Blood groups and histocompatibility antigens in habitual abortion.

: Forty-six couples with at least two consecutive abortions were examined. The morphological and the functional clinical check-ups were constantly negative. In all the couples a karyotype analysis was carried out including an investigation of C and/or G bands. The phenotypes of ABO, Rh, MNSs and HLA-systems were also determined. No significant difference was observed in the distribution of ABO phenotypes between males and females, or between subjects with abortions and controls. Regarding the Rh system, the most important findings are the absence of phenotypes with the E allele in double dose, the reduction of the frequency of the CCDee phenotype and the increase in the frequency of the ccDEe phenotype. Concerning MNSs system, an increase in the frequency of the phenotypes with the S allele in double dose is observed. Females with habitual abortions show a higher incidence of Bw35 as compared both to males and to the controls. No significant differences were observed for other antigens. The persistence of a genetic disequilibrium both in the Rh and the MNSs systems suggests that the selection might act against certain antigenic combinations, independently from the state of materno-foetal compatibility. Though preliminary, our data seem to give some support to this hypothesis. They also suggest that Bw35 antigen may be important in human reproduction.