Poor hypo-osmotic swelling test results from cryopreserved sperm despite preservation of sperm motility.

Cryopreservation thawing of sperm leads to decreased motile density. Most donor programs select for cryopreservation a male with a high initial motile density and if the post-thaw semen has a motile density over 10 x 10(6)/ml, the specimen is thought to represent a fertile specimen. Some recent data suggest that males with normal motile densities but subnormal hypo-osmotic swelling (HOS) tests may be infertile. A study was thus performed to see if males with an adequate motile density after cryopreservation may still demonstrate membrane damage as evidenced by decreased viability and a poor HOS test. The semen species from seven men with motile densities greater than or equal to 10 x 10(6)/ml after freeze-thawing were evaluated for HOS changes and viability. Despite preservation of normal motile density, all 7 men had HOS scores below 50% following cryopreservation (though all were significantly above this level pre-freeze). The mean viability and HOS scores prefreezing were 70 +/- 9.7 and 68.5 +/- 9.5, and post thaw they dropped to 33.7 +/- 6.9 and 32.8 +/- 6.2. These data suggest a mechanism for impaired fertility even with adequate motile density of a thawed specimen that had been cryopreserved.