Introduction: IBD in the mother is associated with higher rates of adverse pregnancy outcomes. However, long-term effects of maternal IBD on childhood growth and development are not known. The aim of this study was to determine the impact of IBD medication exposure in utero on newborn developmental milestones. Methods: We created a prospective cohort of pregnant women at 30 US IBD centers to follow patients through pregnancy and first four years of a child's life. We ascertained IBD medications and disease activity during gestation, complications of pregnancy and delivery, and achievement of developmental milestones. Patients were classified by exposure to drugs taken between conception and delivery: 6MP/Azathioprine (Group A), infliximab, adalimumab, certolizumab (Group B), combination therapy (Group AB). We compared these groups to women who did not take any Group A or B drugs. Developmental milestones achieved by the infant, based on Denver Childhood Developmental Score, were measured by the mother at months 4, 9 and 12 and by the validated Ages and Stages Questionnaire at 1,2,3 and 4 years of age. Follow up is ongoing. Results: 1289 women are enrolled in the study as of Nov 12 2013: 1097 have completed pregnancy, 1039 with live births. There were 215 live births in Group A, 364 in Group B, 137 in Group AB and 323 to unexposed mothers. When compared to the unexposed infants, infants in Group A, B and AB always had equivalent or better achievement of milestones. These results were unchanged when controlled for maternal income and education level. Table 1 lists the milestones in which the exposed infants had better outcomes that the unexposed. Conclusions: Infants with in utero exposure to immunomodulator and biologic therapy did not exhibit developmental delay compared to infants not exposed to these agents, controlling for preterm birth. Overall, developmental scores were similar between exposed and unexposed infants, and scores of exposed infants were slightly higher in some categories. Significant Differences in Developmental Milestones by Drug Exposure