Is there a reproductive compatibility or incompatibility regarding the blood groups?
Studies have shown a significant excess (87%) of ABO incompatible couples in 102 persistently sterile marriages. The same researchers also found that in 7 couples with markedly delayed fertility, the 9 children that did result were all blood type O, and hence would have been compatible with the mother. The authors suggested that the infertility was due to the presence of antibodies in the secretions of the mother’s genital tract, or incompatible sperm from the father. Several older studies have shown childlessness more frequent among blood type A and B women than among AB or O, while a 1965 study showed an increased proportion of type O children in families with more than one child. All these studies consistently showed that if the father possesses an A antigen which the mother does not, there is a marked selection against the survival of the A offspring. There is a marked tendency of blood type O babies of blood type O mothers to be male as opposed to blood type A babies of type A mot
