The purpose of our research was to determine how two cryopreservation protocols affect viability and DNA fragmentation in human sperm. The research included 69 volunteers with minimum 15*106 sperm cells per millilitre and 40 % motility. Each human semen sample was divided into three aliquots. One aliquot was evaluated as native sperm sample, one was slow freezed and one was vitrified. Slow freezing was performed by the procedure currently used in Division of Obstetrics and Gynaecology, University Medical Centre Ljubljana. Native sperm samples and samples after cryopreservation were evaluated for sperm motility, viability, maturity and DNA fragmentation. Sperm maturity was evaluated by protamine aniline blue staining and by hyaluron binding assay. DNA fragmentation was evaluated using flow cytometry. Our results demonstrate that cryopreservation decreases sperm viability and motility, while it increases DNA fragmentation in human sperm. No significant difference in sperm maturity was found. Vitrification did not enable better viability, motility or DNA preservation than slow freezing. We correctly expected decreased viability, motility and increased DNA fragmentation in human sperm samples following cryopreservation compared to native human semen, but we incorrectly expected greater differences between sperm samples after slow freezing and after vitrification. Nonetheless, some other research and the fact that vitrification is routinely used for oocyte and embryo cryopreservation suggest vitrification could become the method of choice for human semen cryopreservation as well.
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