The mechanism of transfer, in cases of erythroblastosis fetalis, of incompatible fetal red blood cells to the mother and of maternal blood with antibody to the fetus, was observed especially well in 2 cases in which the infants were born alive.
The two placentas showed occlusion of peripheral blood vessels of many villi and trunks by agglutinated red blood cells and fibrin. Associated with the vascular thromboses, there were, in places, necrosis of the walls and of regional tissues with rupture and hemorrhage of fetal blood, containing numerous intact nucleated red blood cells, into regional intervillous spaces. Through the broken surfaces, adjacent maternal blood was in contact with the fetal circulation.
A more accurate designation for "erythroblastosis fetalis" would be "transplacental erythrocytotoxic anemia."