Routine third-trimester ultrasound for the detection of small-for-gestational age in low-risk pregnancies (ROTTUS) study: a randomized controlled trial.

OBJECTIVE To compare in low-risk pregnancies the proportion of small-for-gestational-age (SGA) infants detected by routine third trimester ultrasound versus by selective ultrasound based on serial fundal height measurement (standard care). METHODS An open label randomised controlled trial was conducted at a hospital in Kenya. Low-risk pregnant women were randomly allocated to routine ultrasound for fetal growth between 36+0 and 37+6 weeks (routine ultrasound [intervention group]) or a selective growth scan as per clinically suspected on serial fundal height measurements (standard care [control group]). At ultrasound, fetal growth was assessed by abdominal circumference (AC) measurement. The main pre-specified outcome was the detection of SGA, defined as a birth weight < 10th centile. RESULTS Of the 566 eligible women, 508 (89.4%) were randomised (253 to the intervention and 255 to the control group). The detection rate of SGA infants of an AC<10th centile was 52.7% vs 7.7% (p<0.001) in the intervention and control groups, respectively. Specificity in the intervention group was 95.5% (191/200), and 98.5% (191/194) in the control group (p=0.08). The detection rate of an AC< 3rd centile was 66.7% vs 6.6% (p<0.001) in the intervention and control groups, respectively. Specificity in the intervention group was 91.7% (200/218), and it was 98.1% (205/209) in the control group (p=0.006). The area under the curve was significantly higher in the intervention group than in the control group (0.92 [95% CI 0.87-0.96]) vs. 0.68 [95%CI 0.58-0.77]); p<0.001). CONCLUSIONS In low-risk pregnant women, routine trimester ultrasound performed between 36-37 weeks is superior to selective ultrasound based on serial fundal height measurements for the detection of true SGA fetuses with high specificity. This article is protected by copyright. All rights reserved.