ABSTRACT
OBJECTIVE:
To examine associations between oxytocin dosing intensity and maternal outcomes—cesarean delivery and postpartum hemorrhage (PPH)—by body mass index (BMI).
METHODS:
This retrospective cohort study included singleton births from 2013 to 2022 at a large tertiary hospital among individuals receiving oxytocin for labor induction. Delivery BMI was classified as normal weight (18.5–24.9), overweight (25–29.9), class I–II obesity (30–39.9), and class III obesity (40 or above). Maximum oxytocin dose rate (milliunits per minute) was categorized into quartiles. Modified Poisson regression models, stratified by BMI, estimated risk ratios (RRs) for cesarean delivery and PPH, with adjustment for oxytocin exposure duration, insurance, maternal age, parity, gestational comorbidities, cervical status, gestational age, fetal sex, and birth weight.
RESULTS:
Among 20,215 deliveries, 16.9% were to individuals with normal weight, 43.1% to individuals with overweight, 35.1% to individuals with class I–II obesity, and 4.9% to individuals with class III obesity. Maximum oxytocin dose and exposure duration increased with BMI. Individuals in the highest oxytocin quartile (more than 18 milliunits/min) had elevated risk of cesarean delivery and PPH compared with individuals in the lowest two quartiles; associations were partially attenuated after adjustment. Risks associated with highest-quartile dosing were greater for those with normal weight (adjusted RR for cesarean delivery 1.8 [95% CI, 1.5–2.2]; PPH 3.0 [95% CI, 1.7–5.4]) than for those with obesity (cesarean delivery 1.2 [95% CI, 1.0–1.5], class III; PPH 1.6 [95% CI, 1.2–2.0], any class). Among individuals with overweight or obesity, third-quartile dosing was not associated with increased PPH risk.
CONCLUSION:
Elevated BMI was associated with greater oxytocin requirements, but risks associated with increased dosing were attenuated in individuals with higher BMI. Tailored dosing strategies may improve labor efficacy and maternal safety.