To assess whether gestational diabetes mellitus (GDM) can be prevented by a moderate lifestyle intervention in pregnant women who are at high risk for the disease.

Two hundred ninety-three women with a history of GDM and/or a prepregnancy BMI of ≥30 kg/m² were enrolled in the study at <20 weeks of gestation and were randomly allocated to the intervention group (n = 155) or the control group (n = 138). Each subject in the intervention group received individualized counseling on diet, physical activity, and weight control from trained study nurses, and had one group meeting with a dietitian. The control group received standard antenatal care. The diagnosis of GDM was based on a 75-g, 2-h oral glucose tolerance test at 24–28 weeks of gestation.

A total of 269 women were included in the analyses. The incidence of GDM was 13.9% in the intervention group and 21.6% in the control group ([95% CI 0.40–0.98%]; P = 0.044, after adjustment for age, prepregnancy BMI, previous GDM status, and the number of weeks of gestation). Gestational weight gain was lower in the intervention group (−0.58 kg [95% CI −1.12 to −0.04 kg]; adjusted P = 0.037). Women in the intervention group increased their leisure time physical activity more and improved their dietary quality compared with women in the control group.

A moderate individualized lifestyle intervention reduced the incidence of GDM by 39% in high-risk pregnant women. These findings may have major health consequences for both the mother and the child.