ABO Hemolytic Diseases
ABO hemolytic diseases occur in a very less number of cases, even though materno-fetal ABO incompatibility is very common. The condition is usually seen in O group mothers bearing blood group A or B fetus. It occurs largely in O group mothers because the isoantibodies are largely IgG in nature, which can cross the placenta. It does not occur in mothers with blood groups A or B because natural antibodies are mainly IgM in nature, which does not cross the placenta and sensitize the fetus.
Unlike hemolytic disease of the newborn, the ABO hemo-lytic diseases can occur even in first child even without prior immunization. This is because the ABO disease is caused by naturally occurring maternal isoantibodies.
ABO hemolytic disease is much milder condition than that of the Rh disease. The diagnosis of ABO incompatibility is made by a positive indirect Coombs’ test but a negative direct Coombs’ test. Peripheral blood smear characteristically shows spherocytosis.