Postpartum hemorrhage [PPH] can have serious consequences and is the leading cause of maternal mortality globally. Uterine contractility plays an important role in post-delivery uterine involution; impaired contractility can contribute to PPH. Should contractility be impaired among obese women, there would be implications for management. Therefore, the investigators sought to investigate whether obese women would also experience a need for more uterine agents during the management of an obstetric hemorrhage.

The American College of Obstetricians and Gynecologists (ACOG) updated their definition of postpartum hemorrhage (PPH) to be "blood loss greater than or equal to 1000 ml or blood loss accompanied by signs or symptoms of hypovolemia" .

Recent clinical and translational studies have suggested a decrease in uterine contractility among obese and morbidly obese women as a primary cause of obstetric hemorrhage.

In the United States, the prevalence of maternal obesity has been steadily rising, with more than half of pregnant women classified as overweight or obese. A panel of obstetric experts has speculated that the rising prevalence of maternal obesity in developed countries may explain the increase in postpartum hemorrhage incidence.

Uterotonic drugs are recommended to reduce blood loss and the risk of postpartum hemorrhage (PPH) after Cesarean delivery.

There are several prophylactic uterotonic agents available for use, including oxytocin, oxytocin/ergometrine, and carbetocin. Carbetocin is a synthetic analog of oxytocin which provides a longer duration of action than oxytocin (half-life 85-100 min versus 3-4 min).

The investigators aim to investigate the impact of carbetocin on uterine contractility in obese versus non-obese pregnant women undergoing elective cesarean delivery following carbetocin 100 mcg bolus IV administration as a prophylaxis of postpartum hemorrhage in a randomized controlled trial. The incestigators hypothesize that increased volume of distribution reduces the bioavailability of carbetocin and may be an explanation for reduced efficacy. Also the investigators will examine uterine tone as a surrogate marker for the bioavailability of carbetocin.

Inclusion Criteria:

• Healthy women with a singleton pregnancy undergoing a Cesarean delivery after at least 37 completed weeks of gestation under regional anesthesia.
• Aged (18-39) years and with signed informed consent.

Exclusion Criteria:

• Emergency Cesarean Section due to fetal distress.
• Maternal comorbidities such as severe cardiovascular disorders, kidney or liver disorders, coagulopathies, as well as epilepsy.
• Uterine malformation.
• Fetal malformation.
• Known hypersensitivity to carbetocin or oxytocin.
• Uterine overdistention (as in polyhydramnios, twins, and fetal macrosomia)
• Injury of uterine vessels during CS.