The Nature of the Determinants of Rhesus Isoimmunization

The circumstance necessary for the development of haemolytic disease of the newborn, the marriage of an Rh(D)-positive man to an Rh(D)-negative woman, is found in about 14 per cent, of all marriages, but only a small proportion of these result in an affected infant. This is because only about one woman of every twenty at risk develops immunity to her Rh-positive infants, for once immunity has developed all subsequent Rh-positive babies will be affected. It is not known why one mother should develop antibodies when nineteen fail to do so. ABO incompatibility between baby and mother reduces the risk still further, but as two-thirds of foetuses are compatible, this provides only a part explanation and has little bearing upon the main issue.