CHARGE FLOW SEPARATION - QUANTIFICATION OF NUCLEATED RED-BLOOD-CELLS IN MATERNAL BLOOD DURING PREGNANCY

We set out to ascertain the numbers of fetal cells that enter the mate rnal blood stream during pregnancy. Samples of 15-16 mi of whole blood were collected from 225 women-mostly 10-18 weeks pregnant-and then pr ocessed by charge flow separation, a novel method based on free flow e lectrophoresis in a buffer counterflow gradient. After their recovery in four different separation instruments, nucleated red blood cells (N RBC) were enumerated histologically. In some cases fetal NRBC were ide ntified and enumerated by fluorescence in situ hybridization with prob es for the X and Y chromosomes and fetal haemoglobin mRNA. Recoveries were consistent among the four separation instruments: the median numb ers of NRBC obtained were 4190, 1590, 2805 and 3860. Our data show tha t approximately 30 per cent of those cells were fetal. Thus, recent re ports on the separation of fetal NRBC by other methods, give underesti mates of their frequency in maternal blood. (C) 1998 John Wiley & Sons , Ltd.