Chromosomal mosaicism in amniotic cell culture: a diagnostic dilemma

Chromosomal mosaicism, with supernumerary C or D group elements, was observed in the cultured amniotic fluid cells of four fetuses undergoing prenatal diagnosis. There were discrepancies in the karyotypes of cells from different culture flasks of a single fluid sample, between cultures from successive uterine aspirations, and between cultures of amniotic fluid and fetal tissues obtained by pregnancy interruption. Most alarming was the finding, in one case, of identical mosaicism in different culture flasks as well as in repeated amniocenteses derived from a phenotypically normal fetus. In each instance, the aborted fetus or newborn infant proved to be phenotypically and cytogenetically normal. This suggests that mosaicism, demonstrated in cultured amniotic fluid cells, may not reflect the chromosomal constitution of the fetus and may pose a dilemma regarding an accurate diagnosis.