Chromosomal mosaicism in chorionic villus sampling.

The observation of multiple, chromosomally distinct cell lines in chorionic villus samples is not an unusual finding and occurs in 1 per 100 samples. This frequency is ten times greater than the level of mosaicism observed in newborn surveys and, thus, must reflect phenomenon other than true fetal mosaicism. Indeed, only 23% of mosaicism detected at CVS is confirmed in the fetus (2.