In this trial, healthy term pregnant women undergoing elective cesarean delivery under spinal anesthesia will be recruited. The effective dose of carbetocin that will prevent postpartum uterine atony in 90% of the women (ED90) will be determined using a biased coin design up-down sequential allocation method. The determination of the carbetocin ED90 will help the anesthesiologist regarding the optimal dose of carbetocin to administer after elective cesarean delivery to prevent uterine atony.