Failure of anti-D immunoglobulin to remove fetal red cells from maternal circulation.

A Rhesus negative female was found post delivery to have circulating cells of fetal origin. The neonate was typed as D-positive. In spite of more than conventionally adequate doses of anti-D immunoglobulin given to the mother, the fetal cell count in the maternal circulation remained unchanged. Further investigation showed the fetus to be a Du variant and to exhibit a diminished reaction with the batch of anti-D immunoglobulin used.