Cervical Mucus and Contraception

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The cervical mucus is a viable site for contraceptive action. Hormonal contraceptive methods alter cervical mucus and other potential contraceptives also could act specifically on cervical mucus. Local hormones or chemicals which could be placed in the vagina or cervix might alter mucus without systemic effects. Thus far even those hormones placed cervically or vaginally probably affect cervical mucus by systemic absorption. Cervical mucus is a gel. It is composed of an insoluble glycoprotein matrix and an aqueous phase that contains soluble small molecules such as sodium chloride. The solid phase is a 3-dimensional network made of a glycoprotein. Although some investigators disagree normally it appears that mucus is produced and secreted by the endocervical cells at a fairly constant rate throughout the cycle. Under the influence of estrogen unopposed by progesterone vascular permeability of water and solutes increases causing an increased amount of cervical secretion to be present. This is the receptive late follicular phase mucus. When the water and solute content is low either when estrogen is low or progesterone elevated the glycoprotein filaments become brittle and lose their parallel alignment with the axis of the cervical canal. Scanning electronmicrographs of the cervical mucus throughout the cycle demonstrate these changes in alignment of the filaments. The water content of the mucus increases under the influence of high mid-cycle estrogen levels. Almost immediately after ovulation as serum progesterone increases to a level of 1-2 ng/ml cervical mucus becomes thick viscous and gelatinous. The combination pill and the progestogen-only pill (POP) show the same effect as noted during the luteal phase. Even with the low dose of progestin in the POP cervical mucus is altered. The pregnancy rate for the POP is higher than for the combination pill. Since the POP does not always suppress ovulation the contraceptive action is assumed to be related to changes in cervical mucus penetrability and effects on the endometrium. Intracervical devices releasing a progestogen have been developed in an attempt to maximize local hormonal effects and minimize systemic effects. Despite ovulation patients have shown contraceptive effectiveness which is most likely due to changes in mucus and endometrium. The continuation rate for the intracervical device has been similar to that of the IUD with a lower expulsion rate. Yet contraceptive effectiveness most likely will not be adequate without a higher release rate of levonorgesterel. Lipid-soluble drugs can be excreted directly into cervical mucus. An oral medication could have potential spermicidal cervical action. Modern natural family planning depends on changes in cervical mucus to help identify the safe period. Cervical mucus is useful if the daily changes during the cycle can be appreciated by the patient.