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A Prospective Study of Physical Activity and Fecundability

Background: Physical activity (PA) may influence fecundability through alterations in endocrine function. The limited studies that have evaluated PA and fecundability in non-clinical populations have utilized internet-based recruitment, contain potential issues in measurement, and have yielded inconclusive results. Methods: We evaluated the association between PA and time-to-pregnancy in the Effects of Aspirin in Gestation and Reproduction trial, which included 1228 women attempting pregnancy ages 18–40 with prior pregnancy loss. PA was measured at baseline using the short form of the International Physical Activity Questionnaire to determine hours/week of activity (vigorous, moderate, and walking) and hours/day of sedentary (sitting) behavior. Pregnancy was assessed using urine hCG assays. Discrete time Cox models were used to estimate fecundability odds ratios (FORs) adjusted for marital status and parity, accounting for left truncation and right censoring. Results: We observed a positive association between fecundability and vigorous PA of ≥ 4 hrs/week vs. none (FOR= 1.55, 95% CI: 1.17, 2.07) adjusted for marital status and parity. In stratified multivariable models, this association was most pronounced among overweight/obese women reporting vigorous PA of ≥ 4 hrs/week compared to none (FOR=2.27, 1.41, 3.65); however, there was no significant effect modification. Fecundability was not associated with categorical measures of moderate PA, walking, or sitting. Conclusion: In this study, fecundability was positively associated with vigorous PA. Further study is necessary to clarify possible mechanisms to explain the relationship through which vigorous PA might affect time-to-pregnancy; however, such improvements in fecundability may be related to a reduction in ovulatory disorders.