Fertilization and development of the human oocyte following exposure to cryoprotectants, low temperatures and cryopreservation: a comparison of two techniques

Both glycerol and dimethyl sulphoxide (DMSO) equilibration prior to cryopreservation produced adequate rates of survival and development to the hatching blastocyst stage for mouse oocytes using the two chosen cooling and warming regimes. Successful fertilization of human oocytes and further development of the embryos produced, was achieved following equilibration with DMSO at 0 degrees C. Although fertilization of fresh human ova previously exposed to glycerol was recorded, all oocytes with two pronuclei failed to continue to undergo cell division by 48 h in culture. Following cryopreservation, human oocytes were successfully inseminated after equilibration with both glycerol and DMSO. However, cell division to the 2-cell stage was recorded in only one oocyte which had undergone exposure to DMSO, freezing and thawing. No cell divisions were recorded after glycerol cryopreservation, or even after simple exposure to glycerol. Therefore it appears that DMSO and slow cooling may be the best protocol, although further evaluation will be necessary.