The isolation and analysis of nucleated fetal cells (NFCs) from maternal blood 
may represent a new approach to noninvasive prenatal diagnosis. Although 
promising, these techniques require highly accurate separation of NFCs from 
nucleated cells of maternal origin; the two major problems limiting these 
techniques are the relative rarity of fetal cells in maternal blood and the need 
to establish their fetal origin. We now report a novel procedure that has 
allowed accurate separation of NFCs from maternal cells. The technique reported 
involves direct micromanipulator isolation of histochemically identified 
hemoglobin F-positive nucleated cells to obtain fetal nucleated red blood cells 
(FNRBCs) of high yield and purity. Using this technique, followed by 
cell-by-cell multicolor fluorescence in situ hybridization (FISH) analysis of 
purified FNRBCs, we were able to detect some of the most common human 
aneuploidies (including Down syndrome, Klinefelter syndrome, and trisomy 13) in 
33 pregnant women referred for amniocentesis. The procedure used, which can be 
completed in <72 hrs, produced complete concordance with the results of 
amniocentesis. We also confirm findings of prior studies suggesting that the 
number of FNRBCs in maternal circulation is remarkably higher in abnormal 
pregnancies than in normal pregnancies, especially in women carrying a fetus 
with trisomy 21.