Updated March 09, 2015.

Endometriosis is a condition where endometrium, tissue from the lining of the uterus, forms and grows in places outside the uterus. These growths may lead to pain and infertility. Up to 50% of women who have endometriosis may experience infertility.

• Take an Endometriosis Symptoms Quiz

These lost endometrial cells respond to the body's hormones the same way they would inside the uterus. Normally, the endometrium within the uterus thickens to prepare for an embryo.

When pregnancy doesn't occur, the extra lining breaks down and is shed during menstruation. (Learn more about how the female reproductive system works.)

With endometriosis, the endometrial tissue that is outside the uterus also thickens, breaks down, and bleeds, except it can't be expelled vaginally like normal endometrial tissue. Instead, the endometrial tissue outside the uterus builds up over time and forms patches, scar tissue, cysts, and adhesions.

Usually, these endometrial growths form in the pelvic region, including on or near the ovaries, but they can also appear less commonly near the rectum, vagina, fallopian tubes, or even in the urinary or gastrointestinal tracts. More rarely, they can form far away from the pelvic area, including in the lungs, arms, or thighs.

Besides infertility, some women with endometriosis deal with painful periods and painful sexual intercourse, among other symptoms. Other women experience no symptoms and discover the endometriosis only after an infertility evaluation.

• 9 Warning Signs You Shouldn't Ignore: Endometriosis Symptoms

How Does Endometriosis Cause Infertility?

Endometriosis is thought to be involved in 30% of infertility cases, and between 30 to 50% of women with endometriosis experience infertility. Not every woman with endometriosis will have trouble conceiving, and ironically, pregnancy may help with the symptoms and development of the disease.

The connection between infertility and endometriosis isn't completely understood. Even when there's no obvious barrier to fertilization, and the number of implants are small or not blocking the egg or sperm from meeting, infertility can still result.

That said, here are some of the ways endometriosis may affect fertility:

• Endometrial growths, scar tissue, adhesions, or cysts that are around the ovaries may prevent an egg from entering the fallopian tubes.
• Endometrial tissue, if in the ovary, may actually prevent ovulation from occurring.
• Endometriosis may form inside the fallopian tubes, blocking passage inside the tubes and preventing the egg and sperm from meeting.
• Some researchers say that whatever causes endometriosis may also cause infertility. (The cause of endometriosis is not known, but some suspect it's related to a problem with the body's immune system.)
• According to some researchers, women with endometriosis have low levels of a certain substance that helps a fertilized embryo implant itself into the uterine lining.
• Endometriosis can make sexual intercourse painful for some women, and this pain may be more acute around the time of ovulation. Not having sexual intercourse around the time of ovulation would definitely interfere with your ability to get pregnant.

How Is Endometriosis Diagnosed?

The only way to confirm a diagnosis of endometriosis is with diagnostic laparoscopic surgery. This is an outpatient procedure that involves making a small incision in the abdomen, through which the surgeon inserts a tube with a special camera and, if needed, small surgical instruments.

• All About Laparoscopic Surgery for Infertility

To diagnose endometriosis, the surgeon will look for visual evidence of endometrial growths. If found, a biopsy of the tissue may also be performed to confirm things. The doctor should also use the surgery to evaluate the severity of the endometriosis (known as staging).

In mild to moderate cases, the doctor may even treat the endometriosis during the diagnosis surgery.

While laparoscopic surgery is the only way to confirm endometriosis, your doctor may order other tests including ultrasound, MRI, or CT scan to investigate cysts or other reasons for pelvic pain or infertility.

How Is Endometriosis Treated?

Treatment of endometriosis will depend on the severity of the disease, if you're experiencing pain, your age, and on whether you want to get pregnant. Some treatments for endometriosis would lead to decreased fertility, which would not be an option if you're trying to conceive.

Some of the options for treatment if you're trying to conceive include:

• Laparoscopic surgery to remove endometrial growths, scar tissue, and adhesions caused by the endometriosis. This is not a cure, and endometriosis may return later. However, some women will have increased fertility for up to 9 months after surgery.
• IVF treatment, sometimes performed after surgery to remove endometrial growths, but sometimes done without surgical treatment.
• In mild to moderate cases, IUI treatment along with fertility drugs may be used.
• The pain of endometriosis may be treated with over-the-counter pain medications, acupuncture and lifestyle changes, such as regular exercise and diet changes. Surgery to remove endometrial growths is also an option in treating the pain of endometriosis.

If you do not want to get pregnant, treatment options may also include hormonal treatments (which stop ovulation and prevent pregnancy) or, in cases of severe endometriosis, hysterectomy.

Hysterectomy, which involves removing the uterus alone or sometimes along with the ovaries, is considered a treatment of last resort. You can't get pregnant after hysterectomy.

More on causes of infertility:

• Anovulation and Irregular Ovulation
• PCOS Symptoms and Treatment
• Quiz: Do I Have Pelvic Inflammatory Disease (PID) Symptoms?
• Getting Pregnant After 35
• What Are Your Chances for Conceiving After 40?
• Male Infertility Symptoms and Treatment
• Blocked Fallopian Tubes: Symptoms and Treatments

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<sub>Sources:

Endometriosis. A.D.A.M. Healthcare Center. Accessed March 18, 2009. 

Endometriosis: A Guide for Patients. American Society of Reproductive Medicine. Accessed March 18, 2009. http://asrm.org/uploadedFiles/ASRM_Content/Resources/Patient_Resources/Fact_Sheets_and_Info_Booklets/endometriosis.pdf</sub>