title: Genetic contribution to postpartum haemorrhage in Swedish population: cohort study of 466,686 births.
abstract: OBJECTIVE
  To investigate the familial clustering of postpartum haemorrhage in the Swedish population, and to quantify the relative contributions of genetic and environmental effects.
  
  
  METHODS
  Register based cohort study.
  
  
  METHODS
  Swedish population (multi-generation and medical birth registers).
  
  
  METHODS
  Postpartum haemorrhage, defined as >1000 mL estimated blood loss.
  
  
  METHODS
  The first two live births to individuals in Sweden in 1997-2009 contributed to clusters representing intact couples (n = 366,350 births), mothers with separate partners (n = 53,292), fathers with separate partners (n = 47,054), sister pairs (n = 97,228), brother pairs (n = 91,168), and mixed sibling pairs (n = 177,944).
  
  
  METHODS
  Familial clustering was quantified through cluster specific tetrachoric correlation coefficients, and the influence of potential sharing of known risk factors was evaluated with alternating logistic regression. Relative contributions of genetic and environmental effects to the variation in liability for postpartum haemorrhage were quantified with generalised linear mixed models.
  
  
  RESULTS
  The overall prevalence of postpartum haemorrhage after vaginal deliveries in our sample was 4.6%. Among vaginal deliveries, 18% (95% confidence interval 9% to 26%) of the variation in postpartum haemorrhage liability was attributed to maternal genetic factors, 10% (1% to 19%) to unique maternal environment, and 11% (0% to 26%) to fetal genetic effects. Adjustment for known risk factors only partially explained estimates of familial clustering, suggesting that the observed shared genetic and environmental effects operate in part through pathways independent of known risk factors. There were similar patterns of familial clustering for both of the main subtypes examined (atony and retained placenta), though strongest for haemorrhage after retained placenta.
  
  
  CONCLUSIONS
  There is a maternal genetic predisposition to postpartum haemorrhage, but more than half of the total variation in liability is attributable to factors that are not shared in families.
authors.affiliation: Department of Epidemiology, Harvard School of Public Health, Boston, MA 02115, USA Department of Medical Epidemiology and Biostatistics, Karolinska Institutet, PO-box 281, S-171 77 Stockholm, Sweden oberg@hsph.harvard.edu.
authors.forename: Anna Sara
authors.initials: AS
authors.lastname: Oberg
authors.affiliation: Department of Epidemiology, Harvard School of Public Health, Boston, MA 02115, USA.
authors.forename: Sonia
authors.initials: S
authors.lastname: Hernandéz-Diaź
authors.affiliation: Clinical Epidemiology Unit, Department of Medicine, Karolinska University Hospital, Eugeniahemmet T2, S-171 76 Stockholm, Sweden.
authors.forename: Thomas
authors.initials: T
authors.lastname: Frisell
authors.affiliation: Department of Obstetrics and Gynecology, Massachusetts General Hospital, Harvard Medical School, Boston, MA 02114, USA.
authors.forename: Michael F
authors.initials: MF
authors.lastname: Greene
authors.affiliation: Department of Medical Epidemiology and Biostatistics, Karolinska Institutet, PO-box 281, S-171 77 Stockholm, Sweden Astrid Lindgren Children's Hospital, Lung and Allergy Unit, Karolinska University Hospital, S-171 76 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 Harvard Medical School, Boston, MA 02115, USA Department of Anesthesia, Critical Care, and Pain Medicine, Massachusetts General Hospital and Harvard Medical School, Boston, MA 02114, USA.
authors.forename: Brian T
authors.initials: BT
authors.lastname: Bateman
mesh_terms: D000328:Adult; D015331:Cohort Studies; D005260:Female; D006801:Humans; D016014:Linear Models; D016015:Logistic Models; D018457:Placenta, Retained / Q000453:epidemiology / Q000235:genetics*; D006473:Postpartum Hemorrhage / Q000453:epidemiology / Q000235:genetics*; D011247:Pregnancy; D015995:Prevalence; D013548:Sweden / Q000453:epidemiology; D014593:Uterine Inertia / Q000453:epidemiology / Q000235:genetics*; D055815:Young Adult