Risk of retained placenta in women previously delivered by caesarean section : a population-based cohort study.

• OBJECTIVE: To evaluate whether women with a caesarean section at their first delivery have an increased risk of retained placenta at their second delivery.DESIGN: Population-based cohort study.SETTING: Sweden.POPULATION: All women with their first and second singleton deliveries in Sweden during the years 1994-2006 (n = 258 608). Women with caesarean section or placental abruption in their second pregnancy were not included in the study population.METHODS: The risk of retained placenta at second delivery was estimated for women with a first delivery by caesarean section (n = 19 458), using women with a first vaginal delivery as reference (n = 239 150). Risks were calculated as odds ratios by unconditional logistic regression analysis with 95% confidence intervals (95%) after adjustments for maternal, delivery, and infant characteristics.MAIN OUTCOME MEASURES: Retained placenta with normal (≤1000 ml) and heavy (>1000 ml) bleeding.RESULTS: The overall rate of retained placenta was 2.07%. In women with a previous caesarean section and in women with previous vaginal delivery, the corresponding rates were 3.44% and 1.96%, respectively. Compared with women with a previous vaginal delivery, women with a previous caesarean section had an increased risk of retained placenta (adjusted OR 1.45; 95% CI 1.32-1.59), and the association was more pronounced for retained placenta with heavy bleeding (adjusted OR 1.61; 95% CI 1.44-1.79).CONCLUSIONS: Our report shows an increased risk for retained placenta in women previously delivered by caesarean section, a finding that should be considered in discussions of mode of delivery.

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