed to demonstrate the cost-effectiveness of this intervention. The advantages must be weighed against the false positives and false negatives of the test. Although ultrasound has become standard of care in many settings, the routine use of this test is not universally accepted.

Medscape Ob/Gyn. 2002;7(2) © 2002  Medscape

Cite this: Peter S Bernstein, Karen L Koscica. Parameters for Ultrasound Exams in Pregnant Women - Medscape - Sep 25, 2002.