Objective: To study the effect of a new human sperm freezing method on the sperm recovery rate and search for an optimal method for cryopreservation of human epididymal sperm.
Methods: We collected semen samples from 76 men with obstructive azoospermia by percutaneous epididymal sperm aspiration and divided each sample into two parts to be cryopreserved with a self-made metal freezing plate (the experimental group) or by slow freezing (the control group), respectively. We measured the percentage of progressively motile sperm (PMS) with the computer-assisted semen analysis system and compared the membrane function, DNA fragmentation index (DFI), acrosin activity and morphological abnormality of the sperm between the two groups before and after cryopreservation.
Results: After thawing, both the percentages of PMS and hypotonically swollen sperm were significantly higher in the experimental than in the control group (［12.0 ± 7.5］% vs ［8.0 ± 5.1］%, P < 0.05; ［22.0 ± 17.5］% vs ［18.0 ± 20.5］%, P < 0.05), though both decreased in comparison with the pre-freezing parameters (［20.7 ± 8.8］% and ［30.0 ± 13.5］%) (P < 0.05). The sperm acrosin activity was remarkably higher in the experimental than in the control group after thawing (［75.2 ± 9.5］ vs ［55.7 ± 8.3］ μIU/106sperm, P < 0.05), though decreased as compared with the baseline (［120.0 ± 10.5］ μIU/106 sperm, P < 0.05). No statistically significant differences were observed between the experimental and the control groups after thawing in the percentage of morphologically abnormal sperm (［98.7 ± 8.8］% vs ［98.5±9.2］%, P > 0.05) or sperm DFI ［38.2 ± 8.5］% vs ［39.5 ± 10.2］%, P > 0.05), though both markedly elevated in comparison with the pre-freezing parameters (［97.2 ± 9.5］% and ［30.8 ± 9.7］%) (P < 0.05). The post-thaw recovery rate of sperm was significantly higher in the experimental than in the control group (［65.2 ± 12.0］% vs ［52.3 ± 18.0］%, P < 0.05).
Conclusions: The self-made metal freezing plate, with its advantages of low cost, high efficiency, and easy operation, can be used as an effective method for cryopreservation of human sperm to achieve a high post-thaw sperm recovery rate, progressive sperm motility, and sperm acrosin activity.
Keywords: assisted reproductive technology; epididymal sperm; recovery rate; semen cryopreservation; metal freezing plate.