Isolating fetal cells in the maternal circulation.

Fetal cells exist in maternal blood and can be utilized for prenatal genetic diagnosis. The use of polymerase chain reaction (PCR) technology on maternal blood has enabled the detection of fetal sex, Mendelian disorders (e.g. beta-globin mutations), 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 (FISH) with chromosome-specific DNA probes has allowed detection of trisomy 21, trisomy 18, Klinefelter syndrome (47,XXY) and 47,XYY. The fetal cell type that has generated the most success is the nucleated erythrocyte; however, trophoblasts, lymphocytes and granulocytes are also considered to be present in maternal blood. Fetal cells circulate in maternal blood during the first and second trimesters, with frequency increasing as gestation advances. Emphasis is thus now directed toward determining the most practical and efficacious manner for this technique to be applied to prenatal genetic diagnosis. A large scale collaboration of clinical evaluations is underway in the USA, upon completion of which assessment can be made of whether this technology can serve as an alternative to conventional invasive and non-invasive methods of prenatal cytogenetic diagnosis.