Novel risk factors associated with retained placenta after vaginal birth

Objective: To evaluate maternal and obstetric risk factors associated with retained placenta following singleton live vaginal births. Methods: We conducted a retrospective cohort study of women diagnosed with retained placenta after singleton live vaginal birth at or after 24 weeks of gestation, compared in a 1:2 ratio with women who had uncomplicated vaginal deliveries. The study and control groups were matched for maternal age, gestational age, and parity. Multivariate regression analysis assessed potential risk factors related to retained placenta. Results: In all, 15,260 women who delivered at our medical center(both vaginal and non-vaginal)between 2015 and 2022, 170 (1.1%) were diagnosed with retained placenta. Ninety-nine women (0.65%) who met the inclusion criteria were matched with 198 controls (1.3%). Multivariate logistic regression identified potential risk factors not previously described for retained placenta, including in vitro fertilization (OR 3.8, 95% CI 1.3–11.7, P = 00.018), large-for-gestational-age fetuses (OR 28.2, 95% CI 5.4–148.5, P = 00.029), and endometriosis (OR 8.2, 95% CI 0.92–20, P = 00.024). Additional risk factors included pre-eclampsia, labor induction, vacuum-assisted delivery, and prolonged second-stage labor. Conclusion: This study identifies critical risk factors for retained placenta, highlighting the importance of early identification to improve maternal and neonatal outcomes.