['Does a 12-week exercise program prevent gestational diabetes and improve insulin resistance in healthy pregnant women with normal body mass index (BMI)?', 'Randomised, controlled trial with concealed allocation and blinded outcome assessment.', 'Two University hospitals in Norway.', 'White adult women with a single fetus. High-risk pregnancies or diseases that would interfere with participation were exclusion criteria. Randomisation of 855 participants allocated 429 to the exercise group and 426 to a control group.', 'Both groups received written advice on pelvic floor muscle exercises, diet, and lumbo-pelvic pain. In addition, the intervention group participated in a standardised group exercise program led by a physiotherapist, once a week for 12 weeks, between 20 and 36 weeks gestation. The program included 30-35 minutes low impact aerobics, 20-25 minutes of strength exercises using body weight as resistance and 5-10 minutes of stretching, breathing, and relaxation exercises. They were also encouraged to follow a 45-minute home exercise program at least twice a week. The control group received standard antenatal care and the customary information given by their midwife or general practitioner.', 'The primary outcomes were the prevalence of gestational diabetes, insulin resistance estimated by the homeostasis model assessment method (HOMA-IR), and fasting insulin and oral glucose tolerance tests at baseline and at the end of the training period. Fasting and 2-hour glucose levels were measured in serum by the routine methods. Gestational diabetes was diagnosed as fasting glucose level 2-hour value ≥7.8mmol/L. Secondary outcome measures were weight, BMI, and pregnancy complications and outcomes.', '702 participants completed the study. At the end of the 12-week program, there was no difference in the prevalence of gestational diabetes (25 (7%) of intervention group compared with 18 (6%) of control group), HOMA-IR (-0.15, 95% CI -0.33 to 0.03), or oral glucose tolerance tests at 2 hours (-0.13mmol/L, 95% CI -0.28 to 0.03) between the groups. Fasting insulin was significantly lower in the intervention group by 1.0 international units/mL (95% CI -0.1 to -1.9). The groups did not differ significantly on any of the secondary outcomes. Adherence to the exercise protocol in the intervention group was 55%. A per protocol analysis of 217 women in the intervention group who adhered to the exercise program demonstrated similar results with no difference in prevalence of diabetes.'] Does a 12-week exercise program performed during the second trimester prevent gestational diabetes in healthy pregnant women?