Dynamic assessment of human sperm DNA damage II: the effect of sperm concentration adjustment during processing.

PURPOSE: To evaluate the effect of sperm concentration adjustment in human ejaculates on the sperm DNA quality and longevity.

METHODS: Semen samples were obtained from 30 donors with a normal spermiogram. Following centrifugation, the sperm pellet was resuspended in PBS, and the sperm concentration adjusted to 200, 100, 50, 25, 12, and 6 × 106 /mL. Each set of samples was incubated at 37 °C for 24 h, and the sperm DNA damage was assessed using the chromatin-dispersion test following 0 h, 2 h, 6 h, and 24 h of incubation.

RESULTS: Sperm DNA fragmentation (SDF) did not differ between the selected experimental conditions at T0; however, Kaplan-Meier estimates for survival showed significant differences with respect to the dilution and time (all P values were smaller than .001). DNA fragmentation in semen samples adjusted to 200 × 106 /mL was approximately 3.3 times higher when compared to samples containing 25 × 106 /mL and 3.9 higher in comparison with samples adjusted to 12 × 106 /mL following 2 h of in vitro incubation. Although there was evidence of individual variation in SDF during the incubation period, the general finding was that lower sperm concentrations resulted in a slower rate of DNA fragmentation.

CONCLUSIONS: Incubation of spermatozoa for ART purposes should be done following a concentration adjustment below 25 × 106 /mL in order to avoid a higher susceptibility of the sperm DNA molecule towards fragmentation.