Epidemiology

Etiology

Highest risk: mother with blood group O; newborn with blood group A or B
Maternal antibodies (anti-A and/or anti-B) against nonself antigens of the ABO system are present even if sensitization has not occurred, so fetal hemolysis may occur during the first pregnancy.
- Combination of predominantly IgM antibodies and late expression of fetal ABO antigens reduces the chances of significant disease.

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