PostPartum hemorrhage (PPH) is a major cause of maternal death worldwide. Oxytocin is the most commonly used uterotonic drug to prevent and treat PPH in North America. However oxytocin has a very short duration of action, requiring a continuous infusion to achieve sustained uterotonic activity. Moreover large doses are associated with adverse effects like hypotension, nausea, vomiting, dysrhythmias and ST changes. The Society of Obstetricians and Gynecologists of Canada (SOGC) has recommended a single dose of 100 mcg of carbetocin at elective cesarean delivery to promote uterine contraction. In three studies recently performed at Mount Sinai Hospital, the investigators have found no difference in uterine contractility between the doses of 20- 120 mcg carbetocin and that the ED90 is 14.8 mcg. Thus a larger trial comparing the minimum effective dose determined in the previous three trials with the standard 100 mcg dose is necessary to confirm these findings.

The current oxytocin regimen requires the administration of a continuous infusion to achieve sustained uterotonic activity, which can be associated with a number of side effects and unpredictable efficacy. Carbetocin in a single 100 mcg dose has apparently greater efficacy, with a similar side effect profile to that of oxytocin. In addition, some studies have also shown that there is less blood loss and less requirement for additional uterotonic drugs when carbetocin is administered. Studies conducted by the investigators group at Mount Sinai have shown similar efficacy between the doses ranging from 20 to 100 mcg of carbetocin. In the investigators study, the investigators are going to compare those two doses of carbetocin to determine that 20 mcg is not inferior to 100 mcg to produce adequate uterine tone in elective cesarean delivery. This study will be a randomized, double - blind, non inferiority study.

Inclusion Criteria:

• Elective cesarean delivery under spinal anesthesia.
• Written informed consent to participate in this study.
• Term pregnancy

Exclusion Criteria:

• Refusal to give written informed consent.
• Allergy or hypersensitivity to carbetocin or oxytocin.
• Conditions that predispose to uterine atony and postpartum hemorrhage, such as placenta previa, multiple gestation, preeclampsia, eclampsia, macrosomia, polyhydramnios, uterine fibroids, previous history of uterine atony and postpartum bleeding, or bleeding diathesis.
• Hepatic, renal, and vascular disease.