High-Dose Compared With Standard-Dose Oxytocin Regimens to Augment Labor in Nulliparous Women A Randomized Controlled Trial

OBJECTIVE: To evaluate whether a high-dose oxytocin regimen reduces the risk for primary cesarean birth and other obstetric morbidities when compared with standard dosing. METHODS: In a double-blind randomized clinical trial of nulliparous women at or beyond 36 weeks of gestation who were undergoing augmentation of labor, participants were assigned to high-dose (initial and incremental rates of 6 milliunits/min) or standard-dose (initial and incremental rates of 2 milliunits/min) oxytocin regimens. The primary outcome was cesarean birth. Prespecified secondary outcomes included labor duration, clinical chorioamnionitis, endometritis, postpartum hemorrhage, Apgar score 3 or less at 5 minutes, umbilical artery acidemia, neonatal intensive care unit admission, perinatal death, and a severe perinatal morbidity composite. A sample size of 501 per group (n=1,002) was planned to detect a 6.6% absolute reduction in rate of the primary outcome, from 20% in the standard-dose group to 13.4% in the high-dose group with 80% power. RESULTS: From September 2015 to September 2020, 1,003 participants were randomized-502 assigned to high-dose and 501 assigned to standard dosing. The majority of participants were of White race, were married or living as married, and had commercial insurance. Baseline characteristics between groups were similar. The primary outcome occurred in 14.5% of those receiving high-dose compared with 14.4% of those receiving standard-dose oxytocin (relative risk, 1.01; 95% CI 0.75-1.37). The high-dose group had a significantly shorter mean labor duration (9.1 vs 10.5 hours; P<.001), and a significantly lower chorioamnionitis incidence (10.4% vs 15.6%; relative risk, 0.67; 95% CI 0.48-0.92) compared with standard dosing. Umbilical artery acidemia was significantly less frequent in the high-dose group in complete case analysis, but this finding did not persist after multiple imputation (relative risk, 0.55; 95% CI 0.29-1.04). There were no significant differences in other secondary outcomes. CONCLUSION: Among nulliparous participants who were undergoing augmentation of labor, a high-dose oxytocin regimen, compared with standard dosing, did not affect the cesarean birth risk but significantly reduced labor duration and clinical chorioamnionitis frequency without adverse effects on perinatal outcomes.