The stages of endometriosis, and why stage 1 can hurt more than stage 4
Stage 1 to stage 4 endometriosis explained: what the rASRM score counts, why it does not predict pain, and what to track when you have no stage at all.
Two women sit in the same waiting room. One has stage 1 endometriosis and has missed nine days of work this year. The other has stage 4 and found out by accident, during surgery for something else, because she had never had much pain.
This is not a rare mix-up. It is what the staging system does, and knowing why saves a lot of grief when your stage arrives and does not match your life.
The short version: the four stages measure how much disease a surgeon can see and how stuck together your pelvis is. They were built to estimate fertility, not pain. They do not predict how much you hurt, they cannot be assigned without surgery, and most people with endometriosis will never have one.
What the four stages actually are
The system in use is the revised American Society for Reproductive Medicine classification, usually written rASRM, in its 1996 form. A surgeon looks inside the pelvis during laparoscopy and awards points for what is there.
Points go to the size of lesions on the peritoneum and on the ovaries, to whether those lesions are superficial or deep, to adhesions binding the ovaries and tubes and whether they are filmy or dense, and to obliteration of the cul-de-sac, the pouch behind the uterus.
| Stage | Name | Points |
|---|---|---|
| 1 | Minimal | 1 to 5 |
| 2 | Mild | 6 to 15 |
| 3 | Moderate | 16 to 40 |
| 4 | Severe | more than 40 |
Read the point list again and notice what is not in it. There is no line for how much it hurts. There is no line for how many days you lost, whether sex is painful, whether you dread opening your bowels during your period, or whether the fatigue is the part that has actually taken your life apart. None of that is scored, because none of it can be seen through a camera.
Why the stage does not predict the pain
Three things in the anatomy explain most of the mismatch.
Depth matters more than area. A large patch of superficial disease spread over the peritoneum scores few points. A small deeply infiltrating nodule, particularly one sitting against the uterosacral ligaments or the bowel, scores modestly but sits where the nerves are. Depth of infiltration tracks pain considerably better than total surface area, and the score barely distinguishes the two.
Endometriomas inflate the number. A cyst on the ovary is easy to see, easy to measure and worth a lot of points, so it pushes people into stage 3 and stage 4. Endometriomas are a genuine problem for fertility and for surgery. They are not, by themselves, a reliable source of daily pain.
Long-standing pain stops depending on the lesion. Pain that has run for years changes how the nervous system processes signals from the pelvis, so the pain becomes partly self-sustaining rather than purely a readout of tissue damage. This is the best explanation for the case that frustrates everyone, where a surgeon removes everything visible and the pain comes back or never left. It also explains pain that started out strictly cyclical and has since spread across the whole month.
So a number built on visible tissue was never going to track a symptom that depends on depth, nerve proximity and time. It does not, and that is a property of the tool, not a sign that you are exaggerating or coping badly.
What the staging system was built for
Fertility, mostly. The classification grew out of an attempt to predict who would conceive after surgery and to give surgeons a shared vocabulary for describing cases in papers. Judged as a communication tool it does a reasonable job. Judged as a fertility predictor it is mediocre, which is why other systems exist.
The Endometriosis Fertility Index, published by Adamson and Pasta in 2010, predicts natural conception considerably better because it looks at more than the disease. It combines the surgical findings with the function of the tubes and ovaries at the end of the operation, your age, how long you have been trying, and whether you have been pregnant before. Those are the things that actually move the odds.
For deep disease, the Enzian classification describes where the disease sits by compartment and how deep it goes, which is what a surgeon planning a difficult operation needs to know. The 2021 AAGL system sorts cases by surgical complexity instead, essentially answering how hard this operation will be and who should perform it.
None of these is a pain scale either. That gap is not an oversight; nobody has yet produced an anatomical score that predicts symptoms well, and there is a reasonable argument that no such score can exist.
You may never have a stage, and that is now normal
Until recently a diagnosis meant surgery, which meant everyone who was diagnosed got a stage. The 2022 ESHRE guideline changed that: laparoscopy is no longer the required gold standard. Endometriosis can now be diagnosed on symptoms together with ultrasound or MRI findings, and treatment for pain can start without an operation.
That is good news for the eight years of delay that a UK parliamentary inquiry documented in 2020, a figure that had not improved in the decade before it. It comes with one consequence worth being blunt about.
A normal scan does not rule endometriosis out. Ultrasound and MRI see endometriomas and deep nodules fairly well. Superficial peritoneal disease, the most common form, is largely invisible to both. A clear scan means no cyst and no deep nodule was found. It does not mean there is nothing there, and it is not a reason to stop investigating symptoms that fit.
What to bring instead of a stage
Since the number is not available to most people and does not describe symptoms anyway, the useful question is what does. In a ten minute appointment the things that change decisions are these.
