title: A prospective cohort study of physical activity and time to pregnancy.
abstract: OBJECTIVE
  To investigate the association between leisure-time physical activity (PA) and fecundability.
  
  
  METHODS
  Prospective cohort study.
  
  
  METHODS
  Internet-based observational study of Danish women who were planning a pregnancy (2007-2009).
  
  
  METHODS
  A total of 3,628 women aged 18-40 years at baseline.
  
  
  METHODS
  None.
  
  
  METHODS
  Time to pregnancy (TTP). Fecundability ratios (FRs) and 95% confidence intervals (CIs) were derived from discrete-time Cox models, with adjustment for potential confounders, such as body mass index (BMI).
  
  
  RESULTS
  We observed an inverse monotonic association between vigorous PA and fecundability (≥ 5 h/wk vs. none: FR 0.68, 95% CI 0.54-0.85) and a weak positive association between moderate PA and fecundability (≥ 5 vs. <1 h/wk: FR 1.18, 95% CI 0.98-1.43) after mutual adjustment for both PA types. Inverse associations between high vigorous PA and fecundability were observed within subgroups of age, parity status, and cycle regularity, but not among overweight or obese women (BMI ≥ 25 kg/m(2)).
  
  
  CONCLUSIONS
  There was evidence for a dose-response relationship between increasing vigorous PA and delayed TTP in all subgroups of women with the exception of overweight and obese women. Moderate PA was associated with a small increase in fecundability regardless of BMI. These findings indicate that PA of any type might improve fertility among overweight and obese women, a subgroup at higher risk of infertility. Lean women who substitute vigorous PA with moderate PA may also improve their fertility.
authors.affiliation: Department of Epidemiology, Boston University School of Public Health, Boston, Massachusetts, USA. lwise@bu.edu
authors.forename: Lauren A
authors.initials: LA
authors.lastname: Wise
authors.forename: Kenneth J
authors.initials: KJ
authors.lastname: Rothman
authors.forename: Ellen M
authors.initials: EM
authors.lastname: Mikkelsen
authors.forename: Henrik Toft
authors.initials: HT
authors.lastname: Sørensen
authors.forename: Anders H
authors.initials: AH
authors.lastname: Riis
authors.forename: Elizabeth E
authors.initials: EE
authors.lastname: Hatch
mesh_terms: D000293:Adolescent; D000328:Adult; D015992:Body Mass Index; D016001:Confidence Intervals; D003718:Denmark / Q000453:epidemiology; D005260:Female; D005298:Fertility; D006306:Health Surveys; D006801:Humans; D020407:Internet; D007899:Leisure Activities; D009043:Motor Activity; D009765:Obesity / Q000453:epidemiology / Q000503:physiopathology; D050177:Overweight / Q000453:epidemiology / Q000503:physiopathology; D011247:Pregnancy; D018873:Pregnancy Rate; D016016:Proportional Hazards Models; D011446:Prospective Studies; D018570:Risk Assessment; D012307:Risk Factors; D011795:Surveys and Questionnaires; D013851:Thinness / Q000453:epidemiology / Q000503:physiopathology; D013997:Time Factors; D055815:Young Adult