Clinical risk factors for complete and partial placental retention ― a case-control study

We sought to investigate the incidence, maternal risk factors, and perinatal outcomes of women with complete and partial placental retention in a tertiary care teaching hospital in Southwestern Germany. We performed an unmatched case-control study with cases occurring between July 2000 and June 2007. Women were included into the study if they completed at least the 24th week of gestation and were diagnosed with placental retention requiring surgical intervention. We selected two controls per case and performed univariate and multivariate logistic regression analyses to identify risk factors for complete and partial placental retention. A total of 161 cases (2.02%) were identified out of 7978 deliveries. The 1-year prevalence of all types of placental retention continuously increased during the 6-year study period from 0.93% to 3.26%. A significant independent risk factor for all types of placental retention in the multivariate logistic regression model was a previous retention of the placenta [odds ratio (OR)=21.723, 95% confidence interval (CI) 6.07-77.7]. Independent protective factors against all types of placental retention were a non-anterior and non-posterior placenta location (OR=0.561, 95% CI 0.35-0.91), and a cesarean delivery with (OR=0.193, 95% CI 0.09-0.40) and without labor (OR=0.482, 95% CI 0.27-0.86). Women without partial placental retention delivered neonates with better 5-min APGAR scores (OR=0.78, 95% CI 0.65-0.95). A thorough medical history and a vigilant prepartum ultrasound help in identifying women at risk for placental retention.