A Rh – negative person, if exposed to Rh +ve blood, will form specific antibodies against the Rh antigens. A special case of Rh incompatibility has been observed between the Rh -ve blood of a pregeant mother with Rh +ve blood of the foetus. 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.
During the delivery of the first child, there is a possibility of exposure of the maternal blood to small amounts of the Rh +ve blood from the foetus. In such cases, the mother starts preparing antibodies against Rh antigen in her blood. In case of her subsequent pregnancies, the Rh antibodies from the mother (Rh -ve) can leak into the blood of the foetus (Rh +ve) and destroy the foetal RBCs.
This could be fatal to the foetus or could cause severe anaemia and jaundice to the baby. This condition is called as erythroblastosis foetulis. Hence it is necessary to check the Rh factor of the blood of pregnant woman.
