Prenatal detection of fetal Down's syndrome from maternal plasma.

Fetal DNA is present in maternal plasma, and a proportion of such DNA is seen in intact fetal cells. We investigated the use of fluorescence in-situ hybridisation (FISH) techniques on maternal plasma samples. In plasma samples obtained from three women carrying fetuses affected by trisomy 21 (Down's syndrome), we identified fetal cells with three chromosome-21 signals. These results show the feasibility of non-invasive detection of fetal chromosomal aneuploidy by maternal plasma analysis.