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

Authors:
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.

Abstract:

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

Design:
Prospective cohort study.

Setting:
Not applicable.

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

Intervention(s):
None.

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.

Result(s):
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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