Fetal nucleated red blood cells from CVS washings: an aid to development of first trimester non-invasive prenatal diagnosis

Fetal nucleated red blood cells (n-rbc) occur in the maternal circulation f rom 7 weeks of pregnancy. The enrichment of these cells from maternal blood will depend upon their stage of differentiation, which changes during deve lopment. We characterised the fetal n-rbc from chorionic villus sample (CVS ) washings and used them to model first trimester non-invasive prenatal dia gnosis. The ratio of epsilon- to gamma -globin-producing cells declined rap idly from 10 to 13 weeks, as did the ratio of nucleated to non-nucleated rb c. By 13 weeks the great majority of cells containing gamma- or epsilon -gl obin are anucleate. The fetal n-rbc were highly variable in size and densit y and sedimented over a wide density range with a high proportion (>80%) at a density overlapping with that of maternal rbc. We have devised an enrich ment procedure using Orskoff lysis to differentially lyre the maternal cell s followed by density centrifugation and separation using magnetic beads. T his simple protocol allowed recovery of 70% (69 +/- 22%) of fetal cells whe n added at approximately 10 fetal cells/ml maternal blood. When 1 fetal cel l/ml millilitre maternal blood was added (total volume 10 ml) the recovery was more variable but remained at approximately 70% (72 +/- 47%), with at l east one fetal cell recovered in all cases. Copyright (C) 2001 John Wiley & Sons, Ltd.