A prospective cohort study of physical activity and time to pregnancy

Fertil Steril. 2012 May;97(5):1136-42.e1-4. doi: 10.1016/j.fertnstert.2012.02.025. Epub 2012 Mar 15.


Objective: To investigate the association between leisure-time physical activity (PA) and fecundability.

Design: Prospective cohort study.

Setting: Internet-based observational study of Danish women who were planning a pregnancy (2007-2009).

Patient(s): A total of 3,628 women aged 18-40 years at baseline.

Intervention(s): None.

Main outcome measure(s): 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).

Result(s): 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)).

Conclusion(s): 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.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adolescent
  • Adult
  • Body Mass Index
  • Confidence Intervals
  • Denmark / epidemiology
  • Female
  • Fertility*
  • Health Surveys
  • Humans
  • Internet
  • Leisure Activities*
  • Motor Activity*
  • Obesity / epidemiology
  • Obesity / physiopathology
  • Overweight / epidemiology
  • Overweight / physiopathology
  • Pregnancy
  • Pregnancy Rate
  • Proportional Hazards Models
  • Prospective Studies
  • Risk Assessment
  • Risk Factors
  • Surveys and Questionnaires
  • Thinness / epidemiology
  • Thinness / physiopathology
  • Time Factors
  • Young Adult