Cervical mucus viscoelasticity and sperm velocity are correlated and concentration-dependent in Vitro

Abstract

Background Mucus in the endocervix serves as fertility gatekeeper in the reproductive tract through hormonally regulated changes in biophysical properties. Cervical mucus can thicken to prevent ascension of sperm into the upper reproductive tract or thin to permit fertilization. Current reproductive studies of mucus viscoelastic properties rely on subjective visual appraisal of cervical mucus changes. Our goal was to use particle tracking microrheology (PTMR) to objectively assess cervical mucus viscoelastic properties and associate these measurements with in vitro measures of sperm velocity. Methods Using cervical mucus obtained from rhesus macaques ( Macaca mulatta ) at necropsy, we used to PTMR to measure viscoelasticity (η*) under stepwise, serial dilutions. In parallel we measure sperm velocity using custom sperm tracking and analysis workflows. Results We report that both mucus η* and sperm velocity displayed a concentration-dependent behavior, where η* increased as mucus concentration increased, and sperm velocity correspondingly decreased. Viscoelasticity and sperm velocity were strongly negatively correlated (p < 0.001). Conclusions PTMR and sperm tracking in mucus provide quantitative measure of viscoelastic mucus changes. PTMR is potentially a method for quantitatively assessing fertility potential in the cervix that could be applied to both infertility and contraceptives studies.