Q: I am in the fourth month of my first pregnancy and my obstetrician would like to schedule ultrasound screening (ultrasonography) of the fetus. I am hesitant to have this procedure done because of the experience of my sister, whose initial ultrasonography showed a reduced amount of fluid surrounding the fetus. She eventually had a perfectly normal, full term baby, but only after months of needless worry and the expense of frequently repeated ultrasonography. How necessary is it for me to have an ultrasound examination?
A: Ultrasound screening of the fetus is a safe and effective way to assess fetal age and to detect problems such as abnormalities of the fetus or placenta, disorders of fetal growth and the presence of more than one fetus. Ultrasonography is strongly indicated for women with diabetes mellitus, chronic kidney disease or high blood pressure and in those with other disorders or situations that increase the risk of the pregnancy to either the mother or the fetus. Although many obstetricians recommend routine ultrasonography during pregnancy, a study recently published in the New England Journal of Medicine raises doubts about the value of this approach in women at low risk for fetal death or problems in the perinatal period (first 28 days after birth).
In this study, about 15,000 low-risk, pregnant women were randomly assigned to either an ultrasound-screening group or a control group. The former group underwent ultrasonography at both 15 to 22 weeks and 31 to 35 weeks of pregnancy. Women in the control group had ultrasonography only if their doctors identified a medical indication for the procedure. The average number of sonograms in the control group was 9.6 per woman, and 55 percent of them had no sonogram.
There was no difference between the two groups in the rate of fetal death, or death or serious complications in the perinatal period. However, three times more major fetal anomalies were detected in the ultrasound-screening group than in the control subjects, and some women have elected to have ultrasonography in order to be reassured that they will not give birth to a malformed baby.
The study suggests that ultrasonography is not essential if you are at low risk and your doctor does not later identify some factor that may place the fetus at excessive risk.
Dr. Margolis is professor of medicine and biological chemistry at the Johns Hopkins School of Medicine.