Efficiency of aseptic open vitrification and hermetical cryostorage of human oocytes

The present study reports, as far as is known for the first time, the safety of UV sterilization of liquid nitrogen and hermetical cryostorage of human oocytes by comparing the efficiency of fresh and vitrified sibling oocytes of infertile patients. A prospective randomized study on sibling oocytes of 31 patients was carried out. Metaphase-II oocytes were randomized for intracytoplasmic sperm injection and the supernumerary sibling oocytes were vitrified using a novel Cryotop aseptic procedure (UV liquid nitrogen sterilization and hermetical cryostorage). After unsuccessful attempts with fresh oocytes, vitrified sibling oocytes were injected. Mean outcome measures observed were fertilization, cleavage and top-quality embryo rates. No significant differences were observed between the fresh and vitrified-warmed sibling oocytes: oocyte fertilization was 88.3% versus 84.9%; cleavage 72.6% versus 71.0%; top-quality embryos 33.8% versus 26.3% and mean number of transferred embryos 2.6 ± 0.1 versus 2.5 ± 0.1, respectively. Clinical pregnancy rate per cycle with vitrified-warmed oocytes was 35.5% (implantation rate 17.1%) and seven healthy babies were born. This study demonstrated that UV liquid nitrogen sterilization and hermetical cryostorage does not adversely affect the developmental competence of vitrified oocytes, allowing safe aseptic open vitrification applicable under strict directives on tissue manipulation.