A prospective study of pregravid physical activity and sedentary behaviors in relation to the risk for gestational diabetes mellitus.

BACKGROUND Although gestational diabetes mellitus (GDM) has been associated with substantial adverse health outcomes for both mothers and offspring, few modifiable risk factors for GDM have been identified. METHODS We conducted a prospective cohort study among women in the Nurses' Health Study II to assess whether the amount, type, and intensity of pregravid physical activity and sedentary behaviors are associated with GDM risk. The analysis included 21,765 women who reported at least 1 singleton pregnancy between 1990 and 1998. Physical activity and sedentary behaviors were assessed through validated questionnaire. RESULTS We documented 1428 incident GDM cases. After controlling for body mass index, dietary factors, and other covariates, there was a significant inverse association between vigorous activity and the risk of GDM. The multivariate relative risk (RR) comparing the highest with the lowest quintile of vigorous activity was 0.77 (95% confidence interval [CI], 0.69-0.94) (P = .002 for trend). Among women who did not perform vigorous activity, brisk walking pace was associated with significantly lower GDM risk (RR, 0.66; 95% CI, 0.46-0.95) compared with an easy pace. Women who spent 20 h/wk or more watching television but did not perform vigorous activity had a significantly higher GDM risk than women who spent less than 2 h/wk watching television and were physically active (multivariate RR, 2.30; 95% CI, 1.06-4.97). CONCLUSION Our prospective study provides strong evidence that regular physical activity before pregnancy is associated with lower GDM risk.