In 1939, two scientist discovered an unknown element in the blood of teh Rhesus monkey. The RH factor is the antigen or protein attached to the Red Blood Cell. Rh is the protein substance present in the cells of most people, capable of inducing intense antigenic reactions. It is present in 85% of caucasians with a slighty higher percentage among blacks and orientals. .
Rh incompataibility exist only if the mother is Rh negative and the baby is Rh positive, and if during pregnancy some of the Rh positive blood of the baby finds its way through the placenta and into the bloodstream of the mother. Antibodies develop to fight the foreign Rh positive factor. These antibodies will also be present if at some time she has had a blood transfusion from an Rh positive donor or she had a miscarriage, abortion or aminocentesis in which the placenta was injured.
Once the antibodies have developed they pass through the placenta and into the baby's bloodstream where they can cause damage to the red blood cells. First babies are rarely effected (barring the transfusion and miscarriage factors) because of the length of time needed to produce the anti-bodies. The child is usualy born before there are sufficent antibodies to cause damage.
When a sensitized woman, (one who has developed antibodies) becomes pregnant with an Rh positive child, her antibodies attack the Rh positive protein which is attached to the baby's Red Blood Cells, thus destroying them. The baby suffers from the effects of anemia. Trying to compensate for this, immature Red Blood Cells are released into the baby's blood stream. These are called erythroblast, resulting in the condition Erythroblastosis fetalis also called Hydrops Fetalis. Enlargment of the liver and spleen, generalized edema, Jaundice and even death can occur.
If Rh incompatibilty is a possibility, antibody titers will be done at the initial prenatal visit and at twenty-four, twenty-eight, thirty-two and thirty-six weeks.