Strength training during pregnancy for the prevention of gestational diabetes: A randomized trial in women with overweight or obesity.

INTRODUCTION: Evidence suggests that physical exercise may help prevent gestational diabetes mellitus, although available clinical trials are limited by small sample sizes and low adherence. Strength training may achieve higher adherence rates, but its preventive effect has not been sufficiently evaluated in randomized clinical trials. The objective of this trial is to evaluate the effect of a strength training program in pregnant women with overweight or obesity on the incidence of gestational diabetes mellitus and other outcomes (obstetric and quality of life). MATERIAL AND METHODS: A randomized clinical trial including 209 pregnant women (body mass index ≥25 kg/m2). The intervention group followed a strength training program from gestational weeks 12-14 until week 36 or delivery, combining supervised and home-based sessions. The primary outcome was gestational diabetes incidence; secondary outcomes included gestational weight gain, macrosomia, physical activity, quality of life, and pregnancy symptoms. Trial Registration ClinicalTrials.gov NCT05840497. RESULTS: Forty-eight per cent of participants in the intervention group achieved the adherence target. The intervention group showed lower incidences of gestational diabetes and hydramnios, with absolute risk differences of -5.3% (95% CI: -12.5 to 0.5; p = 0.07) and -4.5% (95% CI: -11.0 to 2.0; p = 0.05), respectively. No significant differences in fetal macrosomia were observed in the intention-to-treat analysis. In the per-protocol analysis, the incidence of GDM was 0% in the adherent intervention group and 7.3% in the control group (risk difference -7.3 [95% CI: -14.3, 3.0]; p = 0.09), and no cases of macrosomia were recorded in the adherent intervention group, compared with 6.3% in the control group (difference -6.3 [95% CI: -13.1 to 4.5]; p = 0.1). The intervention group showed significant improvements in quality of life (mean difference: 8.4; 95% CI: 4.9-11.9; p < 0.001) and reported lower frequency and impact of pregnancy symptoms. No differences were observed in adverse events, including preterm birth. CONCLUSIONS: Strength training during pregnancy improved maternal quality of life and reduced pregnancy-related symptom burden. Although the primary outcome did not reach statistical significance, consistent trends toward lower rates of gestational diabetes and related outcomes, particularly among adherent women, suggest a potential preventive effect that should be confirmed in larger trials.