Chromosomal mosaicism in chorionic villus sampling

Chromosomal mosaicism, the presence of more than one karyotypically distinct cell line, is detected in about 1% of chorionic villus samples. The multiple cell lines observed can result from several different phenomenon including true mosaicism in the fetus, pseudomosaicism in culture, confined placental mosaicism, maternal cell contamination or chimerism. Most of the discrepant results reported in chorionic villus sampling are due to the occurrence of confined placental mosaicism. The observation of mosaicism in chorionic villus samples can complicate the interpretation of prenatal results and presents unique problems in genetic counseling. It does not, however, appear to be associated with an adverse outcome for the fetus.