(Anesth Analg. 2015;121:159–164)

Postpartum hemorrhage is a leading cause of maternal mortality and is most frequently caused by uterine atony. Prophylactic administration of oxytocin during the third stage of labor has been shown to lower both uterine atony and the risk of postpartum hemorrhage. However, laboring patients who have already been administered oxytocin and subsequently undergo cesarean delivery due to labor dystocia will likely require a greater than normal amount of oxytocin to achieve adequate uterine tone because of desensitization. The purpose of this study was to determine the effective dose (ED₉₀) of oxytocin infusion for these laboring patients compared with the effective dose for nonlaboring patients who undergo elective cesarean delivery.