Effect of Vitrification and Warming Media on Pregnancy Rates in the Context of Oocyte Donation

Vitrification has become the gold standard for oocyte and embryo cryopreservation. Several commercial kits are available on the market, some are designed for specific developmental stages (e.g. oocytes, zygotes, cleavage-stage embryos or blastocysts) and others are suitable for several stages, therefore termed "universal". Oocytes, cleavage-stage embryos and blastocysts display different levels of resistance to cryopreservation, due to stage-specific properties. While the composition and the exposition protocol of stage specific media are optimized for specific developmental stages, "universal" media display a single composition, therefore exposition protocols should be adapted to each specific developmental stage to ensure optimal survival rates. The main objective of this study is to determine whether the shift from "oocyte specific" vitrification and warming media to "universal" media has an impact oocyte survival, embryological and clinical outcomes.