The fetal erythroblast is not the optimal target for non-invasive prenatal diagnosis: preliminary results.

Fetal cells, present in the blood of pregnant women, are potential targets for non-invasive prenatal diagnosis. The fetal erythroblast has been the favorite target cell type. We investigated four methods of enrichment for fetal erythroblasts, identifying only three fetal erythroblasts in 573 ml of maternal blood. This is much less than the expected two to six fetal cells per ml of maternal blood. Hamada and Krabchi used a cell type-independent marker, i.e., the Y chromosome in maternal blood from male pregnancies after Carnoy fixation, leaving the nuclei for hybridization with X-and Y-chromosome-specific probes. We found with a similar technique 28 fetal cells in 15 ml of maternal blood. The fetal origin of cells was confirmed by hybridizing the nuclei with X- and Y-chromosome-specific probes, using two consecutive hybridizations with the two probes in opposite colors (reverse FISH). Candidate fetal cells were inspected after each hybridization. Only cells that were found to change the color of both probe signals from first to second hybridization were diagnosed as fetal. To reduce the labor-intensive slide screening load, we used semiautomated scanning microscopy to search for candidate cells. We conclude that erythroblasts form only a small fraction of fetal cells present in maternal blood.