Body mass index physical activity and fecundability in a North American preconception cohort study

Craig J. McKinnon, M.P.H., Elizabeth E. Hatch, Ph.D., Kenneth J. Rothman, Dr.P.H., Ellen M. Mikkelsen, Ph.D., Amelia K. Wesselink, M.P.H., Kristen A. Hahn, Ph.D., Lauren A. Wise, Sc.D.


To evaluate the association between adiposity, physical activity (PA), and fecundability.

Prospective cohort study.

Not applicable.

A total of 2,062 female pregnancy planners from the United States and Canada who were enrolled during the preconception period.


Main Outcome Measure(s):
Self-reported pregnancy. Fecundability ratios (FRs) and 95% confidence intervals (CIs) were estimated using proportional probabilities models that adjusted for potential confounders.

Relative to body mass index (BMI) 18.5–24 kg/m2, FRs for BMI <18.5, 25–29, 30–34, 35–39, 40–44, and ≥45 kg/m2 were 1.05 (95% CI 0.76–1.46), 1.01 (95% CI 0.89–1.15), 0.98 (95% CI 0.82–1.18), 0.78 (95% CI 0.60–1.02), 0.61 (95% CI 0.42–0.88), and 0.42 (95% CI 0.23–0.76), respectively. Reduced fecundability was observed among women with the largest waist-to-hip ratios (≥0.85 vs. <0.75; FR = 0.87, 95% CI 0.74–1.01) and waist circumferences (≥36 vs. <26 inches; FR = 0.80, 95% CI 0.59–1.01). Tendency to gain weight in the chest/shoulders (FR = 0.63, 95% CI 0.36–1.08) and waist/stomach (FR = 0.90, 95% CI 0.79–1.02), relative to hips/thighs, was associated with lower fecundability. Moderate PA was associated with increased fecundability (≥5 vs. <1 h/wk; FR = 1.26, 95% CI 0.96–1.65), but there was no dose-response relation. Among overweight/obese women (BMI ≥25 kg/m2), fecundability was 27% higher for vigorous PA of ≥5 versus <1 h/wk (95% CI 1.02–1.57). Conclusion(s):
Various measures of overall and central adiposity were associated with decreased fertility among pregnancy planners. Vigorous PA was associated with improved fertility among overweight and obese women only; moderate PA was associated with improved fertility among all women.

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