The inherited risk of retained placenta: a population based cohort study

Abstract

Objective: To investigate whether retained placenta in the first generation is associated with an increased risk of retained placenta in the second generation. Design: Population-based cohort study. Setting: Sweden. Population: Using linked generational data from the Swedish Medical Birth Register 1973–2012, we identified 494 000 second-generation births with information on the birth of the mother (first-generation index birth). For 292 897 of these births there was information also on the birth of the father. Methods: Risk of retained placenta in the second generation was calculated as adjusted odds ratios (aOR) by unconditional logistic regression with 95% confidence intervals (95% CI) according to whether retained placenta occurred in a first generation birth or not. Main outcome: Retained placenta in the second generation. Results: The risk of retained placenta in a second-generation birth was increased if retained placenta had occurred at the mother's own birth (aOR 1.66, 95% CI 1.52–1.82), at the birth of one of her siblings (aOR 1.58, 95% CI 1.43–1.76) or both (aOR 2.75, 95% CI 2.18–3.46). The risk was slightly increased if retained placenta had occurred at the birth of the father (aOR 1.23, 95% CI 1.07–1.41). For preterm births in both generations, the risk of retained placenta in the second generation was increased six-fold if retained placenta had occurred at the mother's birth (OR 6.55, 95% CI 2.68–16.02). Conclusion: There is an intergenerational recurrence of retained placenta on the maternal and most likely also on the paternal side. The recurrence risk seems strongest in preterm pregnancies. Tweetable abstract: A population-based cohort study suggests that there is an intergenerational recurrence of retained placenta.