A major goal in prenatal diagnosis is to develop non-invasive techniques that do not endanger the fetus. One such approach would be to isolate fetal cells from the maternal circulation. The fetal cell type that has generated the most success is the nucleated erythrocyte; however, trophoblasts, lymphocytes and granulocytes are also present in maternal blood. Polymerase chain reaction technology has enabled the detection of fetal sex, Mendelian disorders (e.g. β-globin motations), HLA polymorphisms, and fetal Rhesus (D) blood type. Enrichment for erythroblasts and trophoblasts by various density gradient and flow sorting techniques followed by fluorescence in situ hybridization with chromosome-specific DNA probes has allowed detection of trisomy 21, trisomy 18, and Klinefelter syndrome (47, XXY) and 47, XYY. To assess whether this technology can serve as an alternative to conventional invasive methods of prenatal cytogenetic diagnosis, a United States collaborative clinical investigation has recently begun.
