Prolonged semen incubation alters the biological characteristics of human spermatozoa.

Objective: The present study assessed the biological characteristics of human spermatozoa at different time intervals (0, 1, 1.5, and 2 hours) after incubation at 37°C.

Methods: Twenty-five normozoospermic semen samples were incubated at 37°C. Incubation was performed at four time intervals of 0 (after liquefaction), 1, 1.5, and 2 hours. The samples were evaluated for sperm parameters at each time interval.

Results: The rate of sperm progressive motility decreased at 1.5 hours compared to 0 hours as well as 2 hours compared to 1 hour and 0 hours. The rate of non-motile spermatozoa also decreased after 2 hours compared to after 0 hours. No significant changes were observed in sperm viability (p=0.98) and non- progressive motility (p=0.48) at any time intervals. Abnormal sperm morphology increased at 1.5 hours of incubation time (p<0.001). No significant changes were observed in DNA fragmentation at 1 hour compared to 0 hours (median [interquartile range]: 19.5 [4] vs. 19 [4]), as well as at 1.5 hours compared to 1 hour (20 [5]). However, a significant increase in DNA fragmentation was observed at 1.5 hours compared to 0 hours. The mitochondrial membrane potential decreased remarkably after 1 hour of incubation time. No significant differences were observed in the acrosome reaction or malonaldehyde levels at any time point (p=0.34 and p=0.98, respectively).

Conclusion: The incubation of normozoospermic samples before use in assisted reproductive technology should be less than 1.5 hours to minimize the destructive effects of prolonged incubation time on general and specific sperm parameters.