Blastocyst transfer after aseptic vitrification of zygotes: an approach to overcome an impaired uterine environment

In some IVF cycles, no fresh embryo transfer in the stimulated cycle is advisable. The cryopreservation of zygotes and the transfer of blastocysts in a cryo-embryo transfer is an option to circumvent an inadequate uterine environment due to risk of ovarian hyperstimulation syndrome, inappropriate endometrium build up, endometrial polyps or uterine myomas. For this strategy, highly secure and safe cryopreservation protocols are advisable. This study describes a protocol for aseptic vitrification of zygotes that results in high survival rates and minimizes the potential risk of contamination in liquid nitrogen during cooling and long-term storage. In mouse zygotes, there was no difference in efficiency as compared with a conventional open vitrification system. In IVF patients, aseptically vitrified zygotes showed no difference in blastocyst formation rate as compared with sibling zygotes kept in fresh culture. A clinical study comprising 173 cryo-cycles with a transfer of blastocysts originating from vitrified zygotes showed an ongoing pregnancy rate of 40.9%. The live birth rate per patient was 36.8%. A combination of good clinical results and increased safety conditions due to aseptic vitrification encourages the use of cryo-embryo transfer for patients with a suboptimal uterine environment in a fresh cycle

The Evolution of the Cryopreservation Techniques in Reproductive Medicine - Exploring the Character of the Vitrified State Intra- and Extracellularly to Better Understand Cell Survival after Cryopreservation

peer reviewedNowadays, cryopreservation of gametes and embryos is a fundamental, integral and indispensable part of infertility treatment or fertility preservation. Cryopreservation is not only needed for the policy of single embryo transfer and cryopreservation of surplus embryos but for deferring embryo transfer in case of ovarian hyperstimulation syndrome (OHSS), uterine pathologies and suboptimal endometrium built-up or when preimplantation genetic testing is needed. Several current strategies in ART would be inconceivable without highly efficient cryopreservation protocols. Nevertheless, cryopreservation hampered for a long time especially in terms of low survival rates after freezing and thawing. Only the technical progresses during the last decades, namely in regard to the implementation and advancement of vitrification leveraged its application and, thus, even allows the cryopreservation of human oocytes – a process which is far from being easy. This review aims to provide a deeper insight into the physical processes of cryopreservation and to explore the character of the vitrified state in the extra and intracellular milieu in order to demonstrate that the common denominator to all cryopreservation procedures is the establishment of an intracellular amorphous condition that hinder the likelihood of crystallization