Anti-D: Does Method of Administration Make a Difference?

Intramuscular anti-D and intravenous anti-D administered in the 28th week of pregnancy are equally effective for the prevention of Rhesus alloimmunization during pregnancy, according to a new intervention review conducted by the Cochrane Pregnancy and Childbirth Group.¹
   
Antibodies to the red blood cell Rhesus D (RhD) antigen may form in an RhD-negative mother if blood from an RhD-positive fetus enters the mother’s circulatory system at birth or during a procedure, such as an amniocentesis. This sensitization to Rh factor, or RhD alloimmunization, generally occurs spontaneously between 28 weeks’ and 30 weeks’ gestation. Once maternal antibodies to Rh factor have developed, these maternal antibodies can attack fetal erythrocytes, which can cause hemolytic disease in the baby, including anemia, edema, jaundice and, rarely, death. RhD alloimmunization that occurs in the first pregnancy generally does not harm the baby. However, subsequent pregnancies are at risk for Rh disease if this condition is undetected or untreated.
   
The administration of Rh immunoglobulin can prevent sensitization in 99.8% of women, but the treatment is ineffective if sensitization has already occurred.² To prevent future sensitization in Rh-negative women, anti-D must be administered during subsequent pregnancies and when a miscarriage, abortion, or ectopic pregnancy occurs.
   
To determine whether there are any differences in the effectiveness of anti-D IgG related to route of administration, researchers analyzed the results of relevant 2 studies. One study was small, involving just 14 women, and the other study had 432 participants. All 447 women were Rh-negative, and both studies compared intramuscular and intravenous administration of anti-D prophylaxis with 1500 IU (300 micrograms) of Rhophylac at 28 weeks’ gestation. There were no cases of sensitization reported in either study.
   
The only difference noted was that one study reported that the anti-D IgG concentration (mean ± SD) on day 7 post-treatment was higher in the intravenous group than in the intramuscular group (36.1 ± 2.6 ng/mL vs 19.8 ± 8.7 ng/mL, respectively). After 2 to 3 weeks post-treatment, however, the mean anti-D IgG concentrations were similar for both routes of administration. Based on these findings, the researchers concluded that the method by which anti-D is administered has no affect on the efficacy of anti-D in the prevention of RhD antibody formation during pregnancy.

Pertinent Points:
- Anti-D is equally effective in preventing RhD antibody formation in Rh-negative women when administered intravenously or intramuscularly.
- The route of administration of anti-D should depend on preparation availability, the required dose needed, and patient preference.