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How common is endometriosis?

And why is it so difficult to get a diagnosis?

by Nicole Telfer, and Jen Bell
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For many reasons, it is difficult to know how common endometriosis is, just as it is difficult for even a single person to get a diagnosis of endometriosis. On average, someone who presents with symptoms of endometriosis goes on average seven years (from three years to eleven years depending on the country) from the onset of symptoms until getting a diagnosis (1). In places where healthcare is government-funded, the wait for a diagnosis can take even longer, compared to healthcare that is self- or insurance-funded (1).

How prevalent is endometriosis?

Research has tried to determine how common endometriosis is. According to the American College of Obstetrician and Gynecologists, endometriosis may affect about 1 in 10 women of reproductive age (2). But studies that try to predict the prevalence of endometriosis have found a wide range, from less than 1 out of 100, up to 15 out of every 100 women of reproductive age (3-5).

In population studies, where data from a large group of people are used to determine how common a disease is within that population, endometriosis has been reported with less prevalence, at around 1-2% of all women (as shown in the UK and Italy) (3,4). The problem with these studies is that they don’t account for people with asymptomatic endometriosis, who wouldn’t know they have the disease.

In attempts to account for asymptomatic cases, other studies have focused on individuals undergoing pelvic surgery (for various reasons). They look at how often endometriosis is found/observed during surgery. In these studies, the prevalence of endometriosis is often found to be much higher than in large-scale population studies. For example, in one study of women in Michigan undergoing hysterectomies, 3 out of 20 were found to have endometriosis (5). Focusing more specifically on people who got a hysterectomy for the reason of chronic pelvic pain, 2 out of 5 were found to have endometriosis during their surgery (5). This shows a large proportion of people with chronic pelvic pain have endometriosis.

Of the people who got a hysterectomy for reasons other than endometriosis or chronic pelvic pain, 1 in 12 had evidence of endometriosis present (5). This is really important, as it demonstrates that not everyone with endometriosis has pelvic pain.

The bias with these studies lies within the populations they focus on. The people studied are usually women attending gynecological clinics or hospitals, which reflects a smaller, less-representative population sample of people who already have gynecological problems, for which they’re seeking care (3).

The struggle to get an endometriosis diagnosis

It’s difficult to know how common endometriosis is, because diagnosis is so complicated.

Symptoms differ greatly
Endometriosis symptoms can differ greatly from person to person. Most people with endometriosis present with pelvic pain and dysmenorrhea (painful menstruation). These symptoms can be can be mistaken for normal menstrual symptoms, especially if they are present from the first period (1,2,6). Transgender and non-binary people affected by endometriosis may find it harder to get a diagnosis and appropriate healthcare.

Other people with endometriosis may have bowel and/or urinary pain as their predominant symptoms. Others may have no physical symptoms at all — up to a quarter of people with endometriosis are asymptomatic (2,7). Women with endometriosis may also be twice as likely to struggle with infertility, a symptom that is noticed only when someone has difficulty becoming pregnant (8). Because of this wide variety of endometriosis presentations, it can take several visits and potentially years for a healthcare provider to refer a patient onwards to a gynecologist or secondary care specialist to receive a diagnosis (6).

Another reason for delayed diagnosis is likely due to hormonal symptom suppression. When the reproductive hormones stop cycling because of pregnancy, breastfeeding, or use of hormonal contraceptives, pain symptoms may temporarily stop, and a person with endometriosis may not seek medical help (6). Hormonal contraceptives are often prescribed to decrease and regulate menstrual pain and excessive menstrual bleeding, as well as a treatment for endometriosis symptoms. When cycling resumes, symptoms can reoccur.

Diagnosis requires surgery
Getting a diagnosis currently requires a surgical procedure, to confirm that endometriosis-like tissue is visible outside of the uterus. Diagnosis often also requires a biopsy (tissue sample) for confirmation (2). Undergoing surgery to achieve a diagnosis is not something that usually happens immediately, as this is expensive, time-consuming, and like every surgical procedure, carries risks. Researchers are trying to find other ways of diagnosing endometriosis without a surgical procedure. Some of these could include examining the cellular components of menstrual fluid, and differences in menstrual blood-derived stem cells (9,10). More research is needed here.

Even when a healthcare provider feels confident enough to refer a patient to get laparoscopic surgical investigation, the next problem is actually finding and locating the endometrial-like tissue. Endometrial-like tissue can present in many places within the pelvis, such as on the ovaries, behind the uterus, on the peritoneum (the membrane that lines the abdomen and pelvis), in the fallopian tubes, and along the bowels, amongst other places. It can be difficult to locate these endometrial-like lesions. There is also evidence to suggest that perhaps these lesions may change over time or may be difficult to relocate—in some reported cases, lesions found in one surgery could not be located in a later surgery (5).

All of these factors of access, differing symptoms, symptom suppression, and difficulty finding a conclusive diagnosis contribute to why it can be so difficult to accurately determine how many people actually have endometriosis.

Is endometriosis more common in certain populations?

Endometriosis is diagnosed at different rates around the world, which could reflect differing access to healthcare, as well as different rates of the disease across populations. Research suggests that white women are more likely to be diagnosed with the disease, while black and Latina/Hispanic women are least likely to be diagnosed. In the United States, data from a large population study published in 2004 found that women identified as African-American and Hispanic were diagnosed with endometriosis at a 40% lower rate than women identified as Caucasian (11). It’s unknown whether this reflects lower rates of the illness, or is related to the discrimination experienced by women of color in the U.S. healthcare system, from inadequate access to healthcare to racial bias in pain treatment (12-14).

There may be a genetic link to endometriosis. Studies show that identical twins (monozygotic twins) are more likely than non-identical twins (dizygotic twins) to have endometriosis (15,16). Other research has found a 5 to 10 times increase in risk of having endometriosis if a person’s first degree relative (like a mother or a sister) was also diagnosed with the disease (17-18).

Weight may have an influence on endometriosis, as people with high body mass indexes (BMIs) may be less likely to be diagnosed with endometriosis (3,11). Research also shows that people with lower BMI (lower weight) may be more likely to present with endometriosis symptoms (20).

More research, awareness, and access to diagnosis and treatment is needed world-wide to better determine the prevalence of endometriosis.

Think you might have endometriosis symptoms?

If you have painful periods and pelvic pain, see your healthcare provider and let them know if you think something is wrong. For more information, read in detail about endometriosis symptoms, diagnosis and treatment.

Whether you are trying to get a diagnosis or to access appropriate medical care, there are endometriosis support organizations around the world who are there to help. If you’re looking for a trans-friendly OB/GYN you can find some tips in this guide.

Download Clue to track pain, bleeding, and other symptoms. This information that may help with diagnosis and in forming a management plan.

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Surgical instruments pointing inwards forming a circle around a piece of endometrial-like tissue


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