Quantitative sperm mucus penetration: modified formulae for calculating penetration efficiency.

In 1980 Katz et al. derived a formula for the percentage of successful collisions (PSC) as a quantitative measure of sperm-cervical mucus penetration efficiency. The use of PSC waned after its validity was questioned by reports of values >100% and the observation that PSC varied with the cross-sectional area of the mucus column. The aim of the present study was to develop a more accurate measure of mucus penetration efficiency by correcting the original formula for the effects of sperm depletion in the semen reservoir. Two formulae were derived using different models for the sperm-mucus interaction: (i) each motile spermatozoon was assumed to have an equal chance of mucus penetration on collision; (ii) a select subpopulation of spermatozoa was assumed to penetrate with 100% efficiency on collision. Both modified formulae gave PSC values higher than the original estimates. Under the experimental conditions employed in this work, where large capillaries were used, the depletion corrections ranged from 4 to 46% (n=8, mean 20%) for model (i) and from 190 to 320% (n=8, mean 250%) for model (ii). The invariance of PSC (ii) results with respect to capillary cross-sectional area (1.52 mm2, 31.1%; 5.4 mm2, 28.2%) suggests that the assumptions of model (ii) provide the more accurate description of the sperm-mucus interaction.