ABO and fetal erythroblastosis: Alloimmunization is the production of antibodies from antigens that are not specific to that individual, and we know that several antigens can cause HDFN, such as those from the ABO, Rh, Kell, Duffy, MNS, Kidd, Diego, Colton and other systems.(7) In the Rh system, the D antigen is the most immunogenic and is usually responsible for 90% of cases of hemolytic disease in our setting.(5)