Mediating Effects of Cardiometabolic Risk Factors on the Association Between Maternal Race-Ethnicity and Cesarean Delivery Among Low-Risk Women.

While racial-ethnic disparities in cesarean delivery rates among nulliparous women delivering a term singleton in the vertex position (NTSV) exist, it remains unclear the extent to which potentially modifiable maternal cardiometabolic risk factors (obesity, maternal hyperglycemia and hypertensive disorders) underlie these disparities. We examined race-ethnicity and risk of NTSV cesarean deliveries and whether the associations were mediated by maternal cardiometabolic risk factors. A cohort study of 62,048 NTSV deliveries in Kaiser Permanente Northern California. The outcome was cesarean delivery. Black, Asian, and Hispanic women were at increased risk of having a NTSV cesarean delivery compared with White women (relative risks and 95% confidence intervals: 1.37 [1.28-1.45]; 1.11 [1.07-1.16]; 1.12 [1.07-1.16], respectively), independent of established risk factors and prenatal care utilization. The extent to which cardiometabolic risk factors mediated the associations between race-ethnicity (each group vs. White, in separate analyses) and NTSV cesarean delivery varied by race-ethnicity. Maternal overweight/obesity (body mass index ≥25.0) mediated the association between Black and Hispanic race-ethnicity and NTSV cesarean delivery (21.1% [15.8-26.4] and 24.7% [14.6-34.8, respectively), but not for Asian race. Maternal hyperglycemia (gestational diabetes mellitus or preexisting diabetes) mediated the association between Asian and Hispanic race and NTSV cesarean delivery (18.5% [9.8-27.2] and 9.8% [5.0-14.7], respectively), but not for Black race. Hypertensive disorders mediated 3.2% (0.70-5.8) of the association between Black race and cesarean delivery, but not for other race-ethnicities. Black, Asian, and Hispanic women are at increased risk for NTSV cesarean deliveries. Maternal cardiometabolic risk factors only partially mediate the associations between race-ethnicity and NSTV cesarean deliveries.