Small dose anti-Rh therapy after first trimester abortion.

The standard prophylactic dose of anti-Rh immunoglobulin used in the United States is 300 microgram. For use after spontaneous or induced abortion and diagnostic amniocentesis, this dose represents immunological "overkill". A 50 microgram dose has been effectively used for these patients in other countries but the specific products used were not equivalent to the products available in the USA. No evaluation of this 50 microgram dose has been conducted in the USA. This is a pilot study of 315 patients given a 50 microgram dose or a 300 microgram dose of anti-Rh immunoglobulin after first trimester abortion. No patient in either treatment group developed atypical blood group antibodies within 6 months. This finding confirms that 50 microgram of the American product is protective after first trimester abortion.