Endometriosis Stages and What They Mean

Table of Contents
View All
Table of Contents

In the most commonly used classification system, endometriosis stages are as follows: 1-minimal, 2-mild, 3-moderate, and 4-severe. These reflect the extent of disease, which occurs when tissue that is similar to the kind that lines the uterus (endometrium) grows outside of it.

Specifically, endometriosis stages reflect the number of growths (implants), their depth, and whether cysts or scarring are present.

A woman raising her hand to a computer screen with a healthcare provider

Urbazon / Getty Images

Endometriosis is a painful condition, but endometriosis stages do not necessarily reflect the level of pain or specific symptoms a person experiences.

This article discusses what the four stages of endometriosis mean, how they're diagnosed, and the role of other classification systems.

Endometriosis Staging System

There are different ways to classify the severity of endometriosis. The most common method is a points rating and numerical scale system created by the American Society of Reproductive Medicine (ASRM).

This determines disease stages by assigning points according to characteristics of the disease. 

ASRM's scale has four endometriosis stages:

  • Stage 1: Minimal disease (five points or less)
  • Stage 2: Mild disease (six to 15 points)
  • Stage 3: Moderate disease (16 to 40 points)
  • Stage 4: Severe disease (41 points and higher)

In addition to the current scale, researchers are also working on new methods to evaluate and stage endometriosis.

How Points Are Assigned

Unless endometriosis is advanced and has caused other issues with organs and structures, it typically doesn't show up on diagnostic imaging tests such as a computed tomography (CT) scan or ultrasound.

When endometriosis is suspected, the only way for a healthcare provider to confirm the diagnosis is to do surgery to look inside the pelvis and abdomen.

If indications of endometriosis are seen, a surgeon may be able to make the diagnosis visually. Regardless, they will still take a sample of tissue (biopsy) to look at under a microscope.

Depending on the stage of the disease, lesions can vary in appearance, color, and depth. Even using surgical lighting and scopes, surgeons may not be able to see lesions that are superficial and clear, for example.

Using the ASRM staging system, points are then assigned based on the characteristics of the endometrial lesions to determine the stage of endometriosis.

Stage 1 Endometriosis

Stage 1, or "minimal" endometriosis, is used for cases that:

  • Involve few small and superficial endometrial growths
  • Have growths on organs or the tissue that lines the pelvis and abdominal cavity
  • Show minimal or no scar tissue

Having stage 1 endometriosis doesn't mean a person will have few or no symptoms, or that the disease won't have a major impact on their life.

Stage 2 Endometriosis

Stage 2 endometriosis defines "mild disease." At this stage, there is evidence of:

  • More implants than in stage 1
  • Deeper implants than in stage 1
  • Possible scar tissue, but no signs of active inflammation

Endometriosis implants can be located throughout the body, but tend to be found on or near the ovaries, fallopian tubes, and area behind the uterus.

Stage 3 Endometriosis

Stage 3 endometriosis is for "moderate" disease. At this stage, there are:

  • Many deep endometrial implants
  • Cysts (ovarian endometriomas) in at least one of the ovaries
  • Filmy adhesions (in some cases)

Ovarian endometriomas form when endometrial tissue attaches to an ovary. As the tissue sheds, it collects along with old, thick, brown blood.

Based on the appearance of the blood, ovarian endometriomas are sometimes called "chocolate cysts."

Filmy adhesions are thin bands of scar tissue that form in response to the body's attempts to protect itself from the inflammation caused by endometriosis. (They can also form because of the surgeries used to diagnose and treat it.)

Adhesions tend to make organs to stick together, which can cause sharp, stabbing pain, as well as other symptoms depending on their location. For example, when on the reproductive organs, adhesions can make it harder for someone to get pregnant.

Adhesions on the bowel may lead to gastrointestinal symptoms, such as nausea.

Stage 4 Endometriosis

Stage 4 endometriosis is the most severe. At this stage, there are:

  • A large number of cysts
  • Severe adhesions

While some types of cysts go away on their own, the cysts that form as a result of endometriosis usually need to be surgically removed. They can grow to be quite large, even as big as a grapefruit.

Small cysts on the back wall of the uterus and rectum may also be found at this stage. People with endometriosis in these areas may experience painful bowel movements, abdominal pain, constipation, nausea, and vomiting.

