A randomized trial of prenatal ultrasonographic screening: Impact on the detection, management, and outcome of anomalous fetuses

Objective: The objective of this randomized clinical trial was to test the hypothesis that ultrasonographic screening would significantly alter perinatal outcome as a result of the antenatal detection of fetal congenital malformations. Study Design: Pregnant women without a specific indication for ultrasonography were randomly assigned to have either two screening sonograms (15 to 22 weeks and 31 to 35 weeks) or conventional obstetric care with ultrasonography used only as determined by the clinical judgment of the patient's physician. The frequency of birth defect detection in the screened and control populations was compared, as was the impact of discovery on pregnancy outcome. Results: Major congenital malformations occurred in 2.3% of the 15,281 fetuses and infants in this study. Antenatal ultrasonography detected 35% of the anomalous fetuses in the screened group versus only 11 % in the control population (relative detection rate 3.1; 95% confidence interval 2.0 to 5.1). Ultrasonography screening did not, however, significantly influence the management or outcome of pregnancies complicated by congenital malformations. Specifically, only 9 abortions were performed for anomalies among 7685 fetuses in the screened group whereas 4 pregnancies were terminated for fetal anomalies detected among 7596 control subjects. Ultrasonography screening also had no significant impact on survival rates among infants with potentially treatable, life-threatening anomalies despite the opportunity to take precautionary measures such as delivery in a tertiary center. Conclusions: Ultrasonography screening in a low-risk pregnant population had no significant impact on the frequency of abortion for fetal anomalies. Survival rates for anomalous fetuses were also unaffected by screening.