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Endometriosis: What Are The 4 Stages And Symptoms?

November 19, 2021

Female health

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Endometriosis is the second most common gynaecological condition in the UK, affecting 1.5 million women, that’s around the same number who are affected by diabetes, but getting a diagnosis can take several years.

Here we look at the 4 stages of endometriosis and the symptoms to look out for.

Because the symptoms can vary from woman to woman and can overlap with other health conditions, endometriosis can be difficult to diagnose. The average length of time to diagnosis is over 7 years. Not only does diagnosis take such a long time, but many women do not seek medical help for their symptoms.

What Is Endometriosis?

Endometriosis is a condition where endometrium cells grow outside of the womb in other areas of the body, particularly in or around the pelvis or abdomen. During the menstrual cycle, the endometrium cells build up and are shed, they leave the body when you have a period.

The same is true for the endometrium-like cells that build up elsewhere, but they eventually have nowhere to go, leading to inflammation, cysts, and scarring which can cause painful symptoms.

What Are The 4 Stages of Endometriosis?

Endometriosis is classified into 4 stages depending on the location within the body and the amount of tissue present.

The most used scale for defining the stages of endometriosis is from the American Society of Reproductive Medicine (ASRM) [1]. The scale considers the location, size, and depth of the implanted endometriosis cells, how severe the adhesions are, and the size of endometriomas, dark, fluid-filled cysts [2, 3].

Stage 1: Minimal

Stage 1 endometriosis is also called minimal. In these cases, there are a few small implants of endometrium-like cells. They are often found on organs or within the pelvis or abdomen [2].

Stage 2: Mild

Stage 2 or mild endometriosis means there are more implants than in stage 1. There may also be some more scar tissue present as the cells embed deeper into the tissue [2].

Stage 3: Moderate

Also known as moderate endometriosis, this stage means there are many deep, visible implants. It’s also likely that there are cysts present on the ovaries as well as thick scar tissue, called adhesions [2].

Stage 4: Severe

Severe endometriosis or stage 4 is the most widespread stage of the condition. Here, it is likely that you’ll have lots of deep implanted cells around the body. You may also have large cysts on one or both of your ovaries [2].

How Serious Is Stage 4 Endometriosis?

Most women who have endometriosis fall within a minimal to mild stage. Although, the stage doesn’t always tell us everything with regards to the severity of the symptoms because some women can have severe pain but be in stage 1.
In terms of severity, stage 3 and 4 are most often characterised by endometriomas on the ovaries, also known as ‘chocolate cysts’ because of their dark brown appearance. These cysts are associated with chronic pelvic pain and infertility [3].

How Do You Know What Stage Of Endometriosis You Have?

To find out what stage of endometriosis you have, you’ll need a diagnosis. Getting diagnosed isn’t easy due to the differing and overlapping symptoms. In the UK, the average time it takes to get a diagnosis is 7.5 years [4].

The only way to get a definite endometriosis diagnosis is by having a laparoscopy, a procedure where a small camera called a laparoscope is inserted into the pelvis through a small incision in the abdomen.

The camera enables a gynaecologist to look for signs of endometriosis in the pelvic organs. If it is discovered, the cells may be removed for further investigation.

Other Classification Methods

As well as the ASRM’s numbered stages classification, there is also a descriptive categorisation of the condition proposed by the Endometriosis Foundation of America (Endofound).

The Endofound method classifies endometriosis according to the location of the condition i.e., whether it’s in the pelvis or abdomen, as follows:

  1. Peritoneal endometriosis – a minimal form of endometriosis found in the

    membrane that lines the abdomen called the peritoneum.
  2.  Ovarian Endometriomas – where endometriosis has already formed in the ovaries

    causing chocolate cysts.
  3.  Deep Infiltrating Endometriosis I – the first form of deep infiltrating endometriosis

    and found with in the pelvis affecting structures including the ovaries, rectum, and

  4. Deep Infiltrating Endometriosis II – as above but affects organs both inside and

    outside the pelvis such as the bowels, diaphragm, heart, lungs, and brain [5].

How Fast Does Endometriosis Progress?

Endometriosis is a chronic-long-term condition and how quickly it can progress is not known.


According to the ASRM, endometriosis can be categorised into 4 stages, ranging from minimal to severe. To find out what stage endometriosis you may have, you will need a laparoscopy.

The symptoms of endometriosis can overlap with other gynaecological conditions and can vary between women, ultimately making diagnosis difficult. However, if you think you may have symptoms you should consult your doctor for further advice.

Read Next: Endometriosis Awareness – Why More Needs to Be Done>>

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This information has been medically reviewed by Dr Nicky Keay

Nicola has extensive clinical and research experience in the fields of endocrinology and sport and exercise medicine. Nicky is a member of the Royal College of Physicians, Honorary Fellow in the Department of Sport and Exercise Sciences at Durham University and former Research Fellow at St. Thomas' Hospital.

Dr Nicky Keay

Dr Nicky Keay

BA, MA (Cantab), MB, BChir, MRCP.