4.1. Definition. Etiology. Classification
Definition. Isoserological incompatibility (isoimmunization) of maternal and fetal blood is formation of antibodies in maternal blood in response to arrival of fetal antigens incompatible either by blood type or by rhesus factor.
Rhesus immunization is the presence of IgG antibodies in maternal blood as a manifestation of secondary immune response in sensitized patients due to rhesus system incompatibility of maternal and fetal blood.
Fetal hemolytic disease (FHD) is a disease characterized by hemolysis of rhesus-positive fetal erythrocytes under the effect of maternal anti-Rh(D) antibodies entering the circulation through the placental barrier in case of rhesus system incompatibility of maternal and fetal blood. Synonyms: erythroblastosis fetalis, hemolytic jaundice. Etiology. It is known that in normal pregnancy maternal and fetal blood never mix, since the placental barrier is non-permeable for erythrocytes. Antigens of the rhesus factor group and ABO system are located exclusively on the membranes of erythrocytes. Erythrocytic antigens are absent in the blood serum and amniotic fluid.
In rhesus incompatibility the mother's blood is of negative rhesus type, and fetal blood is of positive rhesus type. Presence of antibodies in a woman with rhesus-negative blood indicates sensitization to the rhesus system erythrocytic antigens. Isoimmunization can develop as a result of incompatibility of mater-
nal and fetal blood by other erythrocytic antigen systems (Ag), e.g. by the ABO system, when the mother has O (I) blood type and the fetus - any other. Fetal erythrocytic antigens (AgA and AgB) may pass into maternal bloodstream during pregnancy which causes the production of б- and вAB immune antibodies correspondingly, and the development of Ag-AB (А-б, В-в) reaction in the fetus - hemolysis of erythrocytes.