Incidence of Rh immunization between 1981 and 1992.

Background: The Institute of Immunohaematology has had an Rh clinic at the Nowrosjee Wadia Maternity Hospital since 1957. Between then and 1977, 5% Rh-negative women produced Rh antibodies. Between 1978 and 1980, the rate of immunization was reduced to 3.3%. In the present study we determined the incidence of Rh immunization between 1981 and 1992.

Methods: ABO and Rh grouping was carried out by standard methods on 139,635 samples collected from antenatal women. Six thousand nine hundred and fourteen (5%) Rh-negative women were screened for Rh antibodies using an enzyme technique. Analysis was carried out by dividing the data into four groups, each of three years duration.

Results: The number of women attending the antenatal outpatients increased steadily but the frequency of Rh-negativity remained at approximately 5%. The rate of Rh immunization among Rh-negative women declined from 3.1% during 1981-83 to 1.7% during 1990-92. The rate among pregnant women dropped from 0.16% to 0.09% and this was statistically significant (p < 0.05). The incidence of Rh immunization among Rh-negative women increased from 0.4% in the first pregnancy to 17.5% after four or more pregnancies (p < 0.01). Only 15 out of 167 Rh immunized women had received anti-D immunoglobulin previously.

Conclusions: The incidence of Rh immunization has declined during the last 12 years possibly due to family planning and extensive use of anti-D immunoglobulin. However, complete eradication of Rh haemolytic disease of the newborn will be possible only if a comprehensive Rh prophylaxis programme is instituted.