What Is Endometriosis? Symptoms, Diagnosis and Treatment

What is endometriosis?

Endometriosis is a condition where tissue similar to the lining of the womb grows in other parts of the body, most often around the womb, on the ovaries and fallopian tubes, and on the lining of the pelvis. The NHS says it can also affect the bladder and bowel, and sometimes areas outside the pelvis such as the chest. It affects around 10% of women of reproductive age, roughly 190 million worldwide, on World Health Organization figures cited by NICE Clinical Knowledge Summaries (CKS).

The tissue responds to oestrogen. The American College of Obstetricians and Gynecologists (ACOG) explains that it can grow and bleed like the womb lining, causing inflammation and scar tissue (adhesions) that can make organs stick together. Patches can sit on the surface of organs or grow into the bladder or bowel wall, and on the ovaries they can form cysts called endometriomas.

What are the symptoms of endometriosis?

NICE guideline NG73 tells clinicians to suspect endometriosis, including in young women aged 17 and under, if you have one or more of:

• long-term pelvic pain
• period pain that affects daily activities and quality of life
• deep pain during or after sex
• bowel symptoms linked to periods, especially painful bowel movements
• urinary symptoms linked to periods, especially blood in the urine or pain passing urine
• difficulty getting pregnant alongside any of the above

The NHS adds heavy periods, extreme tiredness, and low mood or anxiety. ACOG notes that pain does not always match how much endometriosis there is: slight pain can come with many lesions, and severe pain with very few. Some people have no symptoms and find out only when investigated for fertility problems. NICE suggests keeping a pain and symptom diary.

What causes endometriosis?

The cause is unknown; NICE CKS lists several theories, none of which explains every case. The best known is retrograde menstruation, where period blood flows backwards through the fallopian tubes, but up to 90% of women have some retrograde flow and most never develop endometriosis.

Genes play a part. NICE CKS reports that having a first-degree relative (a mother, sister or daughter) with endometriosis raises your risk 7 to 10 times and that heritability may be up to 50%, but no specific gene has been identified and there is no genetic test. NICE now asks clinicians to check family history.

How is endometriosis diagnosed?

In the UK, since NICE's 2024 update, if endometriosis is suspected your GP practice should arrange a transvaginal ultrasound scan, even if an examination is normal, and investigations and referral should run alongside initial treatment rather than after it. A normal scan does not rule endometriosis out.

A laparoscopy is keyhole surgery, usually under general anaesthetic, and endometriosis may be removed during it. ACOG says it is the only way to confirm the diagnosis, but it is no longer a gatekeeper to treatment. ESHRE's 2022 guideline challenges laparoscopy as the "gold standard", recommends ultrasound or MRI, and found no evidence that diagnostic surgery controls symptoms better than imaging plus hormonal treatment. In the US, ACOG calls transvaginal ultrasound the best test, says you can start treatment before imaging, and says you are not required to have surgery to be treated.

What are the stages of endometriosis?

Surgeons often record endometriosis as stage I to IV under the revised American Society for Reproductive Medicine (rASRM) system, and ESHRE's fertility recommendations are framed around these stages. Stage does not reliably match pain, and NICE recommends basing treatment on your symptoms, preferences and priorities rather than the stage.

How is endometriosis treated?

There is no cure, the NHS says, but treatment can manage symptoms. NICE NG73 sets out the options:

• Painkillers. A short trial, for example 3 months, of paracetamol or an anti-inflammatory (NSAID), alone or together, then other options and referral if needed.
• Hormonal treatment, such as the combined pill or a progestogen. NICE says it can reduce pain and has no permanent negative effect on later fertility. ACOG adds that it does not remove existing endometriosis, and pain often returns when it stops.
• Newer hormone medicines. NICE recommends two GnRH antagonist treatments, linzagolix with add-back therapy and relugolix–estradiol–norethisterone, as options for adults of reproductive age after medical or surgical treatment.
• Specialist care. Endometriomas and deep endometriosis should be referred to a specialist endometriosis centre, with access to a colorectal surgeon, a urologist, a specialist nurse and a pain management team.

NICE says the evidence does not support Chinese herbal medicines or supplements for endometriosis.

What does endometriosis surgery involve?

Surgery is usually laparoscopic. Endometriosis is cut out (excision) or destroyed (ablation), and NICE suggests considering excision rather than ablation for endometriomas, taking into account your wish for fertility and your ovarian reserve. It also suggests hormonal treatment afterwards to prolong the benefit. Surgery usually relieves pain, but endometriosis can return: ACOG reports that up to 8 in 10 women have pain again within 2 years. For severe pain that has not responded to other treatment, hysterectomy may be an option, and NICE says all visible endometriosis should be removed at the same time.

Endometriosis and fertility

NICE CKS reports endometriosis in 25% to 40% of infertile women, compared with 0.5% to 5% of fertile women, although the mechanisms are poorly understood and causation is not established. Severe disease can cause adhesions around the fallopian tubes. If fertility is a priority, NICE says removing or destroying endometriosis that does not involve the bowel, bladder or ureter, and freeing adhesions, improves the chance of natural pregnancy, while hormonal treatment does not and should not be offered while you are trying. Trying to conceive with endometriosis sets out the full guidance, and when to see a doctor about fertility covers referral.

Is endometriosis the same as adenomyosis?

No, although symptoms overlap and the two can occur together. In adenomyosis, the NHS explains, the womb lining grows into the muscle of the womb wall; in endometriosis, similar tissue grows outside the womb. Adenomyosis is more commonly diagnosed over 30 and can cause painful, heavy periods, pelvic pain, bloating and pain during sex.

When to seek help

The NHS advises asking for an urgent GP appointment or contacting NHS 111 if your pelvic pain or period pain is severