DNA fragmentation in morphologically normal spermatozoa: how much should we be concerned in the ICSI era?

Intracytoplasmic sperm injection (ICSI) has revolutionized the treatment of male infertility. However, there are still unanswered questions about the safety of this technique. During ICSI, only morphologically normal and motile spermatozoa are typically used to fertilize an oocyte. We recently reported that in infertile men, spermatozoa with apparently normal morphology may have DNA fragmentation. This finding consequently raised the possibility that spermatozoa with normal-shaped appearance but with DNA fragmentation could be mistakenly selected to fertilize oocytes during ICSI. This concern became more clinically significant following the subsequent finding that the presence of an increased proportion of normal spermatozoa with damaged DNA was negatively associated with embryo quality and pregnancy outcome after ICSI. Herein, we propose and discuss the hypothesis that the examination of DNA integrity in the subpopulation of highly motile (hence viable) and morphologically normal cells (and not in the total sperm population) may provide optimized information in prediction of ICSI success. More importantly, this new way of evaluation may provide reassurance about genomic normalcy and minimal risk of transmission of genetic disease and guide the development of improved methods of selection of spermatozoa with intact DNA to be used in assisted reproduction.