[Possible immunologic factors in natural selection of the sexes]

The foetal graft is protected from immunological rejection by the trophoblastic barrier, antigenically neutral. A deficiency of this protective barrier puts the highly antigenic egg contents in direct contact with the maternal organism. The formation of maternal antibodies, and the rejection reaction of the egg graft due to it, probabally explains certain miscarriages. We think that the male fetus must, in these cases, be more antigenic with regard to the graft carrying maternal organism, than the female fetus. A study of 222 pregnancies, with repeated spontaneous miscarriages confirms the clear preponderance of girls, among the non-premature and well-formed children born, and the efficiency of H.C.G. in protecting threatened pregnancies with male fetus.