Human sperm are subject to natural selection by a number of processes, including chemotaxis and the challenge of the long distance swim from the vagina to the fallopian ampulla in the human female reproductive system. Sperm chemotaxis is the term given to the movement of sperm in the direction of a factor (peptide or chemical) gradient [11]. It is well known that only capacitated sperm are chemotactically responsive [12, 13]. Therefore, sperm selected by chemotaxis are capacitated and may be of better quality. Progesterone secreted from human cumulus cells is a chemoattractant [14] and mediates human sperm chemotaxis [15].
Although sperm selection methods based on chemotaxis [16] and progesterone [17] have recently emerged, devices used in the various studies are very different. The essential distance from the vagina to the fallopian tube where sperm motility is selected is usually disused during the natural selection process during fertilization. The purpose of sperm selection is to obtain better sperm quality, including sperm with normal morphology, and without DNA fragmentation and apoptosis, as these factors influence the outcomes of IVF and ICSI treatments in clinical practice. Sperm with a lower percentage of normal morphological forms is significantly related to a lower probability of ongoing pregnancies after IVF [18].
The relationship between DNA fragmentation in sperm and ART outcomes has been widely investigated, together with fertilization, embryo development, implantation, birth defects in the offspring, and early pregnancy loss [19, 20]. Furthermore, apoptotic sperm percentage has been linked with pregnancy and ART success rates [21, 22].
