Endometriosis is not the same for every patient. It occurs in several different forms depending on the location of endometrial implants, the organs affected, and the severity of symptoms for each patient.

Classifying endometriosis into stages can help healthcare providers to describe the condition and diagnose treatment. Understanding which stage of endometriosis applies to them also helps patients to manage their endometriosis symptoms for a better quality of life. 

What Is Endometriosis?

Endometriosis is a condition in which tissue similar to that which lines the inside of the womb, known as the endometrium, begins to grow outside of the womb (uterus) This misplaced tissue can form lesions, cysts, and adhesions on various pelvic organs. The result is often dull pelvic pain, heavy menstruation, and difficulties becoming pregnant, amongst other symptoms. 

Defining the Stages of Endometriosis

The staging system for endometriosis is outlined by The American Society of Reproductive Medicine (ARSM) to help clarify the extent of each patient’s condition. In addition to aiding diagnosis and treatment options, outlining the four stages of endometriosis is helpful for surgeons when removing endometrial tissue and for research purposes.  

Where Does Endometriosis Grow?

Endometrial-like tissue that grows outside of the uterus is most commonly found on the ovaries, fallopian tubes, peritoneum, and pelvic floor. It can also grow on the bowel, bladder, intestines, and rectum. In rare cases, it has been found growing in the chest area. 

Key Terms Associated with the Stages of Endometriosis

In order to understand the ASRM guidelines that outline the four stages of endometriosis, clarification of the following terms is helpful. 

Endometriosis implants are formations of endometrial-like cells found growing outside of the uterus. 

Endometrial lesions are usually small and flat patches of endometrial-like tissue that grow on organs outside of the uterus. Lesions are known to thicken or become inflamed during the menstrual cycle and bleed during menstruation. However, because this type of tissue does not leave the body as the lining of the uterus does, it can result in pelvic pain. 

Endometrial adhesions are known to form when endometrial implants bleed and inflame the surrounding area, causing a band of tissue to form between two organs. Within the realms of the four stages of endometriosis, adhesions can be referred to as thin, filmy, thick, dense, or opaque. 

Endometriomas are cysts that are most commonly found in the ovaries. Because they are typically filled with dark brown endometrial fluid, they are also referred to as "chocolate cysts." The presence of endometriomas indicates a more severe stage of endometriosis.

The Four Stages of Endometriosis

Although the four stages of endometriosis outlined by the ASRM can clarify the location, scope, and density of endometrial implants, it is important to understand that symptoms and quality of life can still vary for each patient. In other words, patients in stage one could experience symptoms while patients in stage two might not.  

As per the ASRM, the stages of endometriosis are based on a grading system, where points are allocated according to the location, number of endometrial implants, and depth of infiltration on organs. The presence and severity of adhesions and ovarian endometriomas are also factored, and allocated points. Essentially, the higher accumulation of points indicates a more severe stage of endometriosis.

Stage I Endometriosis (1-5 points)

The ASRM describes stage I as minimal endometriosis with few superficial implants. In stage I, endometriosis is typically found on the peritoneum, which is the membrane that lines the abdomen. Because implants or lesions are small and flat at this stage, the points allocated for these small implants would equal no more than 5 on the scaling system. 

Stage II Endometriosis (6-15 points) 

Stage II endometriosis is described as mild, with a larger number of endometrial implants found growing outside of the uterus. Some of these lesions would also be deeper than those identified in stage I meaning they would be designated more points on the scaling system. The points allocated for stage II endometriosis range from six to 15.  

Stage III Endometriosis (16-40 points)

Described as moderate endometriosis, several deep implants are typically identified in stage III. Small ovarian endometriomas are also present, on one or both ovaries. And the presence of thin filmy adhesions on pelvic organs is also usual. Points allocated in stage III endometriosis range from 16 to 40.   

Stage IV Endometriosis

Known as severe endometriosis, stage IV typically reveals many deep endometrial lesions outside of the uterus as well as dense adhesions. In some cases of stage IV endometriosis, adhesions can still be filmy as opposed to dense, and implants could also be superficial, but the point allocation would still rise due to the widespread amount of them. Point allocation higher than 40 indicates severe endometriosis.

Medical research into endometriosis has clarified that it doesn’t always progress from one stage to the next. For some women, endometriosis can worsen over time, but it stays at the same stage for others. Unfortunately, researchers cannot yet explain why. It is also unclear why some women with stage III and IV endometriosis can suffer less intense symptoms than some patients with stage II. 


The American Society of Reproductive Medicine (ASRM) is the most widely used system for defining the four stages of endometriosis. Each stage is classified based on the location, depth, number, and size of endometrial implants growing outside of the uterus.

Understanding their stage of endometriosis can help patients comprehend the extent of their condition and better manage their endometriosis symptoms for a better quality of life. 


American Society for Reproductive Medicine - Revised American Society for Reproductive Medicine classification of endometriosis: 1996, - https://www.fertstert.org/article/S0015-0282(97)81391-X/pdf

Endometriosis Foundation of America - Endometriosis Stages:

Understanding the Different Stages of Endometriosis - https://www.endofound.org/stages-of-endometriosis

Endometriosis Foundation of America - Everything You Need to Know About Pelvic Floor Physical Therapy (PFPT) for Endometriosis - https://www.endofound.org/everything-you-need-to-know-about-pelvic-floor-physical-therapy-pfpt-for-endometriosis

HealthyWomen.org - Lifestyle and Dietary Changes for Endometriosis - https://www.healthywomen.org/content/article/lifestyle-and-dietary-changes-endometriosis


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