If endometrial lesions, cysts, or scar tissue is blocking one or both fallopian tubes, a person with endometriosis may experience infertility. Sometimes, trouble conceiving is the only symptom of endometriosis a person has.

Other Endometriosis Staging Methods

The endometriosis stages described above are those your healthcare provider will use to describe your disease severity.

There are other endometriosis staging methods that can be used to describe other aspects of the disease, including where lesions are located and the impact on fertility.


The ENZIAN classification system was developed to supplement the ASRM numerical scale system. It classifies deep infiltrating endometriosis based on the location and invasiveness of the lesion.

Unlike the ASRM classification, the ENZIAN score can be determined using imaging, such as magnetic resonance imaging (MRI).

There are eight designations used in the ENZIAN classification system:

  • Compartment A (vagina and rectovaginal septum)
  • Compartment B (uterosacral ligaments and pelvic walls)
  • Compartment C (sigmoid colon and rectum)
  • FA (adenomyosis)
  • FB (involvement of the bladder)
  • FU (intrinsic ureter involvement)
  • FI (intestine)
  • FO (other localizations)

The severity of invasiveness is classified as follows:

  • Grade 1 (less than 1 cm)
  • Grade 2 (1 to 3 cm)
  • Grade 3 (greater than 3 cm)

Endometriosis Fertility Index

The endometriosis fertility index (EFI) was developed to predict the pregnancy rate in patients with surgically diagnosed endometriosis who haven't attempted to become pregnant with in vitro fertilization (IVF).

The EFI system takes into account:

  • Age
  • Duration of infertility
  • Previous pregnancies
  • Function of the ovary, fallopian tubes, and fimbria
  • Extensiveness of endometriosis

Descriptive Classifications

Endometriosis can also be classified using descriptive categories. The Endometriosis Foundation of America classifies the disease based on its location within the pelvic and abdominal cavity:

  • Category 1: Minimal form of endometriosis that involves the peritoneum
  • Category 2: Ovarian endometriomas (chocolate cysts)
  • Category 3: A form of deep-infiltrating endometriosis that involves organs within the pelvic cavity
  • Category 4: A form of deep infiltrating endometriosis that involves organs within and outside of the pelvic cavity

Diagnostic Challenges

While staging endometriosis is comparatively straightforward, diagnosing endometriosis in the first place can be challenging. This is partly because many common symptoms, such as pelvic and abdominal pain, can be caused by other health conditions.

It takes an average of 10 years after the onset of symptoms for an official diagnosis of endometriosis to be made. Around 70% of women with chronic pelvic pain are found to have endometriosis.

Making Sense of Endometriosis Staging

People often think the stages of endometriosis are determined similarly to cancer stages, but endometriosis doesn’t spread or grow the same way cancer does.

Here are some facts about endometriosis stages that can help you better understand what they mean (and don't) in terms of your disease course and prognosis.

Spread and Symptoms

Cancer starts in one part of the body and spreads to distant organs. As cancer progresses, a person usually feels sicker, may have more pain, and has more complications related to the disease.

In contrast, endometriosis can be widespread even in the early stages. The disease stage doesn't necessarily correlate with someone's symptoms, pain level, quality of life, or complications like digestive problems and fertility issues—and researchers do not know why.

Stage Progression

Unlike other diseases that can be staged, endometriosis won't necessarily progress through the stages in a predictable way.

Research has shown that without treatment (particularly if diagnosed during adolescence) endometriosis might improve, get worse, or stay the same.

Meaning for Prognosis and Treatment

Researchers also aren't sure why some people have severe disease and others do not. There is currently no method to predict which outcome a person with endometriosis will have.

These stages also don't offer much guidance in terms of treating endometriosis.

Endometriosis needs to be evaluated on a case-by-case basis, and each patient will need an individualized approach to treating the disease and managing symptoms.


Endometriosis is commonly classified into one of four stages: 1-minimal, 2-mild, 3-moderate, and 4-severe. These endometriosis stages are largely based on the number of endometrial implants and their location and depth.

There are other staging methods that can also be used to characterize other aspects endometriosis. These include the ENZIAN classification system, the endometriosis fertility index (EFI), and other descriptive classifications.

