Problems with cervical mucus

[Vania]

If cervical mucus is abnormal, it may prevent sperm from entering the uterus or may promote the destruction of sperm.
(See also Overview of Infertility.)
Cervical mucus is secreted by glands in the cervix (the lower part of the uterus that opens into the vagina). Normally, this mucus is thick and impenetrable to sperm until just before release of an egg (ovulation). Then, just before ovulation, the mucus becomes clear and elastic (because the level of the hormone estrogen increases). As a result, sperm can move through the mucus into the uterus to the fallopian tubes, where fertilization can take place.
Abnormal mucus may do the following:

Not change at ovulation (usually because of an infection), making pregnancy unlikely
Allow bacteria in the vagina, usually those that cause infection in the cervix (cervicitis), to enter the uterus, sometimes resulting in the destruction of sperm
Contain antibodies to sperm, which kill sperm before they can reach the egg (a rare problem)

However, problems with cervical mucus rarely impair fertility significantly, except in women who have chronic cervicitis or a cervix that has been narrowed (called cervical stenosis) by treatment for a precancerous abnormality of the cervix (cervical dysplasia).