Full-complement lytic activity was measured in human midcycle cervical mucus, using a sensitive 51Cr release hemolytic assay. The level measured was 11.5% of the activity of complement in an equal volume of undiluted human serum. The relevance of this level of complement to complement-dependent sperm-immobilizing antibody activity was studied. After 1 hour's incubation with mucus levels of complement, immobilization of about 50% of spermatozoa occurred and after 3 hours' incubation, immobilization of about 70% of spermatozoa occurred.
Price, R. J., & Boettcher, B. (1979). The presence of complement in human cervical mucus and its possible relevance to infertility in women with complement-dependent sperm-immobilizing antibodies. Fertility and Sterility, 32(1), 61–66. https://doi.org/10.1016/S0015-0282(16)44117-8