Anti-D administration in early pregnancy - time for a new protocol

The use of anti-D immunoglobulin has dramatically reduced the incidence of rhesus isoimmunization arising from pregnancy. A critical shortage of anti-D has developed and consumption must be reduced, preferably without increasing the risk of isoimmunization. The standard dosage of anti-D currently given at all gestational ages is 1 ampoule containing 125 micrograms of anti-D. Of the anti-D administered half is during the first trimester when a much lower dose could be used; 30 micrograms would remove from the maternal circulation the entire fetoplacental blood volume (3 ml) of a 12 week's pregnancy. A dose of 30 micrograms would also be adequate for most fetomaternal transfusions after 12 weeks but prior to the third trimester. A larger dose could be administered if maternal Kleihauer testing suggests the need for a supplementary dose. In the third trimester, the current regimen is appropriate - a dose of 125 micrograms of anti-D supplemented when needed on the basis of maternal Kleihauer testing. A lower dose ampoule of anti-D should be available. In addition, existing protocols for anti-D administration should be modified so that smaller more appropriate doses are given, better utilizing the limited supply of anti-D.