The association of maternal obesity with fetal pH in parturients undergoing cesarean delivery under spinal anesthesia

Objective: The aim of this study was to examine the relationship between maternal obesity and fetal umbilical arterial pH in a cohort of parturients that received a prophylactic phenylephrine infusion for management of spinal anesthesia induced hypotension during cesarean delivery.

Methods: This was a retrospective cohort study of cesarean deliveries at a single academic tertiary care institution between January 2012 and March 2019. All scheduled nonlaboring cesarean deliveries of singleton live neonate performed under spinal anesthesia between 37 and 41 weeks gestational age were included. The primary outcome was umbilical arterial pH. Multiple regression models were used to test the relationship between umbilical arterial pH, and maternal body mass index (BMI), race, dose of phenylephrine, baseline systolic blood pressure, maximum decrease in systolic blood pressure, induction of anesthesia to delivery time and uterine incision to delivery time.

Results: Seven hundred and sixty-one mother neonate pairs were included in the study. The univariate analysis showed a decrease in mean umbilical arterial pH with increasing maternal BMI (p = <.01). A multivariate regression model indicated that maximum decrease in systolic blood pressure, induction of anesthesia to delivery time, and uterine incision to delivery time accounted for 11% of the variance in the outcome, R² = 0.11. BMI was not a significant predictor of low umbilical arterial pH (p = .36). The significant predictors of low umbilical arterial pH in the model were maximum decrease in systolic blood pressure (p < .001), induction of anesthesia to delivery time (p = .04), and uterine incision to delivery time (p < .001).

Conclusions: Maternal BMI is not associated with lower umbilical arterial pH in women having scheduled cesarean delivery under spinal anesthesia. Severity of spinal anesthesia induced hypotension is greater with increasing BMI and may be responsible for the observed decrease in umbilical arterial pH.