Blood type incompatibility, which may occur between a Type O mother and a Type A father, has been implicated in several common birth defects, including hydatiform mole, choriocarcinoma, spinal bifida, and anencephaly. Several studies suggest that these disorders are caused by maternal blood type incompatibility with fetal nervous system tissue and blood tissue.
Hemolytic (blood destroying) disease of the newborn is the primary condition related to the Rhesus factor. It is a condition that only afflicts the offspring of Rh- women.
Some fifty years ago, researchers discovered that Rh- women, who were missing the Rh antigen, faced a special problem when their babies were Rh+ and carried the Rh antigen on their blood cells. Unlike the major blood type system, where the antibodies to other blood types develop from birth, Rh- people do not make an antibody to the Rh antigen unless they are first sensitized. This sensitization usually occurs when blood is exchanged between the mother and infant during birth, so the mother's immune system does not have enough time to react to the first baby, and so that baby suffers no consequences. However, should a subsequent conception result in another Rh+ baby, the mother, now sensitized, will produce antibodies to the baby's blood type, potentially causing birth defects and even infant death. Fortunately, there is a vaccine that has been developed for this condition, which is given to Rh- women after the birth of their first child, and then after every subsequent birth.
Group A may be protective against cleft lip and palate