High-dose oxytocin: 20- versus 40-minute dosage interval

Objective: To determine whether an increase in the oxytocin dosing interval would decrease the incidence of uterine hyperstimulation. Methods: This study included 1801 consecutive pregnancies receiving high-dose oxytocin. Oxytocin was used for labor augmentation in 1167 and induction in 634 women. Twenty- and 40-minute dosage intervals were compared. The study period was based on an 80% likelihood of detecting 5 and 10% differences in the cesarean and hyperstimulation rates, respectively. Statistics were analyzed with χ², Fisher, and Wilcoxon rank-sum tests where appropriate. Multivariate logistic regression and analysis of covariance were used to control for confounding demographic variables. Results: Comparison of the 20- and 40-minute regimens for labor induction yielded no differences in the rates of cesarean delivery for dystocia (16 versus 19%) or fetal distress (5 versus 6%). The 20-minute regimen for augmentation was associated with a significant reduction in cesarean for dystocia (8 versus 12%; P =.05). The incidence of uterine hyperstimulation was greater with the 20-minute than the 40-minute regimen for induction (40 versus 31%; P =.02), but not for augmentation (31 versus 28%). Neonatal outcomes were unaffected by the dosage interval for both augmentation and induction. Conclusion: A 40-minute dosing interval for high-dose oxytocin offers no clear advantage over a 20-minute interval. Both regimens were safe and efficient, with no differences in perinatal outcome. The 20-minute interval was associated with fewer cesareans for dystocia when used for labor augmentation, whereas the 40-minute interval resulted in less hyperstimulation when used for labor induction.