The term ‘Rh factor’ stands for Rhesus factor. In biology it is known as a group of antigens which exists in the red blood cells of human beings. The Rhesus system was discovered by Landsteiner in 1940 while doing research on the Rhesus monkeys regarding blood groups. The Rhesus factor in human blood involves reaction with the blood of the Rhesus monkey. In fact it refers to the presence or absence of substances or factors in the red cells. There are half a dozen Rhesus factors, but ‘D’ factor is especially important in this regard. In majority of people this factor is present and they are known as Rhesus positive (Rh+). But about 15% of the human population, however, inherits blood that lacks in Rhesus factor. Their Rh factor is thus described as Rhesus negative (Rh-).
There is no naturally occurring anti-Rh antibody. But if by mistake Rh+ blood is transfused into a Rh- person’s system, it can stimulate production of an antibody against the foreign ‘D’ factor and this antibody may eventually destroy the donated cells. The reaction is very slow in first transfusion, but becomes fierce in second or subsequent ones.
The Rh factor plays a significant role during pregnancy. Some or all of the children of an Rh- mother and an Rh+ father may inherit the factor from the father. When a Rh- mother conceives a Rh+ baby and the blood supplies of the mother and the baby mix during the delivery resulting in some of the baby’s blood mixing with the mother’s blood, her blood may form antibodies against the Rh factor. Although these antibodies disappear after a few months, the mother is sensitised. In subsequent pregnancies, she may produce anti-Rh bodies which would attack the baby’s red cells. As a result the child might be stillborn or may die at birth due to a heart failure or a damaged brain or jaundice. In extreme cases so many red blood cells are destroyed that the foetus may die before birth.
It is possible to overcome the problem with an exchange transfusion, the gradual removal of the baby’s blood, a few millilitres at a time and its replacement with Rh negative blood. In this way, some 95% of the affected babies can be saved.
The condition brought about by the Rh incompatibility is known as ‘hemolytic disease’ of the neonate. The risk has been lessened by the development of a vaccine made from the anti-Rh antibody (known as Rh immune globulin). If this is administered to the mother within 24 hours of the birth of an Rh+ baby, it removes from her blood any Rh+ cells which may have seeped in. This saves her from becoming sensitised.
The vaccine is now given as a preventive measure to Rh- mothers and it is repeated at each pregnancy. Thus due to these precautions the number of deaths of newborn babies caused by haemolytic disease is falling rapidly.