Background and Aim: Prenatal diagnosis of chromosome abnormalities is usually performed on amniotic fluid samples. Aneuploidy screening by fluorescence in situ hybridization (FISH), although not an alternative for conventional cytogenetics, has become a useful tool. Materials and Methods: We compared the results of FISH and conventional cytogenetic analysis applied on 51 amniotic fluid samples between January 2002 and December 2005, in our Cytogenetics Laboratory. Amniocytes were extracted using 5 cc of the sample, and direct FISH was applied using an AneuVysion Assay Kit (Vysis). The remaining fluid samples were used for chromosome analysis by conventional methods after long-term cell cultures. Results: The results of both methods were compatible for 48 patients. For the 2 patients, although FISH results were normal, structural abnormalities were detected by the conventional cytogenetic method. In one patient, we detected mosaic trisomy 21 by FISH, whereas a 47,XX,+21 karyotype was identified in all cells that were examined by the conventional cytogenetic method. Conclusions: During genetic counseling, it is important to inform patients who undergo aneuploidy screening by FISH about the advantages and disadvantages of the method to help them acknowledge the results in the event that an abnormality is identified in the karyotype.

Background and Aim: Prenatal diagnosis of chromosome abnormalities is usually performed on amniotic fluid samples. Aneuploidy screening by fluorescence in situ hybridization (FISH), although not an alternative for conventional cytogenetics, has become a useful tool. Materials and Methods: We compared the results of FISH and conventional cytogenetic analysis applied on 51 amniotic fluid samples between January 2002 and December 2005, in our Cytogenetics Laboratory. Amniocytes were extracted using 5 cc of the sample, and direct FISH was applied using an AneuVysion Assay Kit (Vysis). The remaining fluid samples were used for chromosome analysis by conventional methods after long-term cell cultures. Results: The results of both methods were compatible for 48 patients. For the 2 patients, although FISH results were normal, structural abnormalities were detected by the conventional cytogenetic method. In one patient, we detected mosaic trisomy 21 by FISH, whereas a 47,XX,+21 karyotype was identified in all cells that were examined by the conventional cytogenetic method. Conclusions: During genetic counseling, it is important to inform patients who undergo aneuploidy screening by FISH about the advantages and disadvantages of the method to help them acknowledge the results in the event that an abnormality is identified in the karyotype.