Relationship between blood groups and sex ratio of the newborn

The examinations prove that due to the foetomaternal blood group incompatibility the sex ratio of the newborn will be higher. The most probable explanation for this fact is that the foetomaternal blood group incompatibility exerts a negative effect on the X chromosome, in consequence of which the elimination rate of the zygotes fertilized by Y chromosome-carrying spermia decrease and thus the sex ratio will be higher. The highest sex ratio was found among the D-negative newborns of D-positive mothers (172.7), whereas the lowest one among the D-positive children of D-positive mothers (113.5). The incompatibility existing in the other antigens of Rh-system and in the ABO-system also elevated the sex ratio to a minor degree.