Fluorescent-in-situ-hybridization allows rapid prenatal detection of fetal aneuploidies within few hours

Last years evaluation of fluorescence-in-situ-hybridization (FISH) allowed detection of chromosomal abnormalities by using DNA probes, binding to chromosomes in the nucleus. Because it is possible to directly examine interphase nuclei, FISH-technique, in contrast to traditional cytogenetic analysis has the advantage of small loss of time in case of urgent decisions on perinatal management. Karyotyping was performed on fetal cells, obtained from 72 pregnancies after amniocentesis, by both classical cytogenetics and fluorescence in situ hybridization using commercially available kits which utilise the alpha satellite probes for chromosomes 13+21 and 18. The classical cytogenetics demonstrated that the fetal karyotype was normal in 67 cases and abnormal in 5 cases (four with trisomy 21 and one with a translocation trisomy 18). With the FISH-technique it was possible to obtain accurate diagnosis of trisomy 21 within 24 hours of sampling. The distribution of the number of signals in the chromosomally normal and abnormal fetuses was significantly different, but we were not able to identify the fetus with translocation trisomy 18. We conclude that in the investigation of fetuses with ultrasonographic diagnosed malformations, FISH provides a rapid technique for detection of numerical chromosomal aberrations, but replacement of classical cytogenetics is not possible because of its limitations for identification of subtle structural chromosomal abnormalities.