Prenatal detection of trisomy 21 in uncultured amniocytes by fluorescence in situ hybridization: a prospective study

A prospective study was undertaken to evaluate the use of fluorescence in situ hybridization (FISH) for the detection of trisomy 21 in interphase nuclei of uncultured amniotic fluid cells. Five hundred cases were analysed in situ and classified as normal or abnormal; the results were subsequently checked against the cytogenetic findings. Four hundred and ninety-three were correctly identified as normal with an 86.6 per cent average frequency of scored nuclei exhibiting two signals; six cases were correctly identified as trisomic for chromosome 21 with 81.7 per cent of scored nuclei exhibiting three signals; and one abnormal case involving an unbalanced chromosome 21:21 translocation was falsely scored as normal due to poor hybridization/detection efficiency. The method has been substantially improved and simplified so that it is suitable for the rapid detection of trisomy 21. As aneuploidy detection in interphase does not identify structural chromosome aberrations, it is not a substitute for fetal chromosome analysis.