MATERNAL ORIGIN OF NUCLEATED ERYTHROCYTES IN PERIPHERAL VENOUS-BLOOD OF PREGNANT-WOMEN

We studied the origin of nucleated red blood cells (NRBC) in periphera l venous blood samples from 40 pregnant women carrying a male fetus, u sing a technique that allows direct chromosomal analysis by in situ hy bridisation on immunologically and morphologically classified cells. S amples from ten nulligravid women were studied as controls. NRBC were enriched by negative magnetic activated cell sorting (mini MACS) using anti-CD45 monoclonal antibody. NRBC were detected by alkaline phospha tase anti-alkaline phosphatase immunostaining using a monoclonal anti- glycophorin A antibody. The origin of the NRBC was determined by fluor escence in situ hybridisation using X and Y specific probes. NRBC were found in 37 of the 40 pregnant women at a range of 1 to 230 per 20 ml of venous blood and in 6 of the 10 controls at a range of 1 to 3 per 20 ml of venous blood. All NRBC detected in the pregnant women were ev idently of maternal origin, and in the pregnant women the number of NR BC was significantly higher (P < 0.05) than in the controls. Pregnancy per se seems to induce the appearance of maternal NRBC in the circula tion, and it cannot therefore be assumed that NRBC isolated from the m aternal blood are of fetal origin on the basis of morphology alone. Di scrimination of fetal NRBC must occur for prenatal diagnosis of fetal genetic disorders.