Cryogenic preservation of low-quality human semen

The article describes the technical strategies for clinical cryogenic preservation of low-quality human semen. To compensate for sperm dilution resulting from the use of a cryogenic medium, ejaculated semen was concentrated before freezing by means of continuous-step density gradient centrifugation. Freezing was simplified by employing the carbon dioxide pellet method with KS-II cryogenic medium, which contains Pluronic F-68, a nonionic detergent, to solubilize egg yolk (a major cryogenic protectant). Semen of less than 50% motility (n = 23) was processed and then cryogenically preserved. Sperm concentration was increased by a factor of 1.8 +/- 0.96 (n = 23). Sperm motility was improved from 35.9% +/- 13.9% to 69.4% +/- 10.8%. Even after thawing 59.4% +/- 17.5% motility remained, with a mean survival rate of 85% +/- 14%. The concentration of sperm and improved sperm motility by the use of the continuous-step density gradient and the high survival rate ensured by the carbon dioxide pellet method with KS-II cryogenic medium compensated for the lowering of sperm quality during cryogenic preservation.