Long-term cryostorage of sperm in a human sperm bank does not damage progressive motility concentration.

BACKGROUND The use of quarantined cryopreserved semen is mandatory in donor insemination programs. Whether sperm cells can survive and retain their ability to fertilize after long-term storage remains a controversial issue. The objective of this study was to determine the effect of the duration of cryostorage in liquid nitrogen on the sperm cells' progressive motility concentration (PMC) in a large study group. METHODS A total of 2525 thawed sperm specimens, packed in straws and donated by 72 sperm bank donors for intrauterine insemination (IUI), were evaluated in an assisted reproduction institute. PMC was recorded after 0.5-14.4 years of cryostorage. RESULTS The mean (+/-SD) value of PMC of all study samples was 10.8 +/- 3.3 x 10(6)/ml after freezing/thawing and before cryostorage (T0), and 12.3 +/- 2.9 x 10(6)/ml after storage and before using the specimen for IUI (T1, P < 0.0001). Specimen storage for different lengths of time revealed that storage duration had no significant influence on the PMC of the specimens (r = -0.03, P = 0.08). The PMC of partially filled straws was lower than in full straws. Cryostorage duration made no difference in the PMC of raw and washed sperm specimens. CONCLUSION Prolonged storage of donated sperm in liquid nitrogen had no influence on the PMC of the specimens and therefore should not alter the fertilization potency of donated sperm. The high post-storage values of the PMC compared with the pre-storage PMC values was probably an artifact of the small volume of the pre-storage sample.