Prevention of Rh-haemolytic disease: results of the Liverpool "low-risk" clinical trial.

A clinical trial is reported in which Rh-negative primiparae, just delivered of an Rh-positive ABO-compatible infant and in whom fetal cell counts after delivery suggested less than 0.2 ml of circulating fetal blood, were treated with about 200 mug of anti-D gammaglobulin. Three (0.36%) out of 844 women thus treated developed anti-D in the subsequent six months; this is 10% of the incidence in untreated controls. Three (1.8%) out of 171 treated mothers had anti-D at the end of the second Rh-positive pregnancy, and this is 18% of the incidence in controls.Possible reasons for the occasional failure of the treatment are discussed and the results of this trial are compared with those of a previous trial in which 1,000 mug or more of anti-D was given to a different group of mothers. The combined results of the two trials lead to the conclusion that the passive administration of anti-D gammaglobulin after delivery affords in this population of Rh-negative women a 95% protection rate in the postdelivery period and an 89% protection rate by the end of the subsequent pregnancy.