Biologic samples were collected from the mothers and their children as follows: maternal blood (30-35 ml) within 1 day postpartum and umbilical cord blood (30 - 60 ml) collected by delivery room staff immediately after the cord was cut. Members of the research staff transported the samples to the laboratory immediately. The buffy coat, packed red blood cells, and plasma samples were separated and stored at -70°C and then shipped to Columbia University. Placental tissue and meconium were also collected. The placental tissue and meconium were sent to Columbia and stored for future analysis under separate funding.