Anti-D administration in pregnancy for preventing rhesus alloimmunisation

Abstract

Background: A woman may develop Rh-negative antibodies during her first pregnancy when her fetus is Rh-positive. Antibodies develop most frequently after the 28th week of gestation.

Objectives: The objective of this review was to asses the effects of giving antenatal anti-D immunoglobulin at 28 weeks or more of pregnancy on the incidence of RhD alloimmunisation when given to Rhesus negative mothers without anti-D antibodies.

Search strategy: We searched the Cochrane Pregnancy and Childbirth Group trials register, Cochrane Controlled Trials Register, and bibliographies. Date of last search: December 1998.

Selection criteria: Randomised trials in Rhesus negative women without anti-D antibodies given anti-D after 28 weeks of pregnancy, compared with no treatment or placebo.

Data collection and analysis: Data were extracted by one reviewer and double entered.

Main results: Two eligible trials, which involved over 4500 women, compared anti-D prophylaxis with no treatment. Although the data suggested, when women receive anti-D at 28 and 34 weeks gestation, a reduced incidence of immunisation during pregnancy (0R O.44, 95% CI 0.18-1.12), after the birth of a Rhesus positive infant (OR 0.44, 95% CI 0.18-1.12), and within 12 months after birth of a Rhesus positive infant (OR 0.44, 95% CI 0.19-1.01), none of these differences were statistically significant. In the trial, which used the larger dose of anti-D (100ug; 500IU), there was a clear reduction in the incidence of immunisation at 2-12 months following birth in women who had received Anti-D at 28 and 34 weeks (OR 0.22 95% CI 0.05-0.88). No data were available for the risk of RhD alloimmunisation in a subsequent pregnancy. No differences were observed in the incidence of neonatal jaundice.

Reviewer's conclusions: The risk of RhD alloimmunisation during or immediately after a first pregnancy is about 1.5%. Administration of 100ug (500IU) anti-D at 28 weeks and 34 weeks gestation to women in their first pregnancy can reduce this risk to about 0.2% without, to date, any adverse effects. Although such a policy is unlikely to confer benefit or improve outcome in the present pregnancy, fewer women will have Rhesus D antibodies in their next pregnancy. Adoption of such a policy will need to consider the costs of prophylaxis against the costs of care for women who become sensitised and their affected infants, and local adequacy of supply of anti-D gammaglobulin.