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Vitrification is now a widely applied and highly successful approach for cryopreservation in reproductive biology. Rapidly increasing data prove that it is also a highly efficient technique for low-temperature storage of human oocytes. The latest approaches with appropriately selected cryoprotectants, tools and techniques, and properly adjusted parameters allow close to 100% morphological survival rates, and in vitro embryo development, as well pregnancy and implantation rates, comparable with those achieved with fresh oocytes. With standardization of the technique and elimination of biosafety problems by preserving all the positive features, vitrification may become a common part of the everyday routine in a human embryo laboratory, and it may offer a solution for various medical and social situations as well as for simple logistic problems commonly occurring in assisted reproduction.

Recent clinical reports not only show that cryopreserved embryos can be successfully used for human fertility treatment, but also that cryopreserved oocytes may be used successfully as an adjunct to human assisted reproductive technologies. Vitrification is known to establish a glass-like solid state during the cooling process. The high concentration of cryoprotectants and an extremely rapid rate of cooling are responsible for the formation of the solid state, and also prevent formation of intracellular ice crystals. Hence, in theory, vitrification should minimize cryo-injuries, and therefore has great promise for oocyte and embryo cryopreservation. This article describes two pregnancies from vitrified-warmed blastocysts obtained after intracytoplasmic sperm injection fertilization of vitrified-warmed oocytes. Vitrification was employed to cryopreserve the oocytes and the subsequent blastocysts. The results present the intriguing implication that vitrification may serve as an efficient method for clinical oocyte cryopreservation and embryo re-cryopreservation.

This study aimed to evaluate oocyte vitrification efficiency using in-vivo matured (IVO) versus rescued in-vitro matured (IVM) oocytes. The results show that oocyte survival (85% versus 81%), fertilization (86% versus 76%) and cleavage rate (98% versus 89%) was not significantly different in IVO oocytes compared with rescued IVM sibling oocytes. The fertilized oocytes from IVO and IVM groups were cultured to blastocyst stage; however, embryo development was significantly reduced in the rescued IVM group (72% versus 15%). Embryo transfer was only performed with the embryos derived from IVO oocytes on day 5; 42 blastocysts were transferred to 18 recipients; 16 of 18 recipients had positive beta-human chorionic gonadotrophin and a total of 26 fetal cardiac activities were detected in 15 recipients (implantation: 26/42, 61.9%). Ten of the 15 recipients have delivered 19 healthy babies, and the other five pregnancies are still ongoing. These data indicate that the combination of oocyte vitrification and rescued IVM not only yield a new strategy to extend the pool of total fertilizable oocytes, but also demonstrate that the efficiency of vitrified/warmed oocytes can be comparable to fresh oocytes with regard to clinical outcomes.

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