Objective: Information on preimplantation diagnostics (PGD) by means of the method of fluorescent in situ hybridization (FISH) and some factors, which principally influence the results obtained with this technique from the point of view of a molecular cytogeneticist. Critical steps of work with one cell in PGD-FISH are summarized based on data from literature as well as from the authors, own experimental experience. The individual steps are analyzed and possibilities of execution are presented. Type of study: A review. Setting: Institute of Medical Genetics and Fetal Medicine of Faculty Hospital and Medical Faculty of Palacky University, Center of Assisted Reproduction at Obstetric-Gynecological Clinic, Faculty Hospital, Olomouc. Subject and Methods of Study: Introduction into the PGD problem. A survey and analysis of factors decisive for the success of the FISH method for PGD. – Selection of embrya for the experimental phase of PGD-FISH. – Selection of fixation method and pretreatment, application of suitable probes. – Localization of the fixed cell. – Interpretation of the results obtained. Recommendation of the mode of their successful solution. Conclusion: The paper presents a survey of the PGD-FISH method. Some critical aspects in the analysis of unicellular preparation are pointed out and evaluated and possibilities and procedures of the optimal solution are suggested.

        Key words: preimplantation genetic diagnostics, PGD, FISH, IVF, aneuploidia