Fifteen years' experience with post-partum Rh prophylaxis in Norway (1969-83): incidence of new cases of anti-D and other clinically important blood group antibodies in pregnant women.

The effect of the post-partum Rh prophylaxis in Norway was studied. From a preprophylaxis incidence of 47.4 new cases of Rh(D) immunization per 10,000 pregnant women the incidence fell to 8.9 per 10,000 in 1982-83, and further to 7.1 per 10,000 in 1986. In the period 1980-83 58 per cent of the new antibodies within the Rh system were anti-D, while 42 per cent had other Rh specificities occurring in Rh(D) positive women. The incidence of new immunizations within the Kell and Duffy systems was also studied. Fifty per cent of the antibodies detected within the three blood group systems occurred in Rh positive gravidae. It is known from other studies that at least 30 per cent of pregnant women who develop blood group antibodies do so after the first assay is performed. Therefore the number of antibodies found in Rh positive women would increase significantly if they too were retested towards the end of pregnancy.