Risk factors for retained placenta in a first pregnancy—A clinical trial

Objective: To evaluate potential risk factors for retained placenta in a first pregnancy. Method: This retrospective case–control study included all primigravida with a singleton, live, vaginal birth at 24 weeks or later, at a tertiary hospital, 2014–2020. The cohort was divided into those with retained placenta versus controls. Retained placenta was defined as the need for manual extraction of the placenta or portions of it, immediately postpartum. Maternal and delivery characteristics, and obstetric and neonatal adverse outcomes, were compared between groups. Multivariable regression was performed to reveal potential risk factors for retained placenta. Results: Among 10 796 women, 435 (4.0%) had retained placenta and 10 361 (96.0%) controls did not. Multivariable logistic regression revealed nine potential risk factors for retained placenta: abruption (adjusted odds ratio [aOR] 3.58, 95% confidence interval [CI] 2.36–5.43), hypertensive disorders (aOR 1.74, 95% CI 1.17–2.57), prematurity (<37 weeks, aOR 1.63, 95% CI 1.13–2.35), maternal age older than 30 years (aOR 1.55, 95% CI 1.27–1.90), intrapartum fever (aOR 1.48, 95% CI 1.03–2.11), lateral placentation (aOR 1.39, 95% CI 1.01–1.91), oxytocin administration (aOR 1.39, 95% CI 1.11–1.74), diabetes mellitus (aOR 1.35, 95% CI 1.01–1.79), and female fetus (aOR 1.26, 95% CI 1.03–1.53). Conclusion: Retained placentas in first deliveries are associated with obstetric risk factors, some of which could be related to abnormal placentation.