This report describes the case of a patient with a history of HDN comp
licated by fetal losses, in which the alloantibody in this particular
pregnancy did not appear to cause HDN in utero. No protective HLA-DR a
ntibodies could be demonstrated, and transport of IgG across the place
nta appeared to be normal. The infant's red cells possessed a normal D
antigen and his mononuclear phagocyte system appeared unimpaired. How
ever, the number of molecules of IgG bound in vivo per fetal red cell
was below the level usually associated with significant haemolysis and
HDN.