THE PROPORTION OF FETAL NUCLEATED RED-BLOOD-CELLS IN MATERNAL BLOOD -ESTIMATION BY FACS ANALYSIS

The purpose of this study was to determine the proportion of fetal nuc leated red blood cells (NRBCs) among enriched NRBCs and to evaluate th e effectiveness of enriching NRBCs in maternal blood using fluorescenc e-activated cell sorting (FACS) to separate NRBCs. The origin of enric hed NRBCs was determined using fluorescence in situ hybridization (FIS H) methods. Y-specific signals were observed in 4.6 +/- 1.5 per cent o f the enriched cells from 14 of 16 (87.5 per cent) pregnant women who gave birth to boys. In this series, the specificity of the fetal sex d iagnosis was 100 per cent, the sensitivity 88 per cent, and the negati ve predictive value 86 per cent. Fetal NRBCs are present in maternal b lood and FACS has the potential to enrich fetal NRBCs. Fetal cells wer e estimated to be enriched more than 10 000-fold in the first trimeste r and more than 100-fold in the third trimester. Average frequencies o f fetal cells in maternal blood were 8.1 x 10(-5) and 1.6 x 10(-5) in the first trimester and the second/third trimesters. However, most of the NRBCs in maternal blood are maternal in origin. (C) 1997 by John W iley & Sons, Ltd.