Alloimmunity in pregnancy is the basis for two of the major complications of pregnancy in transfusion medicine: hemolytic disease of the fetus and newborn (HDFN), and fetal and neonatal alloimmune thrombocytopenia (FNAIT). Use of Rh(D) immune globulin has dramatically reduced the incidence of HDFN in Rh(D)-mismatched pregnancies. Treatment of HDFN may involve intrauterine transfusion, with fetal and neonatal survival rates of 70% to 90%. Treatments for FNAIT include immune globulin, steroids, or in severe cases, intrauterine platelet transfusions. Transfusion medicine is central to the management of pregnancy-associated complications such as postpartum hemorrhage, parvovirus B19 infection, hemoglobinopathies, and aplastic anemia.