Currently in the clinics of assisted reproductive technologies (ART) embryos are transferred at the stage of blastocysts on the 5th and 6th day of development. This corresponds to physiological norms. It is known fact that blastocysts undergo radical morphological reconstructions on the 5th and 6th day of development. It is important to understand the embryo of which day is better implanted into the uterus - before or after reconstruction. Using statistical analysis, based on data about 4130 patients, a comparison of the probability of successful ART result between embryos of 5th and 6th day, obtained by fertilization of pre-cryopreserved oocyte was made. Three age groups and groups of patients with transferred embryos of different quality and degree of development (according to D. Gardner) were studied. It was found that the relationship between the day of embryo development and the probability of positive outcome of assisted reproductive technologies (ART) exists. A large selection size made it possible to obtain results with a high asymptotic accuracy p = 0.005. From obtained data, it can be seen that clinical pregnancy occurs more often if the transferred embryos develop to the stage of the blastocyst faster, i.e. on the 5th day. In addition, the analysis allows to draw conclusions related to the overall results of ART programs.
embryo of 5th day, blastocyst, ART
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