Unmanaged alloimmunization in pregnancy can be associated with deleterious fetal complications, including hemolytic anemia, hydrops, and intrauterine fetal demise. The pathophysiology of this disease includes the development of maternal antibodies against fetal erythrocyte antigens after a history of exposure to those antigens in a prior pregnancy. Those antibodies cross the placenta and lead to hemolytic disease of the fetus and newborn. Rh(D) alloimmunization is the most frequent cause of alloimmunization during pregnancy. It occurs in the setting of an Rh(D)-negative mother and an Rh(D)-positive fetus with a history of exposure in a prior pregnancy. In the presence of an alloimmunized pregnancy, paternal genotype should be determined. In this case, the father of the baby is heterozygous, so fetal genotype should be determined. This is most commonly performed by amniocentesis and polymerase chain reaction.

Anti-D immune globulin (B) is indicated for the prevention of alloimmunization in susceptible pregnancies but is not indicated once alloimmunization has already occurred. Middle cerebral artery Doppler (C) is a method of predicting fetal anemia and may be used for monitoring if the fetus is Rh(D) positive. Routine prenatal care (D) is indicated if the fetus is Rh(D) negative, which has not yet been confirmed.