Invited commentary: How early in life does the risk of obesity originate?

Mothers and fathers influence the risk of obesity in their children through genetic, environmental, and behavioral factors. Unique to the mother, however, is the intrauterine environment in which the fetus develops, and it is during this time in the uterus that the risk of later obesity in the child may develop. In this issue of the Journal, Fleten et al. (Am J Epidemiol. 2012;176(2):83-92) investigate whether the intrauterine environment plays a role in the development of adiposity by comparing the association between maternal prepregnancy body mass index (BMI; measured as weight in kilograms divided by height in meters squared) and offspring BMI at 3 years of age with the paternal-offspring association at the same age in the Norwegian Mother and Child Cohort Study. In that large study of stable, relatively healthy and well-educated families, significant differences in maternal-offspring and paternal-offspring BMI associations were not identified. These findings are interpreted as indicating that the influence on the child's BMI of the intrauterine environment is less important than that of genetics and shared environment. Results from that study suggest that further consideration should be given to the specificity of the fetal overnutrition hypothesis in terms of which aspects of the intrauterine environment may influence offspring adiposity and when across the life course these effects may manifest themselves.