A 24-chromosome FISH technique in preimplantation genetic diagnosis: validation of the method

Embryo screening for aneuploidy (AS) is part of preimplantation genetic diagnostics (PGD) and is aimed at improving the efficiency of assisted reproduction. Currently, several technologies, including the well-established fluorescence in situ hybridization (FISH) technique, cover the screening of all chromosomes in a single cell. This study evaluates a novel 24-chromosome FISH technique protocol (FISH-24). A total of 337 embryos were analyzed using the traditional 9-chromosome FISH technique (FISH-9) while 251 embryos were evaluated using the new FISH-24 technique. Embryos deemed nontransferable on Day 3 were cultured in vitro to Day 5 of development, then fixed and reanalyzed according to the technique allocated to each treatment cycle (107 embryos analyzed by FISH-9 and 111 by FISH-24). The global error rate (discrepancy between Day 3 and Day 5 results for a single embryo) was 2.8% after FISH-9 and 3.6% after FISH-24, with a p value of 0.95. Thus, we have established and validated a 24-chromosome FISH-based single cell aneuploidy screening technique, showing that the error rate obtained for FISH-24 is independent of the number of chromosomes analyzed and equivalent to the error rate observed for FISH-9, as a useful tool for chromosome segregation studies and clinical use.