Association between the intensity of exercise in the first trimester and early second trimester and the risk of gestational diabetes

Abstract Objective Although some studies show that exercise decreases the incidence of gestational diabetes mellitus (GDM), the optimal exercise intensity during pregnancy remains unclear. We examined GDM risk according to exercise intensity in pregnant individuals. Methods We analyzed data from the Nulliparous Pregnancy Outcomes Study: Monitoring Mothers‐to‐Be (nuMoM2b), a prospective study enrolling nulliparous individuals in the first trimester. Participants with pregestational diabetes or delivery before 20 weeks were excluded. Exercise intensity during the first (6–13 weeks’ gestation) and early second (16–21 weeks’ gestation) trimesters was categorized by metabolic equivalent of task hours per week (MET‐hr/week) as none, low intensity (< 7.5), moderate intensity (7.5–14.9), or high intensity (≥ 15). The primary outcome was GDM; secondary outcomes included preeclampsia, gestational hypertension, preterm birth, small‐for‐gestational‐age birth, and stillbirth. Adjusted relative risks (aRRs) with 95% confidence intervals (CIs) were calculated using a generalized linear mixed‐effects model with a Poisson distribution and robust error variance, controlling for the random effects of individuals and potential confounders. Results In the first trimester ( n = 9049), 30.2% of participants reported no exercise, 23.9% engaged in low‐intensity exercise, 19.0% in moderate‐intensity exercise, and 26.7% in high‐intensity exercise. In the early second trimester, 29.7% reported no exercise, 26.5% had low‐intensity exercise, 20.5% moderate‐intensity exercise, and 23.3% high‐intensity exercise. Compared with no exercise, high‐ and moderate‐intensity exercises were associated with a lower risk of GDM (aRR 0.63 [95% CI 0.51–0.78] and aRR 0.81 [0.68–0.96]), while low‐intensity exercise showed no significant association with GDM risk reduction. Moderate‐intensity exercise was also associated with a lower risk of preeclampsia. Notably, no exercise intensity was associated with an increased risk of any adverse pregnancy outcome. Conclusion High‐ and moderate‐intensity exercises during early pregnancy were associated with a lower risk of GDM compared to no exercise. These findings support the need for interventional trials to evaluate whether increasing exercise intensity during pregnancy can effectively prevent GDM.