There are more than 20 genetically determined blood group systems known today, but the ABO and Rh systems are the most important ones with significant clinical implications in cases of blood transfusion & pregnancy. This is due to the fact that all blood groups are not compatible with each other & mixing of incompatible blood groups may frequently lead to clumping or agglutination of blood cells, which is dangerous & may prove fatal.

Roughly, about 85% people are estimated to be Rh positive. However, if a woman who is Rh negative and a man who is Rh positive conceive a baby, there is a considerable potential for hemolytic disorders to arise as the baby developing inside the Rh-negative mother's body may have Rh-positive blood, inherited from the father. This is termed as Rh Incompatibility.

In case of first pregnancy, Rh incompatibility usually isn't a problem because unless there's some sort of abnormality, the fetus's blood does not normally enter the mother's circulatory system during the course of the pregnancy. However, during delivery, the mother's and baby's blood can intermingle. If this happens, the mother's body recognizes the Rh proteins as a foreign substance and can begin producing antibodies against it. These antibodies are introduced into mother's blood. An Rh-negative pregnant woman can be exposed to the Rh antigens by blood transfusions with Rh-positive blood, miscarriage, or an ectopic pregnancy i.e. from a pregnancy resulting from gestation elsewhere than in the uterus.

Rh antibodies are harmless until the mother's second or later pregnancies. If she ever again carry's another Rh-positive child, her Rh antibodies will recognize the Rh antigens on the surface of the baby's blood cells as foreign, and pass into the baby's bloodstream and attack those cells. This can lead to swelling and rupture of the baby's red blood cells leading to reduction in baby's blood count.

Prevention and Treatment:

Such complications may be prevented by proper pre-martial or importantly, pre-conception blood typing & counseling. By knowing your own & your partner's blood type, proper preventive measures can be taken to avoid potential medical ramifications. Fortunately, significant medical advances have been made so far to help prevent complications from Rh incompatibility and to treat any newborn affected by such Rh diseases.