Endometriosis is staged using a point-based scoring system that tallies the location, depth, and size of tissue growths found during surgery or, increasingly, through specialized imaging. The most widely used system, developed by the American Society for Reproductive Medicine (ASRM), assigns a score from 1 to over 40 and places the disease into one of four stages. But staging endometriosis is more complex than a single number, and several classification systems now exist because no single one captures everything a patient and their care team need to know.
The ASRM Point System
The ASRM revised classification is the standard most gynecologists use. During a laparoscopy, the surgeon makes a small incision in the abdomen and inserts a thin tube with a camera to directly visualize the pelvic organs. They then score what they find based on where tissue is growing, how deep it penetrates, and whether organs are stuck together with scar-like bands called adhesions. Each finding adds points to a running total.
Points are assigned for implants on the peritoneum (the lining of the pelvic cavity), on or near the ovaries, and in the space between the uterus and rectum. Shallow, surface-level implants score lower than deep ones. Small adhesions score lower than thick, dense ones that bind organs together. Ovarian cysts filled with old blood, called endometriomas, add significant points depending on their size.
The total determines the stage:
- Stage I (Minimal), 1 to 5 points: A few superficial implants, typically scattered across the pelvic lining with no significant adhesions.
- Stage II (Mild), 6 to 15 points: More implants, some of which may be deeper, but still relatively limited in scope.
- Stage III (Moderate), 16 to 40 points: Deep implants, possible endometriomas on one or both ovaries, and moderate adhesions pulling structures out of their normal position.
- Stage IV (Severe), over 40 points: Many deep implants, large ovarian cysts, and dense adhesions. In extreme cases, organs can become so tightly bound together that surgeons describe it as a “frozen pelvis.”
Why Stage Doesn’t Always Match Symptoms
One of the most frustrating realities of endometriosis staging is that the number on paper often has little to do with how much pain you experience. Research looking at the correlation between pain severity and disease stage found a strong link only at the extremes: stage IV disease correlated with severe pain. But moderate pain showed no meaningful correlation with any particular stage, and milder forms of pain actually had a negative correlation with advanced disease. In plain terms, someone with stage I can be in debilitating pain while someone with stage IV may have fewer pain symptoms.
This happens because pain depends heavily on where implants sit, not just how many there are. A single small implant pressing on a nerve or deeply embedded in the wall between the rectum and vagina can cause far more pain than a large endometrioma on the ovary. The ASRM system was originally designed to predict fertility outcomes, not pain, which is why it can feel disconnected from your lived experience.
The ENZIAN System for Deep Disease
Because the ASRM scoring system doesn’t capture deep-infiltrating endometriosis very well, a newer classification called ENZIAN (now updated as #Enzian) was developed to fill the gap. Rather than assigning a single stage, ENZIAN maps the disease across specific anatomical locations using a letter-and-number code. Each letter represents a body site, and a number beside it indicates the size of the lesion at that location.
The locations tracked include the peritoneum (P), ovaries (O), fallopian tubes (T), the rectovaginal septum (A), pelvic sidewalls (B), rectum (C), other parts of the intestines (FI), the ureters (FU), and the uterine wall itself when adenomyosis is present (FA). It even allows documentation of rare locations like the diaphragm. This makes ENZIAN particularly useful for deep disease that extends beyond the surface of pelvic organs into the bowel wall, bladder, or other structures where surgical planning requires precise mapping.
Your report might use ASRM staging, ENZIAN mapping, or both. Many specialists now combine them to get a more complete picture.
Imaging Before Surgery
Staging has traditionally required surgery, but specialized ultrasound and MRI can now identify many forms of endometriosis without an operation. These imaging tools don’t replace the ASRM point system (which still requires direct visualization), but they help map disease before a surgeon goes in, and in some cases they can guide treatment decisions without surgery at all.
On ultrasound, endometriotic implants appear as dark, spiky nodules that tether nearby structures together. The examiner presses the probe against the pelvis and watches whether organs slide freely past each other. If they don’t, that restricted movement signals adhesions. Endometriomas show up as ovarian cysts filled with uniform, low-level echoes, a pattern sometimes called “ground glass” because of its characteristic appearance. Bowel implants appear as solid, dark nodules with irregular edges growing into the intestinal wall, sometimes taking on a C-shape when they extend through the full thickness.
MRI picks up similar findings with different visual signatures. Deep implants appear as dark, spiky masses on certain scan sequences, sometimes with bright spots indicating trapped blood or glandular tissue. Endometriomas on the rectosigmoid colon often take on a mushroom-cap shape, growing inward from the outer bowel surface toward the interior. Superficial endometriosis is harder to catch on MRI but can sometimes be seen as tiny bright spots or nonspecific thickening on the pelvic lining. Both imaging methods are highly accurate for endometriomas and deep disease, though small, flat implants on the peritoneal surface still frequently escape detection.
The Endometriosis Fertility Index
If you’re trying to conceive, your surgeon may calculate an Endometriosis Fertility Index (EFI) in addition to an ASRM stage. The EFI was designed specifically to predict your chances of getting pregnant without IVF after endometriosis surgery. It combines surgical findings with your personal history, including age, how long you’ve been trying to conceive, and whether you’ve been pregnant before.
A key component is the “least function score,” which evaluates how well each fallopian tube, its fringed opening (the fimbria), and each ovary are working after surgery. The surgeon scores the function of these structures on both sides, and the lowest-scoring side drives part of the final calculation. The resulting EFI score, ranging from 0 to 10, gives a practical estimate of your pregnancy likelihood over the next few years. Higher scores offer reassurance that natural conception is realistic, while lower scores help identify when moving to fertility treatments sooner makes more sense than continuing to wait.
How Staging Guides Treatment
The stage itself doesn’t dictate a single treatment path, but it shapes the conversation. Lower-stage disease with pain as the primary concern is often managed with hormonal medications or a targeted laparoscopic surgery to remove visible implants. The goal at this point is symptom relief and preventing progression.
Higher-stage disease, particularly stage III or IV with large endometriomas, dense adhesions, or deep bowel involvement, typically calls for more extensive surgery. These operations may require a multidisciplinary team that includes a colorectal surgeon or urologist if disease has grown into the intestines or near the ureters. The ENZIAN mapping becomes especially valuable here because it tells the surgical team exactly which structures are involved and how deeply, allowing them to plan the operation in advance rather than discovering problems on the table.
Staging also sets expectations. A stage IV diagnosis with a low EFI score, for example, signals that fertility treatment should be pursued promptly rather than waiting to see if natural conception occurs. A stage I diagnosis in someone with severe pain redirects attention away from the staging number itself and toward the specific locations of implants and the type of pain they’re causing. In every case, the stage is a starting point for planning, not a verdict on outcomes.