Studies in Rh sensitization. VI. A-B-O blood groups and Rh subtypes in sensitized and nonsensitized Rh negative pregnant women.

S LEVINE’ has pointed out, A-B-O incompatibility is less frequent in families with erythroblastotic children due to Rh sensitization than in the general population. That is, an Rh negative mother is less likely to become sensitized to the Rh factor if her Rh positive fetus possesses either the A or B agglutinogen when the corresponding agglutinogen is absent from her own red cells. Wiener2 has ascribed this phenomenon to competition between the A-B and Rh antigens. Another interpretation3 ‘ could be that when fetal cells enter the maternal circulation through a break in the placenta they are rapidly destroyed and eliminated if they belong to an incompatible blood group, while if the fetal cells are compatible with the maternal serum they survive and there is greater opportunity for the Rh agglutinogen to exert its antigenic action.* Whatever the explanation may be, all workers3 ‘ “ who have investigated this problem have been able to confirm Levine’s original observation. One would surmise that group 0, Rh negative women would have less than the average chance of becoming sensitized to the Rh factor during pregnancy because women of group 0 are more likely to have husbands of an incompatible blood group. On the other hand, group A, Rh negative women would have a somewhat greater chance of becoming sensitized because relatively fewer group A women would have husbands belonging to an incompatible group. Accordingly, one would expect the distribution of the A-B-O groups to show a lower incidence of group 0 and a higher incidence of group A among sensitized Rh negative mothers than among the nonsensitized Rh negative mothers. In order to test this prediction, we have analyzed the distribution of the A-B-O blood groups and subgroups in four huusdred fifty-seven sensitized Rh negative women in