Grand-maternal lifestyle during pregnancy and body mass index in adolescence and young adulthood: an intergenerational cohort study

To examine associations of healthy lifestyle during pregnancy with body mass index (BMI) and risk of overweight or obesity of grandchildren during adolescence and young adulthood. Our study population included 14,001 grandmother–mother–child triads comprised of participants of two ongoing prospective cohort studies of related individuals. We used self-reported grand-maternal gestational weight gain, diet, physical activity, and smoking during pregnancy to create a lifestyle score ranged from 0 to 12, with a higher score indicating healthier lifestyle. Grandchild BMI was self-assessed in follow-up questionnaires. Compared with individuals whose grandmothers had the least healthy lifestyle during pregnancy, individuals whose grandmothers had the most healthy lifestyle had 0.17 (95% CI 0.01, 0.33; P for trend = 0.05) kg/m(2) lower BMI and 7% (95% CI 2%, 12%; P for trend = 0.001) lower risk of overweight or obesity during adolescence and young adulthood. The inverse associations between grand-maternal lifestyle and BMI in grandchildren were mainly mediated by maternal pre-pregnancy BMI (mediation effect: 64%; P value = 0.001). Overall, maternal BMI, along with maternal socioeconomic status and lifestyle factors in the second and third generations accounted for all of the inter-generational association (mediation effect: 99%; P value < 0.001). The inverse associations of grand-maternal lifestyle with BMI of offspring were not modified by grand-maternal pre-pregnancy BMI, grandchild age, or grandchild gender. Grandchildren of women who had the healthiest lifestyles during pregnancy defined by no excess gestational weight gain, no smoking, a healthy diet and being physically active, were less likely to be overweight or obese in adolescence and early adulthood.