USE OF DIFFERENT DOSES OF ANTI-Rh IgG IN THE PREVENTION OF Rh ISOIMMUNISATION

Abstract

The effects of varying doses of anti-Rh immune globulin were investigated in 951 Rh-negative women who had had ABO-compatible Rh-positive infants. 935 mothers had no detectable anti-Rh at delivery but 4 (0.4%) showed subsequent evidence of Rh(D) isoimmunisation. The remaining 16 patients, although treated with the anti-Rh gamma-globulin, had a weak anti-D for the first time at delivery. Sensitisation did not happen when the 1.5 ml. dose (435 μg.) anti-D was given within seventy-two hours of delivery; of the 4 failures 2 were after 1.0 ml. (290 μg. anti-D) had been administered to 254 patients. The material, then eighteen months old, might have lost some of its potency through fragmentation of the gamma-globulin. The smallest dose given was 0.5 ml. (145 μg. anti-D). With this amount, 1 mother out of 172 who had received the injection within forty-eight hours of the delivery of her first ABO-compatible, Rh-positive baby had no detectable anti-D in tests up to six months post partum, but in her second pregnancy evidence of active isoimmunisation (with an incomplete anti-D, titre 1/32) was found at twenty-eight weeks' gestation. Of 260 Rh-negative women given 145 μg. antenatally, at about thirty-four weeks' gestation, and again after delivery of their ABO-compatible, Rh-positive infants, 1 multipara became isoimmunised to the D antigen. Antenatal therapy had no ill-effect on either mothers or babies, and probably offers the best protection, but in the meantime the use of a 1.5 ml. dose, as a single post-partum injection, containing about 450 μg. anti-D, is favoured since there have been no failures with this dose.