Fetal cells in maternal blood

Fetal lymphocytes, trophoblasts, and nucleated red blood cells have each be en separated from maternal blood by methods such as flow cytometry, magneti c cell sorting, and charge flow separation. The frequency of fetal cells am ong circulating maternal mononuclear cells remains to be ascertained. Curre nt estimates range from about 10(-5) to 10(-7), but the numbers may be incr eased in women carrying aneuploid fetuses. Fetal cells separated from mater nal blood have been studied by methods such as polymerase chain reaction an d fluorescence in situ hybridization. Among fetal conditions so far identif ied are sex; human leukocyte antigen and Rh blood types; trisomy 13, 18 and 21; triploidy; and sickle cell anemia and thalassemia. Thus, fetal cell se paration might one day be used for screening of the common aneuploidies and , ultimately, for prenatal diagnosis. Individual fetal erythroid precursors have been cultured after separation in some laboratories. Culturing and ka ryotyping of separated fetal cells might enable diagnosis of a spectrum of chromosomal and genetic disorders. Further development will be required, ho wever, before regular clinical application of these methodologies.