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

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.