Rh factor is a protein (D antigen) present on the surface of the red blood cells in majority (80%) of hum. This protein is similar to the protein present in Rhesus monkey, hence the term Rh. Individuals who carry the antigen D on the surface of the red blood cells are Rh+ (Rh positive) and the individuals who do not carry antigen D, are Rh- (Rh negative). Rh factor compatibility is also checked before blood transfusion.
When a pregnant women is Rh+ and the foetus is Rh incompatibility (mismatch) is observed. During the first pregnancy, the Rh+ antigens of the foetus does not get exposed to the mother’s blood as both their blood are separated by placenta. However, small amount of the foetal antigen becomes exposed to the mother’s blood during the birth of the first child.
The mother’s blood starts to synthesize D antibodies. But during subsequent pregnancies the Rh antibodies from the mother (Rh-) enters the foetal circulation and destroys the foetal RBCs. This becomes fatal to the foetus because the child suffers from anaemia and jaundice. This condition is called erythroblastosis foetalis. This condition can be avoided by administration of anti D antibodies (Rhocum) to the mother immediately after the first child birth.
