Objective: To identify risk factors associated with retained placenta after vaginal delivery.
Design: Case-control study.
Material and Method: Medical records of 234 pregnant women whose gestational age > 28 weeks were reviewed. Cases comprised of 78 women with retained placenta after vaginal delivery and controls comprised of 156 women with spontaneous placental delivery. Associated risk factors were examined. Chi-square test and logistic regression analysis were used for analysis of data.
Results: Cases were significantly older than controls (29.3 + 6.4 vs. 27.0 + 6.4 years respectively, p = 0.01). Cases were likely more significant than controls to have a previous history of uterine curettage (20.5% vs. 6.4% respectively, p = 0.001) and premature rupture of membranes (35.9% vs. 22.4% respectively, p = 0.029). Between the two groups, there were no differences in gestational age, parity, previous abortion, induction of labor, oxytocin, and pethidine usage. Logistic regression analysis showed that independent risk factors for retained placenta were age (adjusted OR 1.06, 95%CI 1.01-1.11), previous uterine curettage (adjusted OR 4.2, 95%CI 1.7-9.9), and PROM (adjusted OR 2.2, 95%CI 1.2-4.1).
Conclusion: Maternal age, previous uterine curettage, and PROM were independently associated with increased risk of retained placenta. The condition should be aware of among pregnant women with such risk factors.

Keywords: Retained placenta, Risk factors, Vaginal delivery