Alloimmunization to low and high prevalence blood group antigens: rare causes of hemolytic disease of the fetus and newborn.

Maternal alloimmunization to paternal blood group antigens is the underlying cause of hemolytic disease of the fetus and newborn. Alloantibodies to the major, clinically significant blood group antigens are readily identified by the blood bank which, in turn, allows for appropriate monitoring of the maternal-fetal unit. However, uncommon blood group antibodies, particularly those directed against low and high prevalence antigens, present a more formidable challenge for obstetricians, neonatologists, and transfusion medicine specialists. This article focuses on these unusual blood group antibodies beginning with a classic case presentation. The identification of these antibodies by the blood bank, their monitoring during pregnancy, and the associated implications for transfusion are then discussed. In these cases, a close collaborative partnership is required to ensure an optimal outcome for mothers and their neonates.