Inter-center variation in the efficiency of sperm DNA damage reduction following density gradient centrifugation

This was a prospective multicenter study aiming at comparing the efficiency of sperm selection by density gradient centrifugation (DGC) in reducing sperm DNA fragmentation (SDF) in different ART centers. The study was designed using 290 semen samples collected from 10 different ART centers performing artificial insemination, in vitro fertilization and blind assessment of SDF at the University facilities. The results showed that while there was a significant reduction in the SDF levels in sperm isolated from the gradient centrifuged pellet (DGC) compared to neat semen samples (NSS), there was also significant inter-center variability in the efficiency to reduce SDF values by DGC (78.5% to 29.2%). Surprisingly, for some patients, the level of SDF actually increased following sperm selection. The main conclusions derived from this study were that 1) isolation of sperm from the gradient pellet by DGC must be performed using validated, optimized protocols; 2) routine comparison of SDF values in NSS semen and in processed sperm after DGC or swim-up must be recommended as part of the internal quality control (QC) of ART laboratories to test the efficacy of sperm processing; and 3) SDF values in processed spermatozoa should be obtained to compare with the pregnancy rate when insemination or fertilization is about to be performed, otherwise, attempts to predict pregnancy outcome from SDF could be biased or are essentially meaningless.