Risk of gestational diabetes by aerobic and resistance exercise during the first and second trimesters.

Objective: While some studies have shown that exercise reduces the incidence of gestational diabetes mellitus (GDM), there is limited evidence on whether aerobic or resistance exercise is more beneficial. This study aimed to examine the rate of GDM according to the type of exercise during early pregnancy. Study design: We analyzed data from the Nulliparous Pregnancy Outcomes Study: Monitoring Mothers-to-Be (nuMoM2b), a prospective cohort of individuals enrolled during the first and second trimesters. We excluded participants with pregestational diabetes or delivery <20 weeks. The primary exposure was either aerobic or resistance exercises in the first or second trimester. For each trimester, the metabolic equivalent of task hours per week (MET-h/week) was calculated for each exercise. Participants were grouped as follows: "Aerobic exercise" (≥7.5 MET-h/week from aerobic exercises), "Resistance exercise" (≥2 times/week from resistance exercises), "Both types of exercise" (≥7.5 MET-h/week from aerobic exercise and ≥2 times/week from resistance exercises), and "Insufficient exercise" (≤7.5 MET-h/week from aerobic exercise and ≤2 times/week from resistance exercises). Our primary outcome was GDM. Adjusted relative risks (aRRs) with 95% confidence intervals (95% CIs) were calculated using modified Poisson regression, adjusting for potential confounders. Results: In both the first and second trimesters, analyses included 9049 individuals. In the first trimester, individuals who performed aerobic exercise (aRR, 0.75; 95% CI, 0.60-0.93) had a lower risk of GDM compared with those with insufficient exercise. In the second trimester, those who performed aerobic exercise (aRR, 0.78; 95% CI, 0.63-0.97) and both types of exercise (aRR, 0.48; 95% CI, 0.25-0.93) had a lower risk of GDM. Resistance exercise alone, compared to insufficient exercise and compared to aerobic exercise alone, was not clearly associated with significant differences in GDM. Across trimesters, we did not observe increased risks of small for gestational age birth, preterm birth, and preeclampsia. Conclusion: Aerobic exercise during the first and second trimesters and combined aerobic/resistance exercise during the second trimester were associated with a lower risk of GDM compared to insufficient exercise. Future intervention studies focusing on exercise to reduce the risk of GDM are warranted.