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How can Rh or ABO incompatibility cause hemolytic disease in newborns?

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blood disease Peripheral blood smear revealing histopathologic features indicative of a blast crisis in a case of chronic myelogenous leukemia (CML). Blast crisis occurs when one-fifth to one-third of the cells in the blood or bone marrow are immature blood cells, or blast cells. This phase of CML is characterized by fever, weakness, and an enlarged spleen.

Hemolytic disease of the newborn, or erythroblastosis fetalis, occurs when maternal antibodies cross the placenta and destroy fetal red blood cells due to blood group incompatibility.12

Rh Incompatibility

This occurs when an Rh-negative mother conceives an Rh-positive fetus. During labor, fetal red blood cells carrying the Rh antigen enter the maternal circulation, sensitizing her immune system to produce anti-Rh antibodies. In subsequent pregnancies, these IgG antibodies cross the placenta and cause hemolysis of fetal red cells. This is the most severe form of the disease, though it is now largely preventable by administering Rh immunoglobulin to the mother.21

ABO Incompatibility

This occurs when the mother and fetus have different ABO blood types, most commonly when a type O mother carries a type A or type B fetus. While more frequent than Rh incompatibility, the resulting immune reaction is typically much milder. In some cases, concurrent ABO incompatibility can actually protect the fetus from Rh sensitization by destroying fetal cells in the maternal circulation before the mother develops anti-Rh antibodies.23