Endometriosis Stages: What Stage 1 to Stage 4 Mean, and What They Do Not

The rASRM stages, I to IV

The rASRM classification, revised in 1996 and published in 1997, assigns points at surgery. Lesions on the peritoneum and on each ovary score by size (under 1 cm, 1 to 3 cm, over 3 cm) and by whether they are superficial or deep. Adhesions (scar tissue) around each ovary and tube score by how dense they are and how much of the organ they wrap. Obliteration of the posterior cul-de-sac, the pocket between the uterus and rectum, adds a large block of points. The total gives the stage.

• Stage I, minimal: 1 to 5 points. A few superficial spots, little or no scar tissue.
• Stage II, mild: 6 to 15 points. More or deeper lesions, filmy adhesions.
• Stage III, moderate: 16 to 40 points. Deep lesions, an endometrioma (ovarian cyst) on one or both ovaries, denser adhesions.
• Stage IV, severe: more than 40 points. Large endometriomas, dense adhesions binding ovaries, tubes and bowel, and often a sealed posterior cul-de-sac.

What the stage does not count

The rASRM system was designed for fertility research. It scores the ovaries and tubes in detail and the rest of the pelvis barely at all. Deep nodules in the uterosacral ligaments, the vagina, the bowel, the bladder and the ureter add few points unless they also seal the cul-de-sac. A woman with a 3 cm bowel nodule and no ovarian disease can be stage II; a woman with two endometriomas and little pain can be stage IV. The World Endometriosis Society consensus (2017) therefore recommended recording the rASRM stage together with the Enzian description for deep disease and the Endometriosis Fertility Index for women trying to conceive.

Reproducibility is another limit. In a 2021 study of 1,224 women at three specialist centers, agreement between rASRM stage and the complexity of the surgery actually performed was kappa 0.317, so two surgeons often assign different stages to the same pelvis (Abrao 2021). A 2025 Australian study of 317 patients likewise noted that rASRM has historically shown poor inter-observer agreement (Mak 2025).

#Enzian: mapping deep endometriosis

The #Enzian classification (Keckstein 2021) came from a European consensus group and describes every type of endometriosis in one map, from imaging or from surgery. Instead of a single number, it records each compartment separately: P for peritoneal lesions, O for the ovaries, T for the tubes and ovaries being stuck down, A for the vagina and the space between rectum and vagina, B for the uterosacral ligaments and the tissue beside the cervix, C for the rectum and sigmoid colon, and F for other sites such as the bladder (FB), the ureter (FU), other bowel (FI) and adenomyosis in the uterine wall (FA). Each lesion is graded 1 to 3 by size: under 1 cm, 1 to 3 cm, or over 3 cm, with left and right sides noted.

A report such as "B2 left, C3" tells the next surgeon, and you, exactly where the disease is and how big it is, which matters more for planning bowel or ureter surgery than "stage IV".

Why stage predicts pain poorly

Pain in endometriosis comes from inflammation, nerve fibers growing into lesions, deep nodules infiltrating nerves, and pelvic floor muscles that tighten in response. A point score built around ovaries and adhesions captures none of this. In the Vercellini study of 1,054 consecutive women having surgery (319 minimal, 139 mild, 292 moderate, 304 severe), stage was linked to pain only weakly: the odds ratio for severe period pain per stage was 1.33, and for non-menstrual pain 1.01, both close to no effect. Lesion location mattered more. Lesions in the posterior cul-de-sac raised the odds of pain with intercourse by 2.64 times (Vercellini 2007).

The AAGL 2021 study found the same pattern: the rASRM stage and the newer AAGL score correlated only modestly, and about equally, with period pain, pain with sex, pain with bowel movements and infertility (Abrao 2021). Stage I disease can be disabling; stage IV disease can be found by chance during fertility surgery.

Why stage predicts fertility poorly too

Stage predicts pregnancy poorly on its own. The Endometriosis Fertility Index (EFI), developed from 579 women and tested in 222 more, predicts the chance of pregnancy without IVF after surgery (Adamson 2010). Its strongest component is the "least function score", a surgeon's rating of how well the tubes, fimbria and ovaries work on each side after surgery. A stage IV woman whose tubes and ovaries still function can have a good EFI. If you are trying to conceive, ask for your EFI, not just your stage.

How staging is determined

Formally, the rASRM stage is assigned at surgery, by what the surgeon sees and touches. In practice, imaging now does much of the work beforehand. Transvaginal ultrasound by a trained operator and pelvic MRI can identify endometriomas, deep nodules behind the uterus and in the bowel or bladder, and signs that the ovaries or cul-de-sac are stuck down. The ESHRE 2022 guideline recommends imaging as part of the workup and no longer requires laparoscopy to make the diagnosis. The #Enzian system records imaging findings in the same language as surgical findings, so a surgeon can plan for deep disease rather than discover it during the operation.

Superficial peritoneal lesions remain invisible on imaging. A normal scan does not rule out stage I or II disease, and NICE guideline NG73 says not to exclude endometriosis when examination, ultrasound or MRI is normal.

What "stage 4 endometriosis" does and does not mean

• It does mean extensive disease: usually large endometriomas, dense adhesions and a sealed posterior cul-de-sac, with surgery more likely to involve the bowel or ureter.
• It does mean surgery should be done by a team experienced in deep endometriosis, often with a colorectal or urologic surgeon available (ESHRE 2022).
• It does not mean cancer. Endometriosis is not cancer; stage describes extent, not malignancy. A small increase in the risk of some ovarian cancers has been reported, but the absolute risk stays low (Zondervan 2020).
• It does not mean the worst pain. Pain depends on where lesions are and whether nerves and muscles are involved, not on the point total.
• It does not mean pregnancy is impossible. Fertility after surgery depends on tubal and ovarian function, which the EFI measures.
• It does not mean the disease marched through stages I to III first. Stage is a snapshot at one operation, not a step on a fixed path.

Questions to ask about your stage

• Which staging system was used, and can I have the written report and photographs?
• Where exactly was the disease? Was anything deep, and was it fully removed, left, or ablated?
• If I want to conceive, what is my Endometriosis Fertility Index?
• Does my stage change the treatment plan, or do my pain and my goals drive it?