A review of cervical mucus and sperm interactions in humans

Cervical mucus is an aqueous or gel mixture of fluids, ions and compounds, and cells, primarily produced by the endocervical epithelium. The amount secreted varies with menstrual phase and compositions changes under hormonal influence. Sodium shows the greatest concentration change at ovulation but does not change early enough to be of value in natural family planning practice. Dried mucus has a fern appearance due to NaCl crystals at ovulation. Other substances, less clearly related, are too difficult to analyze or in too low concentration. Soluble proteins, amino acids, and simple sugars show wide fluctuation and probably influence sperm penetration and nutrition. One function of mucus is antimicrobial activity of leukocytes, which decreases at midcycle. Another, sperm transport, is a function of estrogen's effect on mucus rather than ovulation. Sperm concentration in the mucus column is maximal from 15 minutes to 2 hours after vaginal deposition. Rapid penetration into cervical mucus favors sperm survival because of its optimal pH. Infertility may be caused by immunoglobulins or spermagglutinins in cervical mucus. To date, no constituent of cervical mucus has been identified which undergoes an easily detectable change 4 days before ovulation. Several potential methods for use in natural family planning are suggested.