Comparison of nuchal and detailed morphology ultrasound examinations in early pregnancy for fetal structural abnormality screening: a randomized controlled trial

Objective To compare the effectiveness of a nuchal scan at 10 to 14 + 6 weeks and a detailed morphology scan at 12 to 14 + 6 weeks in screening for fetal structural abnormalities. Methods From March 2001 to November 2004, 8811 pregnant women were randomized into either the control group (10 to 14 + 6‐week nuchal scan followed by routine 16–23‐week scan) or the study group (10 to 14 + 6‐week nuchal scan and 12 to 14 + 6–week detailed scan followed by routine 16–23‐week scan). Results We analyzed 7642 cases of singleton pregnancies with viable fetuses at first‐trimester ultrasound examination and with known pregnancy outcome. In the control group, the detection rate of structural abnormalities in the first trimester was 32.8% (21/64; 95% CI, 21.6–45.7%) and the overall detection rate was 64.1% (41/64; 95% CI, 51.1–75.7%). In the study group, the detection rate in the first trimester was 47.6% (30/63; 95% CI, 34.9–60.6) and the overall detection rate was 66.7% (42/63; 95% CI, 53.7–78.0%). The overall detection rate in the control group did not differ significantly from that in the study group (P > 0.05). Conclusions When the nuchal scan is offered, a basic anatomical survey can be done in conjunction with nuchal translucency thickness measurement. A detailed ultrasound examination at this early gestational age may not be superior to the nuchal scan in screening for fetal abnormalities in the low‐risk population. Though a wide range of abnormalities can be detected at 10 to 14 + 6 weeks, the routine 16–23‐week scan cannot be abandoned. Copyright © 2008 ISUOG. Published by John Wiley & Sons, Ltd.