Without prophylaxis, about one in six Rh negative women who deliver a Rh positive infant will develop anti-D antibodies from fetomaternal haemorrhage occurring either during pregnancy or at delivery.1 Since the introduction in 1969 of anti-D immunoglobulin given after delivery the incidence of haemolytic disease of the newborn due to anti-D antibodies has plummeted. In Britain, however, the rate of RhD sensitisation is still unacceptably high, at around 1.5%; in other words, more than 1000 Rh negative women each year develop anti-D antibodies in association with the delivery of a Rh positive infant.

No universal policy exists for postnatal prophylaxis. The standard dose of anti-D immunoglobulin and whether tests are undertaken to assess the size of the fetomaternal haemorrhage vary in different countries. For example, 300 μg anti-D immunoglobulin is the standard dose in the United States, 100-120 μg in Canada, and 200-250 μg in many European countries except Britain and the Republic of Ireland, where the dose is 100 μg (500 IU). Studies have shown that 99% of women have a fetomaternal haemorrhage of less than 4 ml at delivery,2,3 and 100 μg is capable of suppressing immunisation from 5 ml Rh positive red cells. The Medical Research Council's first dosage trial showed that 100 μg anti-D immunoglobulin is as effective as both 260 μg …