Prophylactic Carbetocin Versus Oxytocin and Blood Loss After Vaginal Delivery: Agent Selection and Confounding by Indication in a Retrospective Cohort Study.

Abstract

Background and Objectives: Carbetocin is increasingly used for postpartum hemorrhage (PPH) prophylaxis, but its selection in routine practice may bias comparisons with oxytocin. This observational study examined the association between the agent received and blood loss after vaginal delivery. Materials and Methods: This retrospective cohort included 559 women delivering vaginally in 2022-2023 who received carbetocin 100 μg intravenously (n = 474) or oxytocin 10 IU by infusion (n = 85). Gravimetric blood loss was analyzed using linear (primary), robust and median (co-primary) regression, and propensity score methods. Results: Carbetocin recipients more often underwent induction (63.3% vs. 43.5%), vacuum extraction (26.8% vs. 15.3%), and epidural analgesia (76.2% vs. 29.4%). Blood loss was higher with carbetocin before adjustment (223.7 vs. 180.0 mL, p = 0.003) but not after adjustment (β 12.72 mL, 95% CI -50.19 to 75.64, p = 0.691; robust p = 0.479; median p = 0.354). Propensity score results conflicted: inverse probability weighting showed higher blood loss with carbetocin (47.84 mL, p = 0.002), whereas matching and trimmed weighting did not. PPH occurred in 2.7% vs. 0% (p = 0.234). Conclusions: Carbetocin was preferentially used in higher-risk labors, indicating confounding by indication. Adjusted blood loss did not differ significantly, although a modest increase could not be excluded. The study was severely underpowered for PPH.