Women who are underweight are more likely to develop endometriosis, but recent research suggests that obese women with the condition are more likely to have severe symptoms.

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About 176 million women worldwide (10 percent of women in the United States) are believed to suffer from endometriosis, which typically strikes during a woman’s reproductive years. But despite the fact endometriosis can cause severe physical pain, depression, and infertility, statistics on endometriosis from the National Institutes of Health suggest that it can take as long as a decade for some women to be diagnosed with the condition.

What Is Endometriosis?

Endometriosis is a condition in which the endometrium (the tissue that lines the uterus) spreads outside of the uterus and grows elsewhere in the abdomen, forming lesions that can affect the ovaries, fallopian tubes, the peritoneum (the membrane that covers the abdominal organs), the bladder, and intestines. In rare cases, endometriosis can cause endometrial tissue to spread as far as the spine, lungs and brain.

What Causes Endometriosis?

It’s not clear what causes endometriosis. Some experts have posited that the condition is caused by a reversal in the flow of menstrual blood that causes it to flow through the fallopian tubes and out into the abdomen. The theory is that endometrial cells within menstrual blood attach to other organs in the pelvic cavity and grow—however, research suggests that most women with retrograde flow do not develop endometriosis. Other experts have suggested that endometriosis is caused by estrogen causing cells in the peritoneum to spontaneously transform into endometrial cells.

It’s also possible that endometrial cells are transported elsewhere in the body via the blood vessels or the lymphatic system, which would explain how endometriosis can develop in areas of the body that are not in the immediate vicinity of the uterus. Some experts contend that endometriosis may be an autoimmune disorder, and recent research indicates that there may be be a genetic tendency to endometriosis.

Endometriosis Symptoms

As part of the menstrual cycle, the endometrium thickens in preparation for a fertilized egg to implant in the uterus. If conception does not take place, the endometrium breaks down and is shed—this is what constitutes a woman’s menstrual period. During menstruation, some women experience cramping, low back pain, and other symptoms. These symptoms have implications for women with endometriosis since endometrial tissue that has implanted elsewhere in the body behaves in the same way as endometrial tissue in the uterus: becoming thicker, before breaking down and then causing bleeding as it sheds.

Most women with endometriosis suffer the same cramping pain in areas where endometrial tissue is growing as they do during their period. But the pain can occur independently of actual menstruation as well as during it, and often is more severe than menstrual cramping. During the menstrual cycle, shed tissue is able to exit the body—however, endometrial tissue in other parts of the body has no exit route. Instead, it is trapped, causing irritation in the surrounding area, and leading to the hallmark of endometriosis: cysts and bands of scar tissue that are known as adhesions because they can cause pelvic organs to stick to each other.

Women with endometriosis also report painful intercourse, pain when they urinate and/or pass a bowel movement, “breakthrough” bleeding in between their menstrual periods, and very heavy periods.

Who Is Most At Risk for Endometriosis?

Women who are underweight are more likely to develop endometriosis, but recent research (Journal of Endometriosis and Pelvic Pain Disorders, May 27, 2018) suggests that obese women with the condition are more likely to have severe symptoms. In the study, the pain scores of obese women with endometriosis were twice as high as pain scores in under- and normal-weight women.

Other factors that raise the risk of endometriosis include early menstruation, a menstrual cycle that is shorter than the average 28 days, never having given birth, later than usual menopause, having a first-degree relative (mother, sister, aunt) with endometriosis, consuming excessive amounts of alcohol and/or coffee, since these can raise estrogen levels, lack of exercise, and structural abnormalities of the uterus that prevent menstrual blood from exiting.

Conversely, breastfeeding seems to have a protective effect against endometriosis particularly in women who breastfeed for longer than average, according to a study (British Medical Journal, August 27, 2017) that tracked thousands of women for more than two decades. During the study period, 3,296 women were diagnosed with endometriosis after their first pregnancy. The data showed that for every three additional months that the women breastfed per pregnancy they experienced an 8 percent drop in their risk of endometriosis. Women who exclusively breastfed (without giving their babies additional formula milk) had a 14 percent lower risk of endometriosis for every three additional months of exclusive breastfeeding. Overall, women who exclusively breastfed all of their children for 18 months or more across their reproductive lifetime had a nearly 30 percent lower risk of endometriosis. The fact that breastfeeding temporarily prevents menstruation is thought to account for some of the benefits of breastfeeding, but the researchers say other mechanisms were likely at work too.

Endometriosis Complications

About half of women with endometriosis experience difficulty conceiving (in fact, the condition is usually diagnosed when women seek medical assistance with their fertility problems), but up to 70 percent of them do manage to get pregnant. Unfortunately, they are at at greater risk of miscarriage and ectopic pregnancy if they do conceive. A large 2015 study found that women with endometriosis had a 76 percent greater risk for miscarriage than women without the condition, as well as a nearly three-times-greater risk for ectopic pregnancy (in which the fertilized egg implants in the fallopian tube). The researchers also found that women with endometriosis who successfully progressed beyond week 24 of their pregnancy were at greater risk of hemorrhage (both before and after labor) and preterm labor.

Ovarian cancer is also more likely to occur in women with endometriosis. Also, while endometriosis symptoms typically ease after menopause they may persist in women who take hormone replacement therapy to alleviate menopausal symptoms, such as hot flashes.

Diagnosing and Treating Endometriosis

Many women are diagnosed with endometriosis on the strength of their symptoms alone, but only ultrasound and laparoscopy can provide a definitive diagnosis since these methods are able to visualize endometrial tissue growing outside of the uterus.

The symptoms can sometimes be managed by taking contraceptives and other drugs that lower estrogen levels and shrink endometrial tissue growing outside of the uterus. However, the latter cause early menopause and menopausal symptoms, as well as loss of bone density (These can be reversed if you stop taking the drugs).

Surgery is also an option to treat endometriosis, particularly for women who are having trouble conceiving due to the condition. The surgery can be carried out using a keyhole approach but if endometrial tissue has spread extensively, open surgery may be necessary to remove rogue endometrial tissue. Women who continue to have difficulty conceiving after surgery may be advised to try assisted reproductive methods.

The most extreme surgical approach to treating endometriosis is a hysterectomy to remove the uterus, but this should be considered a last resort, particularly for women of childbearing age.