Routine Ultrasound at 30th–33rd weeks versus 30th–33rd and 35th–37th weeks in Low-Risk Pregnancies: A Randomized Trial

Abstract

Introduction: The aim of this study was to evaluate the accuracy of 35–37 weeks’ ultrasound for fetal growth restriction (FGR) detection and the impact of 30th–33rd weeks versus 30th–33rd and 35th–37th weeks’ ultrasound on perinatal outcomes. Methods: This was a randomized controlled trial that enrolled 1,061 low-risk pregnant women: 513 in the control group (routine ultrasound performed at 30th–33rd weeks) and 548 in the study group (with an additional ultrasound at 35th–37th weeks). FGR was defined as a fetus with an estimated fetal weight (EFW) below the 10th percentile. p values < 0.05 were considered statistically significant. Results: The ultrasound at 35–37 weeks had an overall accuracy of FGR screening of 94%. Spearman’s correlation coefficient between EFW and birthweight centile was higher for at 35–37 weeks’ ultrasound (ρ = 0.75) compared with 30–33 weeks’ ultrasound (ρ = 0.44). The study group had a lower rate of operative vaginal deliveries (24.4% vs. 39.3%, p = 0.005) and cesarean deliveries for nonreassuring fetal status (16.8% vs. 38.8%, p < 0.001). Discussion/Conclusion: A later ultrasound (35–37 weeks) had a high accuracy for detection of FGR and had a higher correlation between EFW and birthweight centiles. Furthermore, it was also associated with lower adverse perinatal outcomes compared to an earlier ultrasound.