Transplacental passage of fetal red cells in abortion; increased incidence after curettage and effect of oxytocic drugs.

In a study of early abortions (less than 16-week pregnancies) no significant increase in fetomaternal haemorrhage was found in patients having either threatened or incomplete abortions. A statistically significant increase in fetal cells in the maternal circulation, however, occurred after curettage. The administration of oxytocic drugs in conjunction with curettage in cases of incomplete abortion did not increase the incidence of transplacental passage of fetal erythrocytes when compared with curettage alone. Of the 81 patients curetted following abortion four had a feto-maternal haemorrhage of more than 0.2 ml. The largest amount of fetal blood found in the maternal circulation was 0.4 to 0.5 ml. Preliminary data evaluating the indirect Coombs test and enzyme-treated red cells in Rh-negative post-abortion cases suggest that this amount of blood is not a primary immunizing dose but a "booster" to preformed antibody.