ABO HDFN is the most common form of the disease, most frequently associated with anti-A,B in group O mothers who give birth to group A infants. Unlike anti-A and anti-B, which are generally IgM, anti-A,B is more often IgG. Although, ABO incompatibility is a common event, the disease is usually mild and often subclinical.
Rationales to explain the mild nature of ABO HDFN include:
- Fewer A and B antigens on fetal cells
- Poorly developed fetal A and B antigens
- Presence of A and B antigens on cells and tissues other than red cells
Typical symptoms of ABO HDFN include mild anemia and jaundice, usually appearing in the first 24 hours after birth. In rare cases the newborn can exhibit more severe symptoms of Rh HDFN; however, prenatal death is unlikely.