Variation in mean human sperm length is linked with semen characteristics

Abstract

Are there any links between the length measurements of sperm components (head, midpiece, flagellum, total sperm length and the flagellum:head ratio) and data obtained during semen analysis? Both the mean measurement and the variation in the lengths of sperm components are related to characteristics of semen. Studies in non-human species have shown that sperm morphology (size and shape) is associated with testes productivity and the consistency of sperm manufacture. However, no study to date has investigated whether there are relationships between the size and consistency of human sperm components, and measures of semen characteristics, including sperm numbers and how well they swim. A retrospective laboratory study of the semen provided by 103 randomly selected men from a 500-man cohort who enrolled into the study between April and December 2006. Men attending Sheffield Teaching Hospital NHS Foundation Trust for semen analysis as part of investigations for infertility and whose ejaculates were found to contain sperm. The mean flagellum length and the mean total sperm length were positively associated with semen characteristics measured manually, but were not associated with the sperm swimming speed measured by computer-aided sperm analysis. Ejaculates with a lower variation in the length of sperm components contained sperm that were more likely to be motile. The mean sperm length components accounted for up to 9% of the variance in semen characteristics, while the coefficient of variation accounted for up to 21%. The sperm examined were obtained from men undergoing fertility investigations and so these results may not reflect men in the general population. Sperm length measurements may provide a useful insight into testis function and the efficiency of spermatogenesis. This study was supported by funding from the University of Sheffield. The authors declare no conflicts of interest.