In the setting of maternal alloimmunization to antigen(s) on fetal red blood cells, significant fetal anemia may develop, and an intrauterine transfusion may be required. When selecting a blood product for intrauterine transfusion, the priority should be crossmatch compatibility with the mother. Preventing fetal alloimmunization is not practical or necessary. Universal use of O- red blood cells is not appropriate for pregnant women who are alloimmunized to c or e antigens and require an intrauterine transfusion. Essentially, 100% of people who are D- are homozygous for both c and e antigens. Thus, it is logistically impossible to find red blood cells that is D-c- or D-e-, and O+ red blood cells is necessary in the context of maternal alloimmunization to c or e antigens.