- Which days hurt, and how much. Not an average. Averages hide the days that ruin a week.
- Where it sits. Pelvis, lower back, one side, radiating down a leg, deep during sex, on opening your bowels, on passing urine.
- How it lines up with your cycle. This is the single most informative pattern, and it is the one a single appointment cannot see. Pain that clusters around bleeding, or in the few days before, points somewhere specific. So does pain that used to cluster and no longer does.
- What you took and whether it worked. Drug, dose, timing, and the honest answer about effect. This is what tells a doctor whether the current plan has actually been tried.
- What it cost you. Hours or days lost from work, study, childcare or sleep. Impact is what moves referrals.
Recall over six months is not reliable enough for any of that, which is the entire argument for writing it down as it happens. How to keep an endometriosis pain diary covers exactly what to record and, just as importantly, what to leave out so the habit survives past week two.
EndoPainOS is the version of that record we build: daily pain with a body map, cycle day attached automatically so the pattern shows itself, painkiller log, and a summary you can hand over. EndoReliefOS is the wider one, covering surgery preparation, appointments and a food and symptom log alongside the pain record. Both run offline in your browser and keep the data on your own device, which matters here more than in most subjects. A paper notebook does the same job, more slowly. So does a general symptom journal if endometriosis is one of several things you are managing.
If the cycle itself is the part that is unclear, how long a normal menstrual cycle is and the phases of the cycle are the background, and the period calculator will give you the cycle days to write against.
When a stage does matter
Having spent this long saying the number is oversold, there are two situations where it is worth knowing.
Planning fertility treatment. Stage, and more usefully the Endometriosis Fertility Index, does inform the conversation about whether to try naturally, for how long, and when to move to IVF. This is the job the system was designed for.
Planning surgery. Stage 4 with an obliterated cul-de-sac is a different operation from a few superficial spots, and knowing that in advance decides how long to book, which specialist should operate and whether a bowel surgeon should be in the room. A stage assigned at a previous operation genuinely helps the next one.
Outside those two, the number tells you less about your own body than a month of honest notes will. If you have a stage that does not match your experience, you are not the outlier. You are the normal case, and the scale is the thing that does not fit.
Frequently asked questions
What are the four stages of endometriosis?
Stage 1 is minimal, stage 2 mild, stage 3 moderate and stage 4 severe, under the revised American Society for Reproductive Medicine system. A surgeon assigns points during laparoscopy for the size and depth of lesions, whether an ovary is involved, and how much scar tissue is present. One to five points is stage 1, six to fifteen is stage 2, sixteen to forty is stage 3, and more than forty is stage 4.
Does stage 4 endometriosis hurt more than stage 1?
Not reliably. The staging score counts how much tissue a surgeon can see and how stuck together the pelvis is, and neither of those tracks pain closely. Stage 1 disease can be disabling, and stage 4 is sometimes found by accident during surgery for something else in a woman who had no pain at all. If your stage does not match how you feel, the stage is the thing that is wrong.
What was the endometriosis staging system designed for?
Fertility, not pain. It was built to estimate the chance of conceiving after surgery and to let surgeons describe cases to each other in the same language. It was never designed as a measure of symptoms, which is why using it that way produces such odd results.
Can you be diagnosed with endometriosis without surgery?
Yes. The 2022 ESHRE guideline dropped laparoscopy as the required gold standard. A diagnosis can now rest on symptoms plus ultrasound or MRI findings, and treatment for pain can begin without surgical confirmation. An important consequence is that a normal scan does not rule endometriosis out, because superficial disease is usually invisible on imaging.
Why does endometriosis take so long to diagnose?
Reported delays commonly run between seven and ten years. A UK parliamentary inquiry in 2020 put the average at eight years and found it had not improved in a decade. The usual causes are period pain being treated as normal, symptoms that look like irritable bowel or bladder problems, and the fact that the most common form of the disease does not show up on a scan.
Does removing endometriosis lesions end the pain?
Often it helps, and sometimes it does not, even when the surgeon removes everything visible. Pain that has been present for years can become partly self-sustaining in the nervous system, which is why pain can persist after clear surgery and why treatment usually combines more than one approach rather than relying on surgery alone.
What should I track if I do not have a stage?
Track what actually changes decisions: which days hurt and how much, where the pain sits, how it lines up with your cycle, what medication you took and whether it worked, and what you could not do because of it. That record is more useful in a ten minute appointment than a stage number, and most people with endometriosis will never have a stage at all.
Medical disclaimer: This guide is for general information and education only. It is not medical advice, diagnosis or treatment, and it is not written by a clinician. A planner is a place to keep your own notes, including notes you may want to show your doctor. Always talk to your doctor or midwife about your health and any decisions.
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