Detection of fetal erythrocytes in maternal blood post partum with the fluorescence-activated cell sorter

A study was made of the frequency and amount of fetal hemorrhage into maternal blood during labor and delivery as evidenced by the number of fetal cells present in the maternal circulation immediately after spontaneous vaginal delivery. A sensitive, indirect immunofluorescence was used with fluorescence-activated cell sorter analysis of erythrocytes. All of the 16 Rh-negative mothers studied after vaginal delivery of Rh-positive infants had circulating Rh-positive cells. The mean Rh-positive to Rh-negative erythrocyte ratio was 1:14,100 in maternal blood, which corresponds to a mean fetal hemorrhage of 156 µl. The test described is sufficiently sensitive to be used for the study of primary Rh isoimmunization and could be clinically applicable for antepartum screening to determine which patients require Rh immune globulin treatment before delivery.