Prenatal diagnosis of fetal chromosome abnormalities currently relies on invasive testing, by amniocentesis or chorionic villous sampling in women considered to be at high risk. Evaluation of high-risk pregnancies includes a positive result for a screening test. Because of the uncertainties of screening and invasive procedure related risk, as well as miscarriage and maternal medical complications, there is a considerable interest in developing noninvasive alternatives for obtaining genetic information of the gestating fetus. One such alternatives involves recovery of fetal cells from maternal circulation.

The presence of fetal cells was, at first, probably reported in 1893, when fetal trophoblasts were found in the lung of a pregnant woman affected by eclampsia, a severe disease of the pregnancy. In 1969, Y-chromatin was reported in blood cells from women carrying male fetuses. Ten years later, fetal leukocytes were detected and, in 1990, fetal nucleated red blood cells were recovered. In summary...