Introduction: Cryopreservation of human sperm is considered a routine practice in assisted reproduction laboratories. Semen samples are mainly cryopreserved as a back-up for procedures, donor sperm, and validation of samples from human immunodeficiency virus-positive patients. Human immunodeficiency virus semen samples generally result in a low yield of purified spermatozoa after decontamination. These samples need to be cryopreserved for later use. Unlike conventional cryopreservation, vitrification does not use harmful cryoprotectants, thereby potentially reducing sperm damage. Vitrification is not yet common practice for sperm cryopreservation in assisted reproduction. The aim of this study was to establish the feasibility of utilising vitrification as an alternative to current conventional cryopreservation of spermatozoa.
Methods: Semen samples were collected from human immunodeficiency virus-negative patients seeking diagnostic assistance from the unit. All samples were processed according to the unit’s standard protocol. For Study 1A (n=10) washed samples were divided and cryopreserved using three different cryopreservation media, and two different freezing protocols. In Study 1B (n=15), washed samples were divided and preserved using cryoprotectant-free vitrification in 100 μl, 300 μl and 500 μl volumes. For Study 2 (n=35) washed samples were split and cryopreserved using cryoprotectant-free vitrification (utilizing the volume that resulted in the highest quality spermatozoa in Study 1B) and conventional slow freezing (using the medium and protocol that resulted in superior quality spermatozoa in Study 1A). Post thawing, motility and kinetic parameters (Studies 1 and 2), viability (Study 1), mitochondrial membrane potential (Study 2), and DNA fragmentation (Study 2) of the two groups were compared.
Results: Study 1A indicated that cryopreserving spermatozoa using Freezing Medium resulted in the highest quality spermatozoa with regards to motility and viability (p<0.05). Comparing the two preservation protocols, no conclusion could be reached on which protocol yielded superior results (p>0.05). The RBL freezing method is shorter, simpler and requires less equipment, and was therefore deemed the preferred method. Study 1B showed that the larger vitrification volumes (300 μl and 500 μl) yielded better spermatozoa in terms of motility and viability (p<0.05). No significant difference was observed with respect to the 300 μl and 500 μl vitrification volume groups. For practical reasons, 300 μl volumes will provide sufficient sperm for any procedure and, the intermediate volume ensures that more than one straw can be preserved. Study 2 found that cryoprotectant-free vitrification resulted in spermatozoa with significantly higher mitochondrial membrane potential and significantly lower apoptosis post thawing (p<0.05).
Discussion: Conventional cryopreservation methods may compromise various sperm parameters and final yield. In this study, cryopreservation and cryoprotectant-free vitrification had equivalent outcomes with respect to sperm motility. However, the latter method yielded superior results in terms of ΔΨ and DNA sperm fragmentation. In conclusion, vitrification is an easy, rapid and more affordable technique that requires no special equipment. Using vitrification for purified sperm samples of patients could potentially result in a better post thaw quality for ART procedures.