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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.

The IgG subclass distribution of anti Rh antibodies (anti-D, 'anti-Du', anti-c, anti-E), anti-Kell and anti-Duffy (anti-Fya) antibodies was measured by two haemagglutination techniques on microtitre plates. The first technique involved rabbit subclass specific antisera which were used to agglutinate red cells previously reacted with the patients' antibodies at high concentration. The second, which was more sensitive, had an additional step by introducing sheep anti-rabbit antibodies (sandwich technique). By the sensitive sandwich technique we revealed, for anti-D antibodies: IgG1 8/19, IgG3 1/19, IgG1/IgG3 8/19, IgG1/IgG2/IgG3/IgG 41/19, IgG1/IgG4 1/19; for the Du reactive anti-D antibodies: IgG1 1/8, IgG1/IgG3 1/8, IgG1/IgG3/IgG4 6/8; for the anti-E antibodies: IgG1/IgG2/IgG4 2/3, IgG1/IgG2/IgG3/IgG4 1/3; for the anti-c antibodies: IgG1 2/5, IgG3 1/5, IgG1/IgG3 1/5; for the anti-Kell antibodies: IgG1 9/20, IgG1/IgG3 1/20, IgG1/IgG4 8/20, IgG1/IgG3/IgG4 2/20; and for anti-Duffy antibodies: IgG1 1/8, IgG1/IgG4 7/8. These results are partly at variance with previously published results.

During routine ante-natal testing during the period 1953-73 anti-c was found in the serum of 63 women. Twenty-four of them had received blood transfusion previously and of these 22 were multigravidae. In 39 women pregnancies alone were responsible for the immunization. The anti-c titres of the 42 women giving birth to c positive babies showed that the probability of developing haemolytic disease increases with higher titres. But low titres by no means exclude the existence of such disease. Among the 42 c positive babies 32 had a positive direct antiglobulin test. Some of the affected infants had a serious degree of haemolytic disease.

The frequency of irregular blood group antibodies detected for the first time in pregnant women during the period 1975-80 has been examined. Whereas Rh(D)-negative gravidae in Norway are examined immuno-hematologically three times during pregnancy, Rh(D)-positive women are tested once only, usually early in pregnancy. Nevertheless, about one-third of the new cases of immunization within the Rh system were found in the Rh-positive women. In the latter, anti-E and anti-c were the Rh antibodies most frequently encountered. Among other irregular antibodies which can cause hemolytic disease of the newborn (HDN), those of the Kell and Duffy systems are the ones second in frequency and clinical significance to the Rh antibodies. In the present series about 40% of the new cases of immunization within the Rh, Kell and Duffy systems were found in Rh-positive women. This proportion would undoubtedly have been greater if also the Rh-positive women had been retested for the presence of irregular blood group antibodies towards the end of the gestation. Such a retesting of Rh-positive gravidae is desirable both for a better prediction and early diagnosis of HDN and to facilitate the procurement of compatible blood if the woman should need an emergency blood transfusion.