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°C or in liquid nitrogen at −196°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°C than among those maintained at −196°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°C versus −196°C.

Conclusion(s): Sperm cryopreservation at −196°C is superior to cryopreservation at −70°C. Sperm can be stored at −70°C for a short period of time with a relatively modest loss of motility.