Question

Why does the first Rh^+ve child born to an Rh⁻ mother safe while the subsequent Rh⁺ children may suffer from the disease?

Answer 1

The Rh factor is an antigen present on the RBCs of Rh⁺ individuals.

(i) During the first pregnancy, the Rh⁻ mother carries an Rh⁺ foetus. Some foetal RBCs may leak into the mother's blood at the time of delivery. The Rh antigens on these cells stimulate the mother's immune system to produce anti-Rh antibodies and memory cells.

(ii) The first child is generally safe because the sensitisation of the mother's immune system occurs only around or after delivery, and enough antibodies are not present to harm the foetus.

(iii) During a subsequent pregnancy with an Rh⁺ foetus, the memory cells of the mother give a rapid secondary response, and the anti-Rh antibodies cross the placenta and destroy the foetal RBCs. This causes severe haemolytic disease of the newborn (erythroblastosis foetalis).

Hence, the first Rh⁺ child is protected while the subsequent Rh⁺ children may suffer from the disease.