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Problems With Mucus in the Cervix

by Robert W. Rebar, MD

If mucus in the cervix is abnormal, it may prevent sperm from entering the uterus or may promote the destruction of sperm.

Normally, mucus in the cervix (the lower part of the uterus that opens into the vagina) 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

Usually, abnormal mucus causes infertility only if the abnormal mucus causes chronic cervicitis or if the cervix has been narrowed by treatment for a precancerous abnormality of the cervix (cervical dysplasia).

Did You Know...

  • Just before an egg is released (ovulation), mucus in the cervix changes consistency to allow sperm to enter the uterus.


Doctors examine women to see whether the cervix is narrow and to check for infection.

Tests to determine whether the mucus promotes sperm destruction are rarely used because these tests do not accurately predict the chances of pregnancy.


Treatment may include placing semen directly in the uterus to bypass the mucus (intrauterine insemination). Drugs to thin the mucus, such as guaifenesin, may be used. However, there is no proof that either treatment increases the chances of pregnancy.

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