Inflammatory bowel disease (IBD) affects women during their reproductive years and 25% become pregnant after an initial diagnosis of IBD. New data suggest that babies are born not-sterile, and bacteria, also known as microbiome, are passed from the pregnant mother to the fetus in the womb. The make-up of these initial bacteria significantly contributes to the development of newborn’s immune system and may affect the risk of diseases later in life. While it is well established that patients with IBD have an altered microbiome, no data exist on the types of bacteria passed from pregnant women with IBD to their babies or on the role these bacteria play in the development of baby’s immune system. Therefore, we propose to transplant the stool of newborn babies born to women with and without IBD to germ-free mice, known to have underdeveloped immune system, and characterize the changes in their immune system before and after the transplantation. We will also track particular bacteria that were successfully engrafted into germ-free mice and determine their effect on the maturation of immune responses. This research could inform future clinical trials of microbial manipulation during pregnancy as a possible strategy to prevent IBD risk transmission.