Association between maternal pre-pregnancy BMI category and fetal umbilical artery pH

Abstract

To evaluate the association between maternal pre-pregnancy body mass index (BMI kg/m2) and fetal umbilical arterial pH at the time of delivery in nulliparous women. We performed a secondary analysis of the nuMoM2b study. Subjects in this study were nulliparous with a singleton pregnancy. Subjects with fetal anomalies or missing fetal umbilical artery pH were excluded. Subjects were categorized based on pre-pregnancy BMI (less than 18.5, 18.5-24.9, 25-29.9, 30-34.9, 35-39.9, and 40 or greater). Our primary outcome was an umbilical artery pH at the time of delivery. We also examined base deficit, the rate of fetal acidosis defined as pH < 7.0, and the need for advanced neonatal resuscitation. Analyses were stratified by the route of delivery. Multivariable linear or logistic regression models were used to calculate adjusted P-values or adjusted odds ratios (95% confidence intervals), controlling for confounders. Of 3,015 subjects, 1,870 (62%) had a vaginal delivery, and 1,145 (38%) had a cesarean delivery. There were significant differences in demographics across the BMI categories in both subjects who had a vaginal delivery and cesarean delivery (age, race, chronic hypertension, gestational diabetes, pregestational diabetes, preeclampsia, and gestational hypertension). Among subjects who had a vaginal delivery, there was no difference in fetal umbilical artery pH (p=0.31) across the BMI categories (Table 1). Base deficit of subjects with BMI < 18.5 and BMI 40 or greater was significantly lower than that of subjects with BMI 18.5-24.9 (adjusted p< 0.05). Among subjects who had a cesarean delivery, the fetal umbilical arterial pH of subjects with BMI 30-34.9 and BMI 40 or greater was significantly lower than that of subjects with BMI 18.5-24.9 (adjusted p< 0.05) (Table 2). In nulliparous subjects with a singleton pregnancy, obesity was associated with decreased fetal umbilical arterial pH at the time of cesarean delivery. However, this finding was not observed in subjects who had a vaginal delivery.View Large Image Figure ViewerDownload Hi-res image Download (PPT)