Background. High dose intravenous immunoglobulin has been reported to be advantageous in the treatment of alloimmunization during pregnancy. The mode of action is unknown.
Method. High dose intravenous immunoglobulin was used as the sole prenatal treatment in six severely rhesus(D) sensitized pregnant women. Maternal and fetal anti-D concentrations as well as fetal hemoglobin concentrations were studied. Seven pregnancies in rhesus(D) sensitized women served as controls. They received no treatment because they had milder forms of erythroblastosis fetalis or, in one case, a rhesus(D) negative fetus.
Result. No obvious inhibitory effect of the treatment on maternal anti-D production and transplacental anti-D passage to the fetus was found. The fetal hemoglobin concentrations remained stable at about 80 g/L (hematocrit 27%) in five of six treated patients while there was a significant decrease in the control group.
Conclusion. High dose intravenous immunoglobulin treatment seems to act mainly on fetal red cell destruction rate, possibly by blocking Fc receptor mediated macrophage phagocytosis. We claim that the treatment can successfully be used to prevent further deterioration of fetal anemia in rhesus(D) immunizations if started before severe fetal anemia (hemoglobin concentration < 70 g/L. hematocrit < 23%) and imminent hydrops fetalis arises.