ABSTRACT
Cryopreservation of mammalian and human oocytes has been significantly improved by the refined slow-freezing methods and new vitrification techniques.1-12 The slow-freezing method using a programmed cryo-machine is traditionally employed for the cryopreservation of oocytes.13 This procedure usually take several hours. Vitrification is an important alternative method. With high concentrations of cryoprotectants and a fast cooling rate, it transforms cells into an amorphous glassy state, instead of ice crystal formation.14,15
Vitrification is time-saving and does not require special equipment. The vitrification methods may replace the slow-freezing method for cryopreservation of oocytes.16-19
The recent improvements of vitrification include the concepts of reduction of concentration of cryoprotectants, increase of cooling and warming rates, recovery of meiotic spindle, and timely fertilization.
