The survival of mouse oocytes shows little or no correlation with the vitrification or freezing of the external medium, but the ability of the medium to vitrify is affected by its solute concentration and by the cooling rate.

As survival of mouse oocytes subjected to vitrification depends far more on the warming rate than on the cooling rate, we wished to determine whether the lack of correlation between survival and cooling rate was mirrored by a lack of correlation between cooling rate and vitrification of the medium (EAFS), and between survival and the vitrification of the medium. The morphological and functional survival of the oocytes showed little or no relation to whether or not the EAFS medium vitrified or froze. We studied if the droplet size and the elapsed time (between placing the droplet on the Cryotop and the start of cooling) affects the result through modification of the cooling rate and solute concentration. Dehydration was rapid; consequently, the time between the placing the droplets into a Cryotop and cooling must be held to a minimum. The size of the EAFS droplet that is being cooled does not seem to affect vitrification. Finally, the degree to which samples of EAFS vitrify is firmly dependent on both its solute concentration and the cooling rate.