Controlled trial of various anti-D dosages in suppression of Rh sensitization following pregnancy. Report to the Medical Research Council by the working party on the use of anti-D-immunoglobulin for the prevention of isoimmunization of Rh-negative women during pregnancy

Abstract

In a controlled trial phials containing 200 mug, 100 mug, 50 mug, or 20 mug of IgG anti-D were given to nearly 2,000 D-negative primiparae whose infants were D-positive and ABO-compatible. Only mothers whose serum lacked anti-D were included and the dose of anti-D was always given within 36 hours of delivery. Each phial contained the same total volume of immunoglobulin and the particular dose given to any patient was not known to the clinician. The anti-D content of the phials was estimated three times during the course of the trials and remained fairly constant. Six months after delivery the incidence of a positive indirect antiglobulin test result, indicating the presence of anti-D, in the four dose groups (with about 450 women in each group) was as follows: 0.22%, 0.23%, 0.44%, and 1.35%. The trend towards an increase in the frequency of failures as the dose decreases was significant at the level of P=0.02.In each dose group about 200 women were followed to the end of a second pregnancy with a D-positive infant. The failure rates (in order of decreasing dosage) as judged by a positive indirect antiglobulin test result at the second delivery were as follows: 1.5%, 1.1%, 1.5% and 2.9%. The differences between the dose groups were not statistically significant. The overall failure rate (1.7%) was about one-tenth of that expected in an untreated series. Though the results failed to prove any differences in success rates between doses of 200, 100, 50, and 20 mug of anti-D, they do suggest, in conformity with other evidence, that a dose of 20 mug is suboptimal for routine use. The results support the belief that a dose of 100 mug is adequate.