title: Hypertensive diseases in pregnancy and breast cancer risk.
abstract: BACKGROUND
  Hypertensive diseases in pregnancy may be associated with a reduced risk of breast cancer. Most previous studies are small and have shown conflicting results.
  
  
  METHODS
  In a cohort of 919 712 women who gave their first birth between 1967 and 2008, with linkage of information from two national registries, we assessed whether women with pregnancy hypertensive diseases are at reduced breast cancer risk. We used Cox regression to estimate hazard ratios (HRs) with 95% confidence intervals (CI).
  
  
  RESULTS
  Compared with women with a normotensive first pregnancy, women with hypertension or preeclampsia in their first pregnancy had a reduced breast cancer risk (HR 0.83, 95% CI 0.77, 0.90). A reduced risk was consistently observed for hypertensive disease in any pregnancy, for recurrent hypertensive disease in pregnancy, and before and after 50 years of age at breast cancer diagnosis. The association was strongest for women with hypertension in pregnancy, who delivered at term/post-term (HR 0.81, 95% CI 0.75, 0.88) or had a child of average birth weight (HR 0.77, 95% CI 0.69, 0.85).
  
  
  CONCLUSIONS
  Women with pregnancy hypertensive diseases are at reduced breast cancer risk. Whether this association can be attributed to pregnancy-specific events or to underlying biological traits remains unclear.
authors.affiliation: Department of Public Health and Community Medicine, Faculty of Medicine, Norwegian University of Science and Technology, NTNU, Postbox 8905, MTFS, Trondheim N-7491, Norway. signe.opdahl@ntnu.no
authors.forename: S
authors.initials: S
authors.lastname: Opdahl
authors.forename: P R
authors.initials: PR
authors.lastname: Romundstad
authors.forename: M D K
authors.initials: MD
authors.lastname: Alsaker
authors.forename: L J
authors.initials: LJ
authors.lastname: Vatten
mesh_terms: D000328:Adult; D001722:Birth Order; D001943:Breast Neoplasms / Q000453:epidemiology*; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D006973:Hypertension / Q000453:epidemiology*; D008875:Middle Aged; D009664:Norway / Q000453:epidemiology; D011225:Pre-Eclampsia / Q000453:epidemiology*; D011247:Pregnancy; D012306:Risk; D055815:Young Adult