This study will examine effects of everyday life stress and obesity on immune responses to influenza virus vaccine (the flu shot) during pregnancy. Following vaccination, antibody levels against influenza (the flu) increase. Higher antibody levels indicate better immune protection from influenza. In addition to providing protection from the flu for yourself, being vaccinated during pregnancy may protect your baby from the flu during the first six months of life during which time infants cannot be vaccinated. Our primary goals are to determine whether greater life stress and obesity reduce 1) antibody responses to the flu shot in women and 2) antibody levels in the newborn at the time of delivery.