Evaluation of Serial Thawing-Refreezing on Human Spermatozoa Resistance Using Cryovials and Straws

BACKGROUND We designed this study to detect the cryoinjury rate on human sperm after serial freezing and thawing, taking into consideration the effects of using cryovials and straws. MATERIALS AND METHODS In this experimental study, semen specimens obtained from 15 subjects were divided into normozoospermic and oligozoospermic groups. Each of the normozoospermic and oligozoo spermic semen specimens were additionally divided into two groups: i. washed and ii. unwashed. Specimens were repeatedly freeze-thawed by using cryovials and straws with the fast liquid nitrogen vapor method, until no motile sperm remained. Sperm motility, recovery, and morphology rate were then determined after thawing, and compared between the groups while taking into consideration the effects of using cryovials and straws. RESULTS Motile spermatozoa were observed in all normozoospermic samples up to thaw 6 with both cryovials and straws while in oligozoospermic specimens up to thaw 4 (straw) and thaw 3 (cryovial) in the freeze-thawing cycle. Normozoospermic sample analysis showed no significant difference in morphology rate. There was a significant increase in motility and recovery percentages for washed samples, which was observed with straws in compared to the unwashed groups. Oligozoospermic sample analysis indicated a significant increase in motility, recovery (p<0.01), and morphology (p<0.001) rates in washed specimens compared to unwashed specimens using straws. The importance of washing sperm was obvious for oligozoospermic specimens. CONCLUSION Normozoospermic sperm resisted freezing longer than oligozoospermic sperm. Use of straws and cryovials made significant differences in motility, recovery, and morphology of sperm in each thaw. This difference was slightly higher for oligozoospermic specimens. Results indicated that the percentage of motility was higher for washed normozoospermic specimens in each thaw when straws were used, whereas the percentage of motility, recovery, and morphology were promoted after frozen oligozoospermic specimens were washed using straws.