Patterns of recurrence of postpartum hemorrhage in a large population-based cohort

Although a history of postpartum hemorrhage (PPH) is a recognized risk factor for PPH in subsequent pregnancies, little is known about how the risk accumulates over multiple pregnancies, how recurrence varies by PPH subtype, and whether recurrence can be explained by chronic maternal conditions.

Risks of PPH were assessed according to a history of PPH, severity, and subtype (atony, retained placenta, or lacerations) in 538,332 primiparous women whose data were included in the Swedish Medical Birth Register from 1997-2009. The role of stable maternal risk factors was evaluated in regression models that predicted probability of recurrent PPH in second and third pregnancy.

Women with a history of PPH had a 3-fold increased risk of PPH in their second pregnancy compared with unaffected women (15.0% vs 5.0%, respectively). Adjustment for stable maternal risk factors did not attenuate this risk significantly (adjusted relative risk, 3.0; 95% confidence interval, 2.9-3.1). In a third pregnancy, the risk of PPH was 26.6% after 2 previously affected pregnancies, compared with 4.4% in women with no previous PPH. A history of a specific type of PPH predicted recurrence of PPH in the second pregnancy, not only of the same type but other causes as well.

PPH risk is highest among women with >1 previously affected delivery and in those with a previous severe PPH. Chronic conditions that are known to be risk factors for PPH do not explain the recurrence risks. The recurrence patterns across PPH subtypes may point to shared pathologic mechanisms underlying the varying PPH causes.