What are the stages of endometriosis?

Endometriosis is a chronic and progressive disease, which means that over time symptoms They can become more severe and cause complications, especially if left untreated. To make an accurate diagnosis and plan treatment, doctors often use endometriosis staging systems. You'll find a description of the two most effective and commonly used systems in this article. However, remember not to interpret them independently, whether you suspect the condition or have already been diagnosed. The information you're about to read should be considered only as a guide, suggestion, or starting point for a discussion with your doctor. 

Stages of endometriosis - ASRM classification

Endometriosis is a disease about which we still know relatively little. Recently, awareness of the condition has increased significantly among both patients and physicians. Unfortunately, the diagnostic and therapeutic process remains difficult, demanding, and time-consuming. Over the years, experts have strived to create a uniform and universal system for classifying the severity of endometriosis, which would allow for better treatment planning for patients. Unfortunately, despite numerous attempts, each system created to date has been subject to a certain risk of error, which is why there is no single, universally accepted classification of endometriosis stages. However, the most well-known and most frequently used classification is that of the American Society for Reproductive Medicine (ASRM). According to guidelines, endometriosis is classified into four stages based on the size and location of lesions. This assessment is performed during laparoscopic surgery.

Stage 1 endometriosis (minimal)

It is characterized by the presence of small lesions in the uterus, ovaries, fallopian tubes and peritoneum.

Stage 2 endometriosis (mild)

Endometriosis lesions are more extensive, and endometrial (chocolate) cysts may also develop on the ovaries. Additionally, changes in the rectouterine pouch may occur.

Stage 3 endometriosis (moderate)

This stage is characterized by the presence of extensive adhesions and the involvement of the uterosacral ligament. 

Stage 4 (severe) endometriosis

Adhesions are so numerous that they cause organ deformation, decreased mobility and retroverted uterus, and superficial endometrial foci also occur in other structures, such as the bladder, vagina, intestines, and cervix. 

ASRM Classification – Advantages

The advantages of the ASRM classification system are that it is used worldwide, is easy to use, and allows physicians to clearly and simply explain the severity of endometriosis to their patients. Unfortunately, it also has its drawbacks. Diagnostics Scientific evidence and clinical observations show that pain intensity and fertility problems do not correlate with the ASRM endometriosis stage. This means that patients with stage IV endometriosis do not necessarily report more severe pain symptoms than patients with stage I disease. The biggest caveat, however, is that the ASRM classification does not account for the presence of deeply infiltrating endometriosis in sites such as the uterosacral ligaments, bladder, vagina, and bowel. Therefore, the ENZIAN classification was developed to complement this classification.

Stages of endometriosis – ENZIAN classification

The ENZIAN classification was first introduced in 2005 and subsequently revised in 2010 and 2011. It allows for a better assessment of the stage of deep infiltrating endometriosis, i.e. endometriosis that penetrates the tissues deeper than 5 mm. Thanks to it, deep endometrial lesions and their location can be described more precisely, which facilitates communication between the doctor and the patient, but also between doctors. 

The ENZIAN classification differs from the ASRM because it does not divide endometriosis into specific stages, but uses letters and graphic symbols (pictograms) to mark the sites where endometriotic changes occur. 

For classification purposes, the posterior uterus is conventionally divided into part A, consisting of the rectovaginal septum and vagina; part B, consisting of the uterosacral ligament and pelvic walls; and part C, consisting of the sigmoid colon and rectum. If the lesion is smaller than 1 cm, it is assigned the number 1; if it is between 1 and 3 cm, it is assigned the letter 2; and for even larger lesions, the letter 3. Additionally, the prefix "E" indicates the presence of an endometriotic tumor. The final result is as follows: the number following the prefix indicates the size of the lesion, and the lowercase letter following the number indicates the location. Endometriosis extension to other organs is defined as follows: "FA" is defined as adenomyosis, "FB" as bladder involvement, "FU" as ureteral involvement, "FO" as other organ involvement, and "FI" as bowel involvement. You absolutely don't need to learn or memorize this! Your doctor will explain everything to you. I just wanted to draw your attention to the complexity of the classifications used to assess the stages of endometriosis, to warn you against drawing conclusions on your own, which could cause unnecessary stress. 

If you are looking for a good and experienced doctor, check out our list of recommended specialists. 

Stages of endometriosis – how to approach it in practice?

Endometriosis classification systems are a helpful tool in diagnosis and treatment planning, but they are not sufficient on their own to plan specific treatments, assess the risk of complications, or assess the chances of pregnancy. In addition to classification, your doctor also considers your symptoms, age, the results of other laboratory and imaging tests, and your overall health. Only such a comprehensive approach allows for effective and safe treatment planning. Don't stress out if you've been diagnosed with stage IV endometriosis. This doesn't mean there's nothing left to do. 

If you suspect you have endometriosis and are wondering what the entire diagnostic process looks like, check out our article "How to detect endometriosis? 

Summary

To facilitate communication between doctors and patients, as well as to improve treatment planning, two endometriosis staging systems are currently used: the ASMR and ENZIAN classifications. Each has its advantages and disadvantages and requires specialized and comprehensive analysis. The most severe stage of endometriosis does not necessarily mean that leczenie will be the most difficult, and the chances of pregnancy will be the lowest. Classifications are just a piece of the puzzle, so for your own peace of mind, never analyze them on your own or compare yourself to others. 

Sources

• Pasalic E. Endometriosis: Classification, pathophysiology, and treatment options, https://www.sciencedirect.com/science/article/pii/S0344033823005484?via%3Dihub [accessed: 17/09/2025]
• Lee S. Classification of endometriosis, https://pmc.ncbi.nlm.nih.gov/articles/PMC7787892/ [accessed: 17/09/2025]

• Brosens I. Endometriosis: a life cycle approach? https://pubmed.ncbi.nlm.nih.gov/23500453/ [accessed: 17/09/2025]
• Bazot M. ENDO_STAGE Magnetic Resonance Imaging: Classification to Screen Endometriosis, https://pubmed.ncbi.nlm.nih.gov/35566569/ [accessed: 17/09/2025]