O-12: Evaluation of Human Spermatozoa Resistance to Cryoinjury after Repeated Cycles of Thaw-Refreezing Using of Cryovial and Straw

Background: Sperm storage via freezing has been useful for men who have difficulty masturbating during assisted reproductive technology (ART) programs and before impotency caused by chemotherapy, vasectomy, and other procedures. Studies were undertaken to evaluate the extent of cryoinjury to both semen and sperm after repeated freezing and thawing in oligozoospermic and normozoospermic samples using of cryovial and straw. Materials and Methods: Semen specimens were obtained from normal and oligozoospermic individuals who required disposal at the sperm bank. Specimens were thawed and an aliquot was removed for analysis. The remaining specimens were refrozen without removing the cryomedia. Repeated freeze-thaw cycles were performed until no motile sperm were observed. Sperm motility, number of motile spermatozoa and viability were determined after thawing. Resistance to cryoinjury was compared between groups and also after each refreezing cycle within groups. Resistance to cryoinjury also was assayed in each group using of cryovial and straw. Results: The results showed that normozoospermic and oligozoospermic sperm survived after 3 (cryovial) and 4 (straw) repeated freeze-thaw cycles. There were no significant differences in recovery percentages for motile and vital normal sperm in thaws 1 to 3 (cryovial) and 1 to 4 (straw) of normozoospermic and oligozoospermic unwashed (u) and washed (w) samples, but percentage motility and total number of motile spermatozoa were significantly lower in the oligozoospermic one. The percentage of abnormal sperm also reduced after each freezing-thawing. However, there was significant percentage in the recovery of motile and vital sperm between each thaw using both cryovial and straw for u and w samples (p<0.01) during thaws 1 to 4 in the normozoospermic and oligozoospermic groups. Repeated cycles of thaw-refreezing were done until 6 times for normozoospermin and resistance of sperm was more using of straw in comparison to cryovial (p<0.05). Conclusion: Human spermatozoa resist repeated cryopreservation using the liquid nitrogen vapor method. Normozoospermic specimens withstand refreezing for an average two cycles longer than oligozoospermic ones. Resistance to repeated cryoinjury was related to the initial semen quality. Thus, leftover washed sperm in laboratories that perform in vitro fertilization can be frozen, thawed, and refrozen several times without loss of the sperms’ motility and viability. This approach has tremendous benefits for men who have difficulty producing sperm and for those with low and declining sperm counts