Mechanisms of isoimmunization. II. Transplacental passage and postnatal survival of fetal erythrocytes in heterospecific pregnancies.

K NOWLEDGE CONCERNING the transpiacental passage of fetal erythrocytes into the maternal circulation is of critical importance for the understanding of immunologic relationships between mother and child and specifically for the mechanisms of Rh isoimmunization. In a previous study1 the phenomenon of transplacental passage was investigated in homospecific pregnancies-i.e., in the absence of maternal antibodies reactive against fetal A, B and Rh antigens, using the immunofiuorescentl ‘ and acid elution technics. It was shown that this phenomenon can be demonstrated with increasing frequency as gestation progresses, so that at delivery at least some fetal cells can be detected in about 50 per cent of the cases; further, in about 1 per cent of these unselected pregnancies, in the population studied, massive transplacental hemorrhage had occured. The present study deals with heterospecific pregnancies and the influence of maternal anti-A and anti-B antibodies on the demonstration and fate of susceptible fetal cells.