Sperm swim-up techniques and DNA fragmentation

BACKGROUND: Swim-up techniques for sperm separation may have detrimental ef fects on sperm DNA. We wished to determine whether the normal swim-up metho d with centrifugation used in our laboratory, which involves a centrifugati on step, was harmful to sperm compared with swim-up without centrifugation. METHODS: Semen samples were obtained from patients undergoing IVF or andro logy assessment. An aliquot was removed for fixation and subsequent DNA fra gmentation determination. The remaining sample was divided into two equal p arts, which were subjected to swim-up either with (normal swim-up) or witho ut (direct-swim-up) centrifugation. Semen analysis was performed both befor e and after swim-up. DNA fragmentation, in spermatozoa previously fixed in 4% paraformaldehyde, was assessed by the terminal transferase-mediated DNA end-labelling procedure (TUNEL). The percentage of spermatozoa with DNA dam age after each swim-up technique was compared with that in the original sem en sample. RESULTS: DNA damage was <5% in most samples. No significant chan ge in DNA fragmentation was observed between the two swim-up procedures, al though the 'normal' swim-up sample had significantly less DNA fragmentation than the pre-swim-up sample. CONCLUSIONS: We conclude that our normal swim -up technique caused no more DNA damage to spermatozoa from normal semen sa mples than a direct swim-up technique that involved no centrifugation step.