RESUMEN
The aim of the study was to prospectively evaluate the usefulness and limitations of Fluorescence In Situ Hybridization (FISH) on uncultured cells for prenatal diagnosis of numeric aneuploidies of chromosomes 13, 18, 21, X and Y. Hundred prospectively selected pregnant women that were at high risk of giving birth to an abnormal child were offered prenatal diagnosis by FISH after appropriate counseling. Fetal tissue was obtained by chorionic villus sampling (n=26), amniocentesis (n=62) and or fetal blood sampling (n=12) and processed for FISH using commercial probes. Six cases were excluded initially owing to maternal blood contamination or inadequate sample. FISH results were available in 98% of cases, in 2% of cases there was FISH failure. Of the remaining 92 cases, chromosome aneuploidy was detected in eleven cases. FISH was found extremely valuable in cases presenting with fetal abnormalities detected on ultrasonography and also for rapid screening of aneuploidies in cases of abnormal triple marker test. But as the diagnosis is limited to only a small number of chromosomes, appropriate evaluation of the cases with counseling regarding the limitations of FISH is mandatory before offering this test for prenatal diagnosis.