Concentration of glycerol required for optimal survival and in vitro fertilizing capacity of frozen sperm is dependent on cryopreservation medium.

Sperm survival and in vitro fertilizing capacity were examined following cryopreservation with three concentrations of glycerol (0, 2, and 7.5%) and four cryopreservation media. Post-thaw motility and motility index increased with increasing concentrations of glycerol. Post-thaw velocity, linearity, percentage of zona-free hamster oocytes penetrated, and penetrations per oocyte were greater following freezing with 2 or 7.5% glycerol than with 0% glycerol. A significant interaction between media and glycerol was observed for motility, velocity, linearity, motility index, and percentage of oocytes penetrated. These results suggest that the concentration of glycerol required for optimal survival and in vitro fertilizing capacity of human sperm following cryopreservation is dependent on the type of medium used for freezing.