title: Patterns of recurrence of postpartum hemorrhage in a large population-based cohort.
abstract: OBJECTIVE
  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.
  
  
  METHODS
  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.
  
  
  RESULTS
  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.
  
  
  CONCLUSIONS
  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.
authors.affiliation: Department of Epidemiology, Harvard School of Public Health, Boston, MA; Department of Medical Epidemiology and Biostatistics, Karolinska Institutet, Stockholm, Sweden.
authors.forename: Anna Sara
authors.initials: AS
authors.lastname: Oberg
authors.affiliation: Department of Epidemiology, Harvard School of Public Health, Boston, MA.
authors.forename: Sonia
authors.initials: S
authors.lastname: Hernandez-Diaz
authors.affiliation: Department of Epidemiology, Harvard School of Public Health, Boston, MA.
authors.forename: Kristin
authors.initials: K
authors.lastname: Palmsten
authors.affiliation: Department of Medical Epidemiology and Biostatistics, Karolinska Institutet, Stockholm, Sweden; Lung and Allergy Unit, Astrid Lindgren Children's Hospital, Stockholm, Sweden.
authors.forename: Catarina
authors.initials: C
authors.lastname: Almqvist
authors.affiliation: Division of Pharmacoepidemiology and Pharmacoeconomics, Department of Medicine, Brigham and Women's Hospital, and the Department of Anesthesiology, Critical Care, and Pain Medicine, Massachusetts General Hospital, Harvard Medical School, Boston, MA.
authors.forename: Brian T
authors.initials: BT
authors.lastname: Bateman
mesh_terms: D000328:Adult; D015331:Cohort Studies; D005260:Female; D006801:Humans; D018457:Placenta, Retained / Q000453:epidemiology*; D006473:Postpartum Hemorrhage / Q000453:epidemiology*; D011247:Pregnancy; D011272:Pregnancy, Multiple; D011446:Prospective Studies; D012008:Recurrence; D012306:Risk
keywords: epidemiology; postpartum hemorrhage; recurrence; retained placenta; uterine atony