Suppression of Early Rhesus Sensitization by Passive Anti-D Immunoglobulin

Abstract

Anti-D immunoglobulin is an effective prophylactic against rhesus isoimmunization. It is generally regarded as ineffective once antibody production has developed though there have been a number of inconclusive reports suggesting it may suppress early sensitization. Anti-D (100μg) was given after delivery of a rhesus (D) positive child to a rhesus (D) negative mother who was shown to have anti-D antibodies at that time by five tests on two separate specimens in two different laboratories and by a weakly positive direct anti-globulin test on the cord blood. In a further pregnancy with a rhesus (D) positive child no antibody was detected by multiple tests including enzyme technique.

Reversal of Rh Alloimmunization

“…Conversely, we have observed a woman with an initial history very similar to the patient described by Tovey and Scott [5], but with a vastly different outcome. Patient Pa, a participant in the Western Canada Rh Pre vention Clinical Trial [6], had no demon strable Rh antibody when screened by a sen sitive two-stage manual enzyme technique (P2) [7] at 8 and 28 weeks' gestation and immediately after delivery of an Rh-positive baby.…”

“…Of the 29 women who became Rh immunized during the 3rd trimester, 24 had Rh antibodies detected RhIG given to each of these women after delivery was not stated. Tovey and Scott [5] report 1 woman who had an Rh antibody demonstrable weakly by IDAT and two en zyme (papain and ficin) red cell manual techniques immediately after delivery of her first Rh-positive baby, just before adminis tration of RhIG. 3 years later, on 9 occasions during and at the end of her second Rhpositive pregnancy, no Rh antibody could be detected using enzyme, antiglobulin, albu min, and saline techniques.…”

“…Because of the report of Tovey and Scott [5] and our exactly opposite experience with Pa, we believe it to be of interest and of importance to report the results of a clinical trial carried out between 1969 and 1977, in which we administered RhIG in an attempt to suppress or reverse weak early Rh immu nization. We also report our observations of the natural course of weak Rh immunization in women not treated with RhIG in the era before Rh prevention and in women given standard Rh prophylaxis, some at 28 weeks' gestation and after delivery, others only after delivery in the era after Rh prevention.…”

Fetomaternal Transplacental Hemorrhage during Pregnancy and after Delivery

“…De Silva et al's [5] observations that 0.28 ml of red cells produced a secondary response in 14 of 14 volunteers would indicate that the minimal dose required is less than 0.28 ml. Jakobowicz et al 3 [ 101 observations that 1 of 2 male volunteers developed primary Rh immunization after receipt of 0.024 ml of Rh-positive red cells would indicate that the dose required to produce a secondary response in some individuals may be less than 0.024 ml.…”

Fetomaternal Transplacental Hemorrhage during Pregnancy and after Delivery

“…Because of reports that administration of Rh immune globulin (RhIG) might reverse weak Rh immunization [1][2][3], the Rh Laboratory reviewed its experience, from 1969 to 1977, with a clinical trial of attempts to suppress weak primary Rh immunization (an Rh antibody initially detectable only by a two-stage papain-treated red cell technique (P2) or detectable by P2 and very weakly, at or after 6 min, by a sensitive, timed, indirect antiglobulin technique (IDAT) [4]. We compared the results of the clinical trial with the course of Rh immunization in 2 other groups of Rh-negative women, initially presenting with weak Rh antibodies which met the same criteria [4] ; all women followed from 1944 to 1967 in the pre-Rh prophylaxis era, and all women followed from 1968 to 1983 who were given RhIG at 28 weeks' gestation (300 pg i.m.…”