What Are the Stages of Endometriosis?

Endometriosis is a very painful condition where tissue that normally grows on the inside of the uterus—in the area called the endometrium—grows outside of it. These tissue growths are called endometrial implants, areas of endometrial tissue found in abnormal locations. Endometriosis is classified into four stages based on the number of endometrial implants, the depth of those implants, and whether there is scaring and ovarian cysts. These stages do not necessarily reflect the level of pain a person experiences or the presence of specific symptoms.

The American Society of Reproductive Medicine classifies the stages of endometriosis based on a point system that gives a numerical scale to the disease. A score of five points or less—or Stage I—indicates a minimal disease. Anything from six points to 15 points—or Stage II—is mild disease. Anything 16 points or more falls in Stages III and IV and indicates a moderate to severe disease.

Diagnosing Endometriosis

Endometriosis affects 10% to 15% of women of reproductive age and 70% of women who have chronic pelvic pain. It can take anywhere from four to 11 years after the onset of symptoms for an official diagnosis of endometriosis to be made. Because pain can be caused by numerous health conditions, diagnosis of endometriosis is usually made by exclusion.  

When a doctor suspects endometriosis, visual confirmation is made with laparoscopy, a surgical procedure using a fiber-optic instrument inserted in the abdominal wall. During the laparoscopy, the doctor will make a small incision in the abdomen and insert a thin tube with a light and camera to view the pelvic region. If signs of endometriosis are seen—such as implanted endometrial tissue or scar tissue—a diagnosis can be made, and any cysts and scar tissue can be removed.

Being able to see scaring and implanted endometrial tissue helps your doctor to classify the disease into different stages. Points are assigned from what is seen in the laparoscopy and, based on these points, endometriosis is classified into four different stages.

The point system for Stage I is one to five points. In this instance, endometriosis is considered minimal. Endometrial implants are few in number, small, and low in depth. Implants may be found on the organs or tissue linings of the pelvis and abdomen. There is minimal or no scar tissue.

Stage II is considered mild disease and falls between six and 15 points. There are more implants than in Stage I. Those implants are deeper and there might be scar tissue. In this stage, there usually isn’t any inflammation. 

Treatment in the first two stages can help with making lesions smaller or getting rid of them altogether. 

Stage III is classified as moderate disease and falls between 16 and 40 points. In this case, there many deep endometrial implants and endometrial cysts in at least one of the ovaries. Called ovarian endometriomas, these cysts form when endometrial tissue attaches to an ovary. The tissue will shed causing blood and tissue to collect and turn brown. For this reason, ovarian endometriomas are also called chocolate cysts.

Your doctor may also find filmy adhesions during the laparoscopy. These thin bands of tissue are scar tissue form because the body is trying to respond and protect itself against the inflammation caused by endometriosis. These adhesions will cause the organs to stick together in the wrong places. They are also known for causing sharp, stabbing pain, and nausea in women with endometriosis. 

Stage IV is the most severe stage of endometriosis and is usually given more than 40 points. This is because there are a large number of cysts and severe adhesions.

In this stage, an endometrioma can be as large as a grapefruit and will need to be surgically removed. There will also be smaller cysts on the back wall of the uterus and rectum.

Some women in this stage may experience digestive issues, including painful bowel movements, abdominal pain, constipation, nausea, and vomiting. Additionally, both Fallopian tubes may be blocked from scarring resulting in infertility.

Treating endometriosis during this late stage can be difficult and doctors will need to rely on surgical intervention to treat women who have reached this stage.

Most people think the severity of stages in endometriosis is determined similarly to cancer stages, where cancer starts in one part of the body and spreads to distant organs. However, endometriosis doesn’t spread or grow like cancer.

In fact, the disease can be widespread as early as Stage I or II. Moreover, these stages don’t determine fertility issues. Further, they don’t tell you how much pain a woman is experiencing or how her quality of life is affected.   

Experts don’t know why some women have more severe cases and symptoms of endometriosis. Also, the condition doesn't always go from one stage to the next. If left untreated, it can either remain the same, get worse, or even get better.

Additionally, these stages don’t really give doctors much guidance in treating endometriosis as each woman with this condition is unique.

A Word From Verywell

Endometriosis has no cure, but it does not mean it has to negatively impact the daily lives of those affected. There are effective treatments for managing pain and treating fertility issues, including medications, hormone therapy, and surgery. Researchers are continually investigating new and improved treatment approaches. And for many women, symptoms may improve after menopause.