title: Occurrence of placental abruption in relatives.
abstract: OBJECTIVE
  The aim of this study was to assess the recurrence of placental abruption by severity, comparing the risk in a woman with that of recurrence in her sister and in the partner of her brother.
  
  
  METHODS
  Prospective observational study.
  
  
  METHODS
  General population.
  
  
  METHODS
  Population-based study based on records of pregnancies from the Medical Birth Registry of Norway; 377.902 sisters with 767 395 pregnancies, 168,142 families incorporating 2-10 sisters, and 346,385 brothers with 717,604 pregnancies in their partners were identified.
  
  
  METHODS
  Placental abruption with preterm birth, birthweight below 2500 g or perinatal death was defined as severe, other cases as mild. Because of the nested family data structure, multilevel multivariate regression was used.
  
  
  METHODS
  Placental abruption (severe and mild).
  
  
  RESULTS
  Adjusted odds ratios of recurrence of mild and severe abruption were 6.5 (1.7%) and 11.5 (3.8%), respectively, compared with risks of 0.2 and 0.3% in the total population. After a severe abruption, odds ratios in her sisters were 1.7-2.1, whereas mild abruption produced no increased recurrence in sisters. The estimated heritability between sisters of severe abruption was 16%. No excess rate of abruption was observed between sisters and brothers' partners, between brothers' partners, or from brothers' partners to sisters. The odds ratios for a third abruption after a second abruption and a second severe abruption were 38.7 (19%) and 50.1 (24%), respectively.
  
  
  CONCLUSIONS
  The recurrence risk of placental abruption in the same woman was higher after severe than mild abruption. Severe abruption was associated with a two-fold risk in sisters. Pregnancies following a second abruption should be considered very high risk.
authors.affiliation: Medical Birth Registry of Norway, Locus of Registry Based Epidemiology, Institute of Community Medicine and Primary Health Care, University of Bergen and Norwegian Institute of Public Health, Bergen, Norway. svein.rasmussen@mfr.uib.no
authors.forename: S
authors.initials: S
authors.lastname: Rasmussen
authors.forename: L M
authors.initials: LM
authors.lastname: Irgens
mesh_terms: D000037:Abruptio Placentae / Q000235:genetics*; D000328:Adult; D005260:Female; D006801:Humans; D015994:Incidence; D007231:Infant, Newborn; D007236:Infant, Small for Gestational Age; D015999:Multivariate Analysis; D007752:Obstetric Labor, Premature; D016017:Odds Ratio; D011247:Pregnancy; D011446:Prospective Studies; D012008:Recurrence; D012042:Registries; D017584:Reproductive History; D012307:Risk Factors; D035781:Siblings; D055815:Young Adult