Development of cryopreservation methods for gametes and embryos is closely related to ART programs. Since the beginning of embryo and gamete banking in 1972, it has been possible to preserve embryos not used for transfer, and to develop programs for fertility preservation and biological material donation. After applying the cryopreservation procedure, more than a million of children were born in the world, and the protocols currently used have proven their safety, since the health of these children does not differ from the general population.
Vitrification is the achievement of a glass–like state without formation of crystals during ultrafast cooling. In contrast to the previously common methods of slow controlled freezing, in which formation of ice crystals and possible death of the embryo were inevitable, thanks to vitrification we are able to achieve very fast cooling rates of the sample (about 20,000 ° C/min) and its transition to an amorphous glass-like state. Therefore, vitrification method is practically harmless to cells, which makes it possible to restore their vitality after thawing with the highest probability and to achieve more than 99% survival for embryos after cryopreservation. In cryobank, the material is stored at very low temperatures of liquid nitrogen (-196 ° C), which makes it possible to completely stop all biochemical processes in cells, and the duration of such storage is practically unlimited.
Vitrification is so safe that it is possible to cryopreservate embryos without undue fear if the embryo transfer is currently impossible: in case of threat of hyperstimulation syndrome, endometrium incompetence at the time of proposed transfer, as well as during preimplantation genetic testing. In addition, with vitrification, it is possible to cryopreservate an embryo several times, which makes it possible to perform PGT on embryos that have not been previously analyzed.
Oocytes are the most sensitive to cryopreservation, since they are significantly larger than individual cells of the embryo at the cleavage stage or blastocysts, and division spindle is also sensitive to the freezing process. According to the Alpha international consensus, in slow freezing protocols, only 50% of oocytes retained their ability to fertilize after thawing. With vitrification, this indicator was increased to 85-95%, so this method is the only way to store them effectively and it is performed in our clinic in programs of delayed maternity, banking of donor oocytes and fertility preservation in cancer patients.