Surgery (to look inside the pelvis and abdomen) is required to confirm a diagnosis of endometriosis and determine the disease stage.

19 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  1. Alimi Y, Iwanga J, Loukas, et al. The clinical anatomy of endometriosis: A review. Cureus. 2018;10(9):e3361. doi:10.7759/cureus.3361

  2. Johnson NP, Hummelshoj L, Adamson GD, et al. World Endometriosis Society consensus on the classification of endometriosisHum Reprod. 2017;32(2):315-324. doi:10.1093/humrep/dew293

  3. Nisenblat V, Bossuyt PM, Farquhar C, Johnson N, Hull ML. Imaging modalities for the non-invasive diagnosis of endometriosis. Cochrane Database Syst Rev. 2016;2(2):CD009591. doi:10.1002/14651858.CD009591.pub2

  4. Rolla E. Endometriosis: advances and controversies in classification, pathogenesis, diagnosis, and treatment. F1000Res. 2019;8:F1000. doi:10.12688/f1000research.14817.1

  5. Subramanian A, Agarwal N. Endometriosis - Morphology, clinical presentations and molecular pathologyJ Lab Physicians. 2010;2(1):1. doi:10.4103/0974-2727.66699

  6. Endometriosis.org. About endometriosis.

  7. Grandi G, Toss, A, Coresti L, et al. The association between endometriomas and ovarian cancer: Preventive effect of inhibiting ovulation and menstruation during reproductive life. Biomed Res Int. 2015;2015:751571. doi:10.1155/2015/751571

  8. Vercellini P, Viganò P, Somigliana E, et al. Endometriosis: pathogenesis and treatment. Nat Rev Endocrinol. 2014;10(5):261-75. doi:10.1038/nrendo.2013.255

  9. Wallwiener M, Brölmann H, Koninckx PR, et al. Adhesions after abdominal, pelvic and intra-uterine surgery and their prevention. Gynecol Surg. 2012;9(4):465-466. doi:10.1007/s10397-012-0762-4

  10. De wilde RL, Alvarez J, Brölmann H, et al. Adhesions and endometriosis: challenges in subfertility management : (An expert opinion of the ANGEL-The ANti-Adhesions in Gynaecology Expert PaneL-group). Arch Gynecol Obstet. 2016;294(2):299-301. doi:10.1007/s00404-016-4049-2

  11. Zondervan KT, Becker CM, Koga K, Missmer SA, Taylor RN, Viganò P. Endometriosis. Nat Rev Dis Primers. 2018;4(1):9. doi:10.1038/s41572-018-0008-5

  12. Ozkan S, Murk W, Arici A. Endometriosis and Infertility. Annals of the New York Academy of Sciences. 2008;1127(1):92-100. doi:10.1196/annals.1434.007

  13. Lee SY, Koo YJ, Lee DH. Classification of endometriosisYeungnam Univ J Med. 2021;38(1):10-18. doi:10.12701/yujm.2020.00444

  14. Endometriosis Foundation of America. Endometriosis stages:Understanding the different stages of endometriosis.

  15. Agarwal SK, Chapron C, Giudice LC, et al. Clinical diagnosis of endometriosis: a call to action. Am J Obstet Gynecol. 2019;220(4):354.e1-354.e12. doi:10.1016/j.ajog.2018.12.039

  16. Parasar P, Ozcan P, Terry, KL. Endometriosis: Epidemiology, diagnosis and clinical managementCurr Obstet Gynecol Rep. 2017;6(1):34-41. doi:10.1007/s13669-017-0187-1

  17. U.S. Department of Health and Human Services National Institutes of Health National Cancer Institute. Cancer staging. National Cancer Institute.

  18. Brosens I, Gordts S, Benagiano G. Endometriosis in adolescents is a hidden, progressive and severe disease that deserves attention, not just compassionHuman Reproduction. 2013;28(8):2026-2031. doi:10.1093/humrep/det243

  19. Koninckx PR, Ussia A, Keckstein J, et al. Evidence-Based Medicine: Pandora's box of medical and surgical treatment of endometriosis. J Minim Invasive Gynecol. 2018;25(3):360-365. doi:10.1016/j.jmig.2017.11.012

Additional Reading

By Lana Barhum
Lana Barhum has been a freelance medical writer since 2009. She shares advice on living well with chronic disease.