Red blood cell iso-immunisation in the Wellington area of New Zealand: the case for antenatal prophylaxis.

The present study aimed to calculate the rate of Rhesus D iso-immunisation during pregnancy in Wellington, New Zealand and to identify the timing of iso-immunisation. The notes of all women and their babies with positive antenatal anti-D antibody screens during the period 1994-2002 at the regional reference laboratory (Wellington Blood Transfusion Service) were reviewed to identify the antibody titre and the stage of pregnancy that the antibodies developed. Twelve percent of all tested pregnant women were Rhesus D negative and the annual immunisation rate during pregnancy was 1.4%. Sensitisation during the third trimester occurred in 50% of these women. Sensitisation in the third trimester was more common in primigravid women (87%) than in multiparous women (27%).