Retained placenta is associated with pre-eclampsia, stillbirth, giving birth to a small-for-gestational-age infant, and spontaneous preterm birth: a national register-based study.

OBJECTIVE: To evaluate whether defective placentation disorders, i.e. pre-eclampsia, stillbirth, small for gestational age (SGA), and spontaneous preterm birth, are associated with risk of retained placenta.

DESIGN: Population-based cohort study.

SETTING: Sweden.

POPULATION: Primiparous women in Sweden with singleton vaginal deliveries between 1997 and 2009 at 32-41 weeks of gestation (n = 386,607), without placental abruption or infants with congenital malformations.

METHODS: Risks were calculated as odds ratios (ORs) by unconditional logistic regression with 95% confidence intervals (95% CIs) after adjustments for maternal, delivery, and infant characteristics.

MAIN OUTCOME MEASURE: Retained placenta, defined by the presence of both a diagnostic code (of retained placenta) and a procedure code (for the manual removal of the placenta).

RESULTS: The overall rate of retained placenta was 2.17%. The risk of retained placenta was increased for women with pre-eclampsia (adjusted OR, aOR, 1.37, 95% CI 1.21-1.54), stillbirth (aOR 1.71, 95% CI 1.28-2.29), SGA birth (aOR 1.47, 95% CI 1.28-1.70), and spontaneous preterm birth (32-34 weeks of gestation, aOR 2.35, 95% CI 1.97-2.81; 35-36 weeks of gestation, aOR 1.55, 95% CI 1.37-1.75). The risk was further increased for women with preterm pre-eclampsia (aOR 1.69, 95% CI 1.25-2.28) and preterm SGA birth (aOR 2.19, 95% CI 1.42-3.38). There was no association between preterm stillbirth (aOR 1.10, 95% CI 0.63-1.92) and retained placenta, but the exposed group comprised only 15 cases.

CONCLUSIONS: Defective placentation disorders are associated with an increased risk of retained placenta. Whether these relationships indicate a common pathophysiology remains to be investigated.