Tips and Tricks in Fluorescence In-situ Hybridization (FISH)- based Preimplantation Genetic Diagnosis /Screening (PGD/PGS)

As numerical and structural defects in chromosomes are an inevitable consequence of IVF, Pre-implantation genetic diagnosis and screening (PGD/PGS) methods are used for detecting abnormalities in embryos before implantation to the uterus to increase the successful rate of IVF. Pre-implantation genetic diagnosis and screening approaches can be achieved by different techniques such as NGS, CGH and FISH. Among these approaches, FISH-based PGD/PGS is challenging in that it requires experience and skill to increase its facility and validity. Therefore, based on literature review and our experiences obtained from genetic laboratory of Yazd Reproductive Sciences Institute (Yazd, Iran), we were ditermined to discuss these challenges. After reviewing the available protocols and articles, we compared results of different methods for performing pre- and post-examination FISH process. Required samples in each section were obtained from embryo in cleavage or blastocyst stage. According to our team's experience, we recommend the cleavage stage biopsy and our modified fixation method. Also, we do not recommend more than two round hybridization on the same cell. Many studies have shown that FISH-based PGD is an efficient method for decreasing IVF failure in infertile patients. This paper introduces the best biopsy and fixation method and, includes some useful tips and tricks on type and number of probe, removing the cytoplasm, denaturation and hybridization, data evaluation and scoring criteria.