Effect of storage temperature on sperm cryopreservation

OBJECTIVE: To evaluate the influence of cryopreservation temperature on human sperm motility and morphology. DESIGN: Controlled study, investigator was blinded to the type of cryopreservation. SETTING: University-based andrology laboratory. PATIENT(S): Sixteen semen samples with normal motility and sperm count from men after a fertility work up. INTERVENTION(S): Semen aliquots were either stored in a mechanical freezer at -70 degrees C or in liquid nitrogen at -196 degrees C for 7 days or 3 months. Test yolk buffer was used as a cryoprotectant. With use of a programmable freezing unit, all samples were cooled at a controlled rate. MAIN OUTCOME MEASURE(S): Sperm motility and morphology. RESULT(S): After 7 days of cryopreservation, there was a greater decrease in sperm motility among specimens maintained at -70 degrees C than among those maintained at -196 degrees C (47% versus 39% decrease). The difference in sperm motility was even greater after 3 months of cryopreservation (72% versus 39% decrease). No difference in postthaw sperm morphology was detected among sperm preserved at -70 degrees C versus -196 degrees C. CONCLUSION(S): Sperm cryopreservation at -196 degrees C is superior to cryopreservation at -70 degrees C. Sperm can be stored at -70 degrees C for a short period of time with a relatively modest loss of motility.