Vitrification of mouse oocytes: Improved rates of survival, fertilization, and development to blastocysts

Abstract
Rall and Fahy's (1985) vitrification procedure for the cryopreservation of 8‐cell embryos was applied to unfertilized mouse oocytes. Unchanged, this method resulted in a mean of 24.1% of vitrified oocytes fertilizing and developing to blastocysts in vitro. Exposure of oocytes to the cryoprotectant media, but without the vitrification, resulted in 30.8% developing to blastocysts. Modifications to the durations of and media used in the dilution and equilibration steps of the procedure produced a final protocol giving a mean of 55.4% of vitrified oocytes and 72.4% of nonvitrified VS1‐exposed oocytes developing to blastocysts; 85.7% of control oocytes develop to blastocysts. Osmotically induced damage was found to be the most important cause of loss of viability in these methods. Cooling of oocytes to 5–8°C during the procedure had no significant effect on their viability. No parthenogenetic activation of oocytes occurred as a result of exposure to the procedure.