Factors affecting sperm motility. II. Human sperm velocity and percentage of motility as influenced by semen dilution.

Spermatozoal velocity and percentage of motility were analyzed objectively with the multiple exposure photography method before and after specimens from fertile and infertile men were diluted in their own seminal plasma or normal saline. No significant change in percentage of motility was found in samples diluted up to 1:6 in both kinds of diluents. However, a significant relative increase (up to 25% of the original velocity) was found when a specimen was diluted with its own seminal plasma, and an even greater increase (up to 37% of the original velocity) was found when it was diluted with saline. Compared with undiluted specimens, there was no delayed effect on spermatozoal motility when semen was diluted with saline after up to 4 hours' incubation time. Contrary to the findings in animal and human semen described by others, there was no deleterious effect on sperm motility with this kind and rate of dilution and duration of time. The assumption that the increase in sperm velocity caused by dilution is not excitatory but is due only to a decrease of seminal fluid viscosity and a reduced number of spermatozoa which interfere with sperm free movement is discussed. We recommend evaluation of spermatozoal motility in diluted specimens in addition to evaluation of the original specimen in any routine semen analysis in order to determine true spermatozoal motility potential under optimal conditions.