A new quantitative test for sperm penetration into cervical mucus

A new experimental and theoretical procedure is described for characterizing the penetration of spermatozoa into cervical mucus in vitro. Semen is introduced to a prescribed volume of mucus contained in a flat capillary tube. Use of the tube enables the surface area of semen-mucus contact to be fixed, and provides excellent visualization of sperm movement in the mucus. The time interval of semen-mucus contact is also controlled. The number of motile sperm and their swimming speeds are determined in both the semen and mucus by hemocytometer counts and simple time-exposure photomicrography. The assay provides two new measures of the sperm-mucus interaction. The number of successful sperm entries into the mucus is compared with the number of original collisions between seminal sperm and the semen-mucus interface. The comparison is expressed as a ratio of the numbers of sperm in these two groups, viz., PSC = percentage of successful collisions. The vitality of spermatozoa that do succeed in entering the mucus is assessed by comparing their swimming speeds with those of sperm in the semen. This second comparison is also expressed as a ratio, viz., VR = velocity ratio = mean swimming speed in mucus/mean swimming speed in semen. The clinical application of the method to human semen and cervical mucus is described, and sample results are presented.