What Are the Stages of Endometriosis?

Endometriosis is a painful condition where tissue that is similar (but not identical) to the kind inside the uterus (endometrium) grows outside of it.

These abnormal tissue growths (endometrial implants or lesions) can be located throughout the body, but tend to be found on or near the reproductive organs.

The most common sites are the ovaries, the fallopian tubes, and the cul de sac behind the uterus. Implants may also be found in the nearby urinary tract and bowel.

Endometriosis is classified into one of four stages. The stage is determined based on the number of endometrial implants, how deep the implants are, and whether cysts or scarring are present.

It's important to note the stage does not necessarily reflect the level of pain or specific symptoms a person with endometriosis experiences.

Determining Stages of Endometriosis

The most common method is a points rating and numerical scale system created by the American Society of Reproductive Medicine (ASRM), which determines disease stages by assigning points according to characteristics of the disease. 

ASRM's scale has four stages:

Stage I: Minimal disease (five points or less)

Stage II: Mild disease (six to 15 points)

Stages III and IV: Moderate to severe disease (16 points and higher)

In addition to the current scale, researchers are also working on new methods to evaluate and stage endometriosis.

Diagnosing Endometriosis

While exact numbers are not known, global statistics have shown that one in 10 women of reproductive age have endometriosis.

The condition is primarily diagnosed in people who identify as female, but it is not exclusive to them. Transgender men and people who are gender non-conforming can also have endometriosis. While rare, lesions have been found in cisgender men receiving estrogen therapy to treat prostate cancer or after surgery to repair inguinal hernias.

Diagnosing endometriosis can be challenging, in part because many common symptoms, such as pelvic and abdominal pain, can be caused by other health conditions. However, around 70% of women with chronic pelvic pain are found to have endometriosis. 

There are also other reasons diagnosing endometriosis is challenging: For example, unless endometriosis is advanced and has caused other issues with organs and structures (such as ovarian cysts) it typically doesn't show up on diagnostic imaging tests such as a CT scan or ultrasound.

If a doctor suspects endometriosis, the only way to confirm the diagnosis is to do a surgery to look inside the pelvis and abdomen (visual confirmation) and take a sample of tissue (biopsy) to look at under a microscope.

During a diagnostic laparoscopy (a surgical procedure using a fiber-optic instrument inserted in the abdominal wall) ta surgeon makes a small incision in the abdomen. They insert a thin tube with a light and camera through the incision to see inside the pelvic and abdominal cavity.

If implanted endometrial tissue, scar tissue, cysts, adhesions, or other indications of endometriosis are seen, a surgeon may be able to make the diagnosis visually and take a tissue sample to confirm. Points are assigned based on the characteristics of the endometrial lesions to determine the stage of the disease.

However, it's important to know that surgeons who are not specially-trained may not recognize endometriosis lesions, or that the lesions may not be visible to the naked eye at all.

Depending on the stage of the disease, lesions can vary in appearance, color, and depth. Even using surgical lighting and scopes, surgeons may not be able to see lesions that are superficial and clear, for example.

Stage I

Stage I or "minimal" endometriosis scores one to five points. At this stage, endometrial implants are few in number, small, and superficial. 

The implants may be found on organs or the tissue that lines the pelvis and abdominal cavity. Scar tissue is not present or is minimal.

Stage II

Stage II or "mild disease" scores between six and 15 points. At this stage, there are more implants, and they are deeper than in Stage I. There can be scar tissue at this stage, but not be signs of active inflammation.

Stage III

Stage III or "moderate disease" has between 16 and 40 points. At this stage, there are many deep endometrial implants and endometrial cysts in at least one of the ovaries. 

These cysts, called ovarian endometriomas, form when endometrial tissue attaches to an ovary. As the tissue sheds, it collects along with old, thick, brown blood.

Based on the appearance of the blood, ovarian endometriomas are sometimes called "chocolate cysts."

At this stage, filmy adhesions may be present. These thin bands of scar tissue form in response to the body's attempts to protect itself from the inflammation caused by endometriosis.

Adhesions tend to make organs to stick together, which can cause sharp, stabbing pain, as well as other symptoms depending on their location.

For example, when on the reproductive organs, adhesions contribute to subfertility and can make it harder for someone to get pregnant.

Adhesions on the bowel may lead to gastrointestinal symptoms, such as nausea.

People with endometriosis can develop adhesions from the disease as well as the surgeries used to diagnose and treat it.

Stage IV

Stage IV is the most severe stage of endometriosis, typically accruing over 40 points. At this stage, a large number of cysts and severe adhesions are present.

While some types of cysts go away on their own, the cysts that form as a result of endometriosis usually need to be surgically removed. Endometriomas can grow to be quite large; even as big as a grapefruit.

Small cysts on the back wall of the uterus and rectum may also be found at this stage. People with endometriosis in these areas may experience painful bowel movements, abdominal pain, constipation, nausea, and vomiting.

If endometrial lesions, cysts, or scar tissue is blocking one or both fallopian tubes, a person with endometriosis may experience infertility. Sometimes, trouble conceiving is the only symptom of endometriosis a person has.

Treating severe endometriosis is difficult. Even if a surgeon makes the diagnosis, they may not be familiar with or have experience using the surgical techniques for removing the lesions.

While there are non-surgical ways to treat endometriosis (including hormonal birth control and other medications) the "gold standard" treatment is a highly-specialized procedure called excision surgery.

To manage endometriosis, someone might need to use more than one form of treatment. Sometimes, multiple surgeries are needed to treat the disease and control pain.

If you are diagnosed with endometriosis, it can be helpful to get a referral to an endometriosis specialist to discuss your treatment options.

Making Sense of Staging

People often think the stages of endometriosis are determined similarly to cancer stages, but endometriosis doesn’t spread or grow the same way cancer cells do.

Cancer starts in one part of the body and spreads to distant organs. As cancer progresses, a person usually feels sicker, may have more pain, and has more complications related to the disease.

On the other hand, endometriosis can be widespread even in the early stages, and the disease stage doesn't necessarily correlate with someone's symptoms, pain levels, or complications like digestive problems and fertility issues.

Unlike other diseases that can be staged, endometriosis won't necessarily progress through the stages in a predictable way.

Research has shown that without treatment (particularly if diagnosed during adolescence) endometriosis might improve, get worse, or stay the same.

There is currently no method to predict which outcome a person with the disease will have.

Researchers also aren't sure why some people have severe disease and others do not, or why the stages of endometriosis don't always correspond to the severity of symptoms, pain, and complications a person with the disease experiences.

Further complicating its management, these stages don't offer much guidance for treating endometriosis to medical professionals.

Endometriosis needs to be evaluated on a case-by-case basis, and each patient will need an individualized approach to treating the disease and managing symptoms.

A Word From Verywell

There is no cure for endometriosis and it can be challenging to diagnose. Once the disease is accurately diagnosed and staged, people with endometriosis can discuss the most effective strategies for managing and treating their symptoms.

People may need to use more than one kind of treatment to control pain and resolve other symptoms related to endometriosis. Specialized surgery is recommended for severe endometriosis. In some cases, people may need more than one surgery to treat the disease and the complications it can cause.

People with endometriosis who have pain, digestive problems, infertility, and other symptoms can also try non-surgical treatment strategies, including medications and hormone therapy.