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.