Fetal growth ultrasound in obese patients for the detection of growth abnormalities.

Abstract

To examine the impact of maternal obesity on fetal growth abnormalities including fetal growth restriction (FGR) and large for gestational age (LGA) fetuses. Secondary analysis from the Nulliparous Pregnancy Outcomes Study: Monitoring Mothers-to-be (nuMoM2b). The study excluded individuals with pregestational or gestational diabetes, chronic hypertension, and other major maternal medical conditions. Ultrasound assessments were performed at 16 - 21 and 22 - 29 weeks of gestation. Our exposure was the presence of pre-pregnancy obesity. Our primary outcome was rates of fetal growth abnormalities identified by ultrasound, defined as FGR (estimated fetal weight [EFW] or abdominal circumference < 10th percentile) or LGA (EFW > 90 th percentile) among obese compared to non-obese women. A secondary analysis was performed after limiting ultrasound performed from 28-29 weeks. To estimate adjusted relative risks (aRR) with 95% confidence intervals (95%CIs), we used generalized linear models with Poisson distribution and log link using robust error variance, adjusting for the predefined covariates. Of 7,354 participants, 1,443 (19.6%) had pre-pregnancy obesity while 5,911 (80.4%) did not. Pre-pregnancy obesity compared with normal weight was associated with an increased risk of fetal growth abnormalities both at 16-21 weeks (16.0% vs. 13.2%; aRR 1.23; 95%CI 1.06-1.42) and 22-29 weeks (16.0% vs. 12.1%; aRR 1.33; 95%CI 1.14-1.54). Furthermore, pre-pregnancy obesity compared with normal weight was associated with an increased risk of LGA both at 16-21 weeks (12.5% vs. 10.3%; aRR 1.24; 95%CI 1.05-1.47) and 22-29 weeks (10.6% vs. 6.9%; aRR 1.66; 95%CI 1.38-2.01). In a secondary analysis limited to the ultrasound 28-29 weeks, both fetal growth abnormalities and LGA were associated with the presence of obesity. In any of the analyses, pre-pregnancy obesity was not associated with FGR compared to normal weight. Maternal obesity is associated with an increased risk of fetal growth abnormalities and LGA fetuses.