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The introduction of biologic therapy with therapeutic monoclonal antibodies to the treatment strategies of inflammatory bowel disease (IBD) has significantly changed the way clinicians practice. Antibodies are cleared differently than small molecules, and knowledge about the pharmacology and immunology of immunoglobulins is helpful when using these agents in women preconception and during pregnancy. The most commonly used antibody therapies in patients with IBD are IgG1 molecules, but others are under development. When treating patients who are pregnant or contemplating pregnancy, it is important to remember that immunoglobulin G (IgG) is the predominant means of fetal immunity and that it is transported across the placenta. This transport happens in a linear fashion as the pregnancy progresses, with the largest amount transferred in the third trimester. Preferential transport occurs for IgG1, followed by IgG4, and IgG3 with IgG2 being the least detected. Understanding the mechanism for immunoglobulin transfer will help to understand how to minimize risk of exposure of the fetus to the therapeutic monoclonal antibody bothin uteroand after delivery.