Introduction. The maximum efficiency was shown when transferring expanded blastocysts on Day 5, but 30% of embryos show developmental delays and reach the desired stage at Day 6. In the absence of an expanded blastocyst by Day 5 of development, there are two possible options: cultivate embryos up to Day 6 with the purpose of transfer or cryopreservation. Objective — to evaluate pregnancy rate (PR) in IVF cycles with transferring embryos on Day 6 in native or cryocycles, as well as evaluation PR in cryocycles with transferring blastocysts frozen on Day 6 or Day 5. Material and methods. 2169 IVF program results were analyzed to measure pregnancy rate on Day 6 embryo transfer (109 patients) or Day 5. In addition, a comparison of the effectiveness of native programs and cryocycles was done. In 71 (65%) patients embryo cryopreservation was performed on Day 6, in 38 — embryo transfer was carried out. Results. The results show the worst results in the case of embryo transfer on Day 6 (PR — 32%, Day 5 — 45%), in particular, if there is one embryo per transfer (23%). In the case of embryo transfer in the cryocycle the program’s effectiveness rises to 37%. The results of cryocycles using embryos on Day 5 or Day 6 are not significantly different (45 and 37%, respectively). PR when transferring embryos in native cycles indicates that the slow development of the embryo reduce the likelihood of successful implantation. In cryocycles PR has no statistical differences when transferring Day 6 or Day 5 of embryo development. In the absence of the ability to transfer embryos in native cycle on Day 5 (the absence of embryos at the stage of the expanded blastocyst) it is better to cultivate them up to Day 6 with subsequent cryopreservation. The day of embryo transfer is an important predictor of clinical outcomes.