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

Abstract

Fetal nucleated red blood cells (n-rbc) occur in the maternal circulation from 7 weeks of pregnancy. The enrichment of these cells from maternal blood will depend upon their stage of differentiation, which changes during development. We characterised the fetal n-rbc from chorionic villus sample (CVS) washings and used them to model first trimester non-invasive prenatal diagnosis. The ratio of epsilon- to gamma-globin-producing cells declined rapidly from 10 to 13 weeks, as did the ratio of nucleated to non-nucleated rbc. By 13 weeks the great majority of cells containing gamma- or epsilon-globin are anucleate. The fetal n-rbc were highly variable in size and density 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 enrichment procedure using Orskoff lysis to differentially lyse the maternal cells followed by density centrifugation and separation using magnetic beads. This simple protocol allowed recovery of 70% (69+/-22%) of fetal cells when added at approximately 10 fetal cells/ml maternal blood. When 1 fetal cell/ml millilitre maternal blood was added (total volume 10 ml) the recovery was more variable but remained at approximately 70% (72+/-47%), with at least one fetal cell recovered in all cases.