Feasibility of refreezing human spermatozoa through the technique of liquid nitrogen vapor

To assess the feasibility of refreezing human semen using the technique of liquid nitrogen vapor with static phases.

Twenty samples from 16 subjects who required disposal of their cryopreserved semen were thawed, corresponding to 6 cancer patients and 10 participants in the assisted reproduction (AR) program. Samples were refrozen using the technique of liquid nitrogen vapor with static phases, identical to the one used for the initial freezing, and thawed again after 72 hours. We assessed the concentration of motile spermatozoa, total and progressive percent motility and spermatic vitality, according to criteria of the World Health Organization (WHO), as well as spermatic morphology according to the strict Kruger criterion, after the first and after the second thawing.

We observed a significant decrease in all the parameters evaluated between the first and the second thawing. Median values for the concentration of motile spermatozoa decreased from 2.0x10(6)/mL to 0.1x10(6)/mL (p < 0.01); total percent motility from 42% to 22.5% (p < 0.01); progressive percent motility from 34% to 9.5% (p < 0.01); vitality from 45% to 20% (p < 0.01); and morphology from 5% to 5% (p = 0.03). There was no significant difference in the spermatic parameters between the cancer and assisted reproduction groups, both after the first and after the second thawing. We observed that in 100% of cases there was retrieval of motile spermatozoa after the second thawing.

Refreezing of human semen by the technique of liquid nitrogen vapor allows the retrieval of viable spermatozoa after thawing.