title: ABO blood groups and risk of venous thromboembolism during pregnancy and the puerperium. A population-based, nested case-control study.
abstract: OBJECTIVE
  To examine possible associations of ABO blood types with the risk of venous thromboembolism (VTE) in pregnancy and the puerperium.
  
  
  METHODS
  We conducted a nested case-control study within a cohort of 71,729 women who gave birth to 126,783 children in the North Jutland County, Denmark, from 1980 to 2001. We identified 129 cases with VTE in pregnancy (n = 61) or the puerperium (n = 68), and 258 controls with no VTE. We collected information on ABO blood groups and possible maternal confounding factors and estimated the relative risk [odds ratio (OR)].
  
  
  RESULTS
  Women with an A or AB blood group had elevated risk estimates of VTE in pregnancy or the puerperium compared with women with a O blood group [adjusted ORs 2.4, 95% confidence interval (CI) 1.3, 4.3, and 2.0, 95% CI 0.7, 5.8, respectively]. No increased risk estimate was found for group B (adjusted OR 1.2, 95% CI 0.5, 3.0). The increased risk estimates of VTE for blood groups A and AB appeared present in both pregnancy (adjusted ORs of 3.9, 95% CI 1.5, 9.7, and 2.2, 95% CI 0.4, 12.5) and in the puerperium (adjusted ORs of 2.4, 95% CI 1.0, 4.9 and 2.7, 95% CI 0.8, 9.3). Furthermore, blood groups A and AB appeared to be associated with increased risk estimates for both DVT and pulmonary embolism.
  
  
  CONCLUSIONS
  Keeping the modest statistical precision of our study in mind, blood groups A and AB may be associated with increased risk estimates for VTE in pregnancy and the puerperium.
authors.affiliation: Department of Clinical Biochemistry and Genetics, Odense University Hospital, Sdr. Boulevard 29, DK-5000 Odense, Denmark. tblarsen@dadlnet.dk
authors.forename: T B
authors.initials: TB
authors.lastname: Larsen
authors.forename: S P
authors.initials: SP
authors.lastname: Johnsen
authors.forename: M
authors.initials: M
authors.lastname: Gislum
authors.forename: C A I
authors.initials: CA
authors.lastname: Møller
authors.forename: H
authors.initials: H
authors.lastname: Larsen
authors.forename: H T
authors.initials: HT
authors.lastname: Sørensen
mesh_terms: D000017:ABO Blood-Group System / Q000502:physiology*; D000328:Adult; D016022:Case-Control Studies; D005260:Female; D006801:Humans; D016017:Odds Ratio; D049590:Postpartum Period / Q000097:blood*; D011237:Predictive Value of Tests; D011247:Pregnancy; D011249:Pregnancy Complications, Cardiovascular / Q000097:blood / Q000453:epidemiology / Q000209:etiology*; D018570:Risk Assessment; D013923:Thromboembolism / Q000097:blood / Q000453:epidemiology / Q000209:etiology; D020246:Venous Thrombosis / Q000097:blood / Q000453:epidemiology / Q000209:etiology*
chemical_list: D000017:ABO Blood-Group System