This longitudinal prospective study takes advantage of the resources provided by Project Viva, an ongoing prospective cohort study of pregnant women and their infant offspring among members of Harvard Pilgrim Health Care, a large managed care organization in New England. Data already available from Project Viva include detailed dietary data on mother and infant, along with data on anthropometric, social, environmental, demographic, economic, psychological, and lifestyle variables. The study will follow the Project Viva cohort until ages 3 to 4 years.