EFFECT OF AN INTERMEDIATE HOLD WITH VAPOR FREEZING ON SUBSEQUENT HYPOOSMOTIC SWELLING IN THAWED SPERM

Cryopreservation and thawing of sperm exerts an adverse effect on func tional integrity of the sperm membrane as measured by the hypoosmotic swelling (HOS) test. Supercooling using the liquid nitrogen (LN(2)) va por technique may damage membranes by favoring ice crystal formation. Slight slowing of the cooling process may allow escape of intracellula r fluid. This study was conducted to evaluate modification of the LN(2 ) vapor technique by employing an intermediate hold in a freezer (to s low down the rate of cooling) on HOS scores on specimens thawed 1 mont h after freezing. Semen samples were obtained from male partners of in fertile couples with a requirement of a baseline HOS score <70% but gr eater than or equal to 60%. The HOS test was performed on the unprepar ed semen sample prior to freezing and immediately post-thaw 1 month la ter on the aliquot frozen with LN(2) vapors only vs. the equal fractio n subjected to an intermediate hold. The mean initial HOS score was 68 .5% and was 47% in thawed specimens that had been cryopreserved with a nd without an intermediate hold. There were no differences in the perc entage of specimens exhibiting a >50% HOS score following vapor freeze (70%) or vapor freeze with a hold (74%). Thus, these data do not demo nstrate any advantage of slowing the vapor freezing process by utilizi ng an intermediate hold.