Survival of human sperm following controlled- and noncontrolled-rate cryopreservation

The purpose of this study was to develop a noncontrolled-rate (NCR) method of freezing semen in cryovials which could be used as a backup to controlled-rate (CR) freezing when the CR freezer was being utilized for freezing of human embryos or oocytes. Semen was frozen with three concentrations of glycerol (0%, 3.75%, 7.5%) in cryoprotective media in a CR freezer or using a newly developed NCR method of freezing. Semen was thawed in 40 degrees C water or in air at room temperature (RT). Controlled-rate freezing and 40 degrees C thawing resulted in significantly greater postthaw sperm motility and motility index compared with NCR freezing and RT thawing. Sperm velocity and linearity were not significantly effected by rate of freezing or thawing except when there was no glycerol present in the cryoprotective media. Postthaw motilities following CR-40 degrees C, NCR-40 degrees C, CR-RT and NCR-RT freezing-thawing were 25.6%, 24.8%, 21.6% and 18.3%, respectively. Because NCR freezing resulted in only a 0.8% decline in motility compared with CR freezing when semen was thawed at 40 degrees C it appears that this new NCR method of freezing can be successfully used as a backup to CR freezing when the CR freezer is being used for embryo or oocyte cryopreservation.