Problems in prenatal diagnosis resulting from chromosomal mosaicism

Prenatal diagnosis was performed on a 36‐year‐old woman with a history of Tay‐Sachs disease in one of her children. A diagnosis of 45, X was made by conventional karyotype analysis on the first amniotic fluid specimen. Cells from this specimen also showed a small fluorescent body, leading to suspicion of the presence of a Y chromosome. Special staining techniques demonstrated a possible D/Y translocation. The patient elected to have a therapeutic abortion and a male fetus was expelled. Subsequent culture of the amniotic fluid obtained at the time of abortion revealed 46,XY. The indications for prenatal cytogenetic diagnosis, the problems of diagnosing in utero mosaicism, and the problems resulting from the application of new methods of chromosome identification are discussed.