Abstract

Seeking a relationship between blood groups and successful pregnancy, Linn's group carried out an analysis using the medical records of 11,659 women. They found a significantly higher frequency of bleeding during pregnancy among Rh(+) women, when compared with Rh(-) women. However, they concluded that this relationship is not important because it is due to confounding variables and not to the mother's phenotype. It should be noticed that although we cannot say that there is a causal relationship, there is definitely a relationship between Rh phenotype and bleeding during pregnancy in the study published by Linn and co-workers. This relationship is important from an evolutionary standpoint and it suggests that the natural selection could be working more intensely against Rh(+) than against Rh(-) mothers.