Oxytocin versus carbetocin at elective Cesarean delivery in parturients with class III obesity: a double-blind randomized controlled noninferiority trial.

Purpose: Class III obesity (body mass index [BMI] ≥ 40 kg·m^-2) is associated with high rates of Cesarean deliveries and postpartum hemorrhage, with increased maternal and fetal morbidity. The doses of oxytocin and carbetocin are two to four times higher at Cesarean delivery in patients with class III obesity. We sought to investigate the efficacy of carbetocin 80 µg iv compared with oxytocin 1 IU iv (plus infusion) at elective Cesarean delivery in parturients with class III obesity. We hypothesized that, with equipotent dosing, carbetocin would be noninferior to oxytocin.

Methods: We conducted a randomized, double-blind, noninferiority study in nonlabouring, term parturients with BMI ≥ 40 kg·m^-2 undergoing elective Cesarean delivery under neuraxial anesthesia. Patients received either a 1-IU bolus of oxytocin iv followed by an infusion of 4.8 IU·hr^-1 or an 80-µg carbetocin bolus iv followed by a placebo infusion. Uterine tone was determined by palpation by the obstetrician at 3, 5, and 10 min, using a verbal numerical rating score of 0 (boggy) to 10 (firm). The primary outcome was uterine tone at 3 min. Secondary outcomes included uterine tone at 5 and 10 min, blood loss, additional uterotonics, and side effects.

Results: Forty-seven participants were included in the analysis. Median tone at 3 min was similar for oxytocin (8; 95% confidence interval [CI], 7 to 8) and carbetocin (8; 95% CI, 8 to 9) (P = 0.06), with no difference at 5 and 10 min. Blood loss, side effects, and the need for additional uterotonics were not significantly different between the study groups.

Conclusion: We conclude that carbetocin is noninferior to oxytocin at elective Cesarean delivery in parturients with class III obesity, with the advantage of single bolus dosing without infusion.

Study registration: ClinicalTrials.gov ( NCT04902729 ); first submitted 21 May 2021.