title: Body mass index at age 20 and subsequent childbearing: the Adventist Health Study-2.
abstract: BACKGROUND
  Some epidemiological, clinical, and laboratory studies suggest that underweight and obesity impact fertility.
  
  
  METHODS
  This is cross-sectional study of 33,159 North American Adventist women, who were nulliparous at age 20 years and who, as a group, have a healthy lifestyle. Logistic regression analysis was used to assess how body mass index (BMI, kg/m(2)) at age 20 was related to never becoming pregnant, never giving birth to a living child, or not giving birth to a second or third child.
  
  
  RESULTS
  A total of 4954 (15%) of the women reported never becoming pregnant (nulligravidity) and 7461 (23%) women remained nulliparous. Underweight (BMI<18.5 kg/m(2)) at age 20 was associated with approximately 13% increased risk of nulligravidity or nulliparity. Women with BMI≥32.5 kg/m(2) when aged 20 had 2.5 (95% CI: 2.0, 3.1) times increased odds of nulliparity compared to women with BMI 20-24.9 kg/m(2). Increased risk was found for all groups of overweight women (BMI≥25 kg/m(2)). However, if the women gave birth to one live child after age 20, BMI≥32.5 kg/m(2) at age 20 had less impact (OR 1.6 [95% CI: 1.2, 2.2]) on the likelihood of not delivering a second child. In women who delivered two living children, obesity at age 20 had no bearing on the odds of having a third child.
  
  
  CONCLUSIONS
  Obesity and, to a lesser extent, underweight at age 20 increases the nulliparity rate. The results underscore the importance of a healthy weight in young women.
authors.affiliation: Department of Community Medicine, University of Tromsø, Tromsø, N-9037 Tromsø, Norway. bjarne.jacobsen@uit.no
authors.forename: Bjarne K
authors.initials: BK
authors.lastname: Jacobsen
authors.forename: Synnøve F
authors.initials: SF
authors.lastname: Knutsen
authors.forename: Keiji
authors.initials: K
authors.lastname: Oda
authors.forename: Gary E
authors.initials: GE
authors.lastname: Fraser
mesh_terms: D000367:Age Factors; D015992:Body Mass Index; D003430:Cross-Sectional Studies; D005260:Female; D005298:Fertility / Q000502:physiology*; D006306:Health Surveys; D006801:Humans; D008019:Life Style; D016015:Logistic Models; D009765:Obesity / Q000503:physiopathology*; D010298:Parity; D011247:Pregnancy; D011256:Pregnancy Outcome; D033303:Protestantism; D012307:Risk Factors; D013851:Thinness / Q000503:physiopathology*; D014481:United States / Q000453:epidemiology; D055815:Young Adult