Fetal cells in the maternal circulation.

The analysis of fetal cells from the maternal circulation would be the least invasive method of prenatal diagnosis. Potential fetal cell types to enter the maternal circulation are lymphocytes, trophoblast cells and nucleated erythrocytes. With conventional methods, such as cytology and interphase or metaphase cytogenetics, the ratio of fetal to maternal cells was overestimated in the past. Currently most groups use polymerase chain reaction-based Y-sequence analysis for the detection of fetal cells in pregnancies with male fetuses, either with or without prior enrichment of fetal cells. For fetal cell separation, fluorescence-activated cell sorting and immunomagnetic beads have been applied, and recently our group has used discontinuous density gradient centrifugation for this purpose. We have shown that the transferrin receptor antigen alone is not sufficient for enrichment of fetal nucleated erythrocytes. Despite some initial promising results with fluorescence in situ hybridization, the reproducibility and reliability of the techniques are still limited, mainly due to the lack of very specific cell markers and the very low and variable concentrations of fetal cells among numerous maternal cells.