The risk of Rhesus D alloimmunisation during or immediately after a first pregnancy is about 1%. Administration of 100 µg (500 IU) anti-D to women in their first pregnancy can reduce this risk to about 0.2% without, to date, any adverse effects. Although unlikely to confer benefit in the current pregnancy, fewer women may have Rhesus D antibodies in any subsequent pregnancy, but the effects of this needs to be tested in studies of robust design.
Multicentre trial of antepartum low-dose anti-D immunoglobulin.
Routine antenatal Rh immunoprophylaxis would substantially increase the use of anti-D Ig in the U.K. As availability of anti-D Ig is one factor influencing a decision to introduce routine antenatal prophylaxis, a trial was undertaken to test the efficacy of a lower dose of anti-D Ig than that used in earlier studies. RhD-negative primigravidae were randomized as controls or recipients of two doses of 250iu of anti-D Ig given at 28 and 34 weeks gestation. Blood samples were tested at delivery and at 6 months postpartum for the presence of immune anti-D, and again later if results were equivocal. Nine (1.5%) out of 595 control patients had immune anti-D at follow-up at 6 months and later; 4 (0.78%) of 513 treated women were immunized. It was concluded that, while two doses of 250iu of anti-D Ig may reduce alloimmunization, they are not as effective as two doses of 500iu in a previous trial.