Risk Factors for Severe Postpartum Hemorrhage in Vaginal Delivery: A Retrospective Cohort Study

Abstract Objective: To investigate the risk factors for severe postpartum hemorrhage (SPPH) in vaginal delivery and explore targeted prediction and prevention strategies. Methods: A retrospective analysis of singleton pregnancies with vaginal deliveries after 28 weeks of gestation from January 1, 2021, to December 31, 2024, in the Peking Union Medical College Hospital was conducted. Women with multiple pregnancies, those with gestational age less than 28 weeks, and those giving birth through cesarean section were excluded. The primary outcome was SPPH, defined as blood loss of 1000 mL or more within 24 h of childbirth, or the presence of signs or symptoms of low blood volume requiring a transfusion of four or more units of red blood cells. Multivariate logistic regression was used to identify potential risk factors for SPPH. Results: A total of 6784 women were included in the study, with a SPPH rate of 1.3%. Low-lying placenta or placenta previa (adjusted odds ratio (a OR ) = 17.54, 95% confidence interval ( CI ): 5.01–61.41), placenta accreta spectrum (a OR = 5.25, 95% CI : 3.14–8.77), thrombocytopenia (a OR = 5.37, 95% CI : 1.12–25.78), precipitate labor (a OR = 3.35, 95% CI : 1.68–6.66), and episiotomy (a OR = 2.16, 95% CI : 1.20–3.90) were identified as independent risk factors for SPPH. Gestational age at delivery, use of assisted reproductive technology, neonatal birth weight, induction of labor or cervical ripening with prostaglandins, instrumental delivery, and duration of the second or third stage of labor showed statistical significance in the univariate analysis but not in the multivariate analysis. Conclusion: Placenta-related factors (placenta accreta spectrum, low-lying placenta, or placenta previa), thrombocytopenia, episiotomy, and precipitate labor were identified as factors potentially associated with SPPH in vaginal delivery. These findings should be interpreted with caution, given the limited number of events, and further validation through larger, multicenter studies is warranted.