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Doctors don't know exactly how endometriosis can keep you from getting pregnant. But there are some theories.

To read more about the causes and treatment of infertility, see our articles on infertility.

If you have endometriosis, the patches of tissue outside your womb bleed every month when you get your period. This bleeding can damage your fallopian tubes or your ovaries. They may stick together and they may stop working properly. If this happens, you may find it harder to get pregnant.

Some people who have endometriosis get pain when they have sex. So they might have sex less often. Less sex means a lower chance of getting pregnant. If you're trying to get pregnant, you should have sex at least two or three times every week.¹

We know that if you have severe endometriosis, it lowers your chance of getting pregnant. Doctors think that mild endometriosis can also make it harder for you to get pregnant, but there's no proof. (See Stages of endometriosis.)

About a quarter of women who have tests for infertility have some kind of endometriosis.^{2 3 4} And many of these women have only mild endometriosis.

Mild endometriosis may stop your ovaries from working properly. But we don't know exactly how.⁵ It's possible that something else is causing infertility in women with mild endometriosis.

Bear in mind that the symptoms of endometriosis are very similar to the symptoms of some other illnesses and some of these can affect your chance of getting pregnant. To learn more, see Other illnesses with symptoms like endometriosis.

This information is for educational use only, and is not a substitute for prompt professional medical advice. Readers should always consult a physician or other professional for advice and treatment. ©BMJ Publishing Group Limited 2008. All rights reserved.