title: Breast cancer risk after childbirth in young women with family history (Denmark).
abstract: OBJECTIVE
  The increased risk of breast cancer in women with family history of breast cancer (FHBC) might be reduced by early childbirths. However, childbirth induces a transient increase in risk in the first 5-10 years, which coincides with the relatively increased risk of family cases at a young age. The objective was to investigate this short-term change in risk according to FHBC.
  
  
  METHODS
  We used a population-based cohort of 1.5 million Danish women. Between 1968 and 1990, 2770 incident cases of breast cancer below 40 years of age were identified in the Danish Cancer Register, of whom 276 (10%) had a FHBC.
  
  
  RESULTS
  The first 5 years after a birth the short-term increase in risk was 30% (3-64%) larger in women with FHBC than without FHBC. After the first 5 years we observed no difference in the effect of a birth between women with and without FHBC.
  
  
  CONCLUSIONS
  The adverse short-term effect of childbirthis stronger in women with FHBC.
authors.affiliation: Department of Epidemiology Research, Danish Epidemiology Science Center, Statens Serum Institut, Copenhagen.
authors.forename: Jan
authors.initials: J
authors.lastname: Wohlfahrt
authors.forename: Jørgen H
authors.initials: JH
authors.lastname: Olsen
authors.forename: Mads
authors.initials: M
authors.lastname: Melby
mesh_terms: D000293:Adolescent; D000328:Adult; D017668:Age of Onset; D001943:Breast Neoplasms / Q000453:epidemiology / Q000209:etiology* / Q000235:genetics*; D002648:Child; D015331:Cohort Studies; D003718:Denmark / Q000453:epidemiology; D005192:Family Health; D005260:Female; D006801:Humans; D008487:Medical History Taking; D010298:Parity; D049590:Postpartum Period; D011247:Pregnancy; D012307:Risk Factors; D013997:Time Factors