Figure 2.Variability of semen analysis results in a fertile sperm donor. C, sperm concentration; V, semen volume; M, total motility; MI, motility index-product of grade and percentage of sperm with progressive motility graded 0 to 3. (Mallidis C et al: Variation of semen quality in normal men. Int J Androl 14:99-107, 1991. Used by permission Blackwell Scientific Publications.)