Received December 12, 2017
Accepted June 11, 2018

Cryopreservation of human spermatozoa is fundamental in assisted reproductive technology. At present, slow freezing techniques are widely used for sperm cryopreservation. Recently, sperm vitrification has been proposed as an alternative to slow freezing. The aim of this study is to compare the efficiency of slow freezing, after thawing with that of ultra-rapid freezing, and to determine the level of DNA fragmentation in the post-thaw samples, after both cryopreservation techniques are applied to normal human semen samples. Ultra-rapid freezing is a method that only differs from conventional ultra-rapid freezing in the use of sucrose as cryoprotectant. In experiment 1, 24 semen samples were used to compare sperm recovery rates after slow and ultra-rapid sperm freezing. In experiment 2, 18 semen samples were used to compare the post-thaw sperm DNA fragmentation, after both cryopreservation techniques were applied to the same samples. In experiment 1, no significant differences were obtained in sperm concentration recovery rates, although slow freezing showed a lower progressive motility rate than ultra-rapid freezing (16.6 ± 7.4% vs. 34.7 ± 10.2%), and higher non-progressive and immotile sperm counts (9.0 ± 4.0% vs. 7.6 ± 2.8%; and 74.4 ± 10.1% vs. 57.8 ± 10.3%, respectively). In experiment 2, sperm DNA fragmentation after thawing, was significantly higher than post-slow freezing compared to fresh post gradient processing and the post-ultra-rapid freezing samples (47.3 ± 13.4% vs. 9.1 ± 3.7% vs. 14.6 ± 4.6%, respectively). Sperm ultra-rapid freezing may be an alternative to slow freezing with better recovery results and less apparent DNA damage.