Prenatal diagnosis of chromosomal aneuploidies by fluorescence in situ hybridization on uncultured amniotic cells: experience with 630 samples.

612 amniotic fluid samples have been analyzed by an interphase FISH protocol in order to identify the X, Y, 13, 18 and 21 chromosomes in uncultured amniotic cells, parallel to conventional cytogenetic techniques. The aims were to value the interest and the feasibility of such technique in a regional prenatal diagnosis laboratory, and to estimate the assistance FISH can give in cases of supposed fetal mosaics and the importance of the reservations voiced by certain teams about FISH use when the fluid is hemorrhagic or about the employment of certain probes. The ten aneuploidies of the set, seven autosomal and three gonosomal, have been perfectly identified. Only one misdiagnosis has been reported, which clearly show the FISH limits: it was derived from a morphological rehandling in a chromosomal segment labeled by a probe. Regarding to the mosaics, the respective numbers of each cellular populations estimated by interphase FISH seems not to differ from those valued by the metaphase cytogenetic. Finally our results in hemorrhagic samples (64/612) seem not different than those obtained with clear samples.