Vitrification of mouse oocytes using a nylon loop

Cryopreservation of mouse oocytes was improved by the use of ultra-rapid vi trification using a nylon loop of 0.5 mm diameter. Oocytes that were vitrif ied using the loop survived at high rates and were fertilized following a s mall hole being made in the zona pellucida (69.8%) and developed to the bla stocyst stage in culture (67.4%) at similar rates to that of oocytes that w ere not cryopreserved. Blastocysts resulting from oocytes vitrified using t he nylon loop had similar development of the inner cell mass and trophectod erm as blastocysts from non-cryopreserved oocytes. In contrast, oocytes tha t were cryopreserved using a slow-freezing protocol where most of the Naf i s replaced with choline had lower rates of fertilization (39.5%), reduced d evelopment to the blastocyst stage (25.7%), and blastocysts had reduced dev elopment of the inner cell mass. Blastocysts derived from oocytes that were vitrified with the nylon loop were able to implant (88.0%) and develop int o fetuses (56.5%) at significantly higher rates compared to blastocysts der ived from oocytes that were slow-frozen (52.4 and 26.2%, respectively). Vit rification of mouse oocytes using the nylon loop results in the retention o f viability of the oocytes and subsequent embryos. (C) 2001 Wiley-Liss, Inc .