Rh antigen is observed on the surface of RBCsof majority (nearly 80%) of humans. Such individuals are called Rh positive (Rh+) and those individuals where this antigen is absent are called Rh negative (Rh-).
Both Rh+ and Rh- individuals are phenotypically normal. The problem in them arises during blood transfusion and pregnancy.
(i) Incompatibility During Blood Transfusion The first blood transfusion of Rh+ blood to the person with Rh- blood causes no harm because the Rh- person develops anti Rh factors or antibodies in his/her blood.
In second blood transfusion of Rh+ blood to the Rh- person, the already formed anti Rh factors attack and destroy the red blood corpuscles of the donor.
(ii) Incompatibility During Pregnancy If father's blood is Rh+, mother blood is Rh- and the foetus blood is Rh+. it will lead to a serious problem. Rh antigens of the foetus do not get exposed to the Rh- ve blood of the mother in the first pregnancy as the two bloods are well separated by the placenta.
But in the subsequent Rh+ foetus, the anti Rh factors (antibodies) of the mother destroy the foetal red blood corpusclesdueto mixing of blood. This result in the Haemolytic Disease of the New Born (HDN), called as erythroblastosis foetalis. In some cases new born maysurvive but will be anaemic and may also suffer with jaundice.
This condition can be avoided by administering anit-Rh antibodies to the mother immediately after the delivery of the first child.
