[Significance of chromosomal mosaicism diagnosed by amniocentesis]

Second-trimester amniocentesis, performed in a 39-year-old woman, revealed on two different taps a weak aneuploid cell line 47,XY+C or X (2 clones), with a strong majority of fetal cells being 46,XY normal (15 clones). A chromosome examination carried out on cord blood after the birth of a phenotypically normal infant confirmed the presence of mosaicism, with 12% of the cells being 47,XXY. The authors consider the manner in which mosaicism diagnosed by amniocentesis may be interpreted, pointing out the danger of hasty conclusions in this domain, which has not yet been adequately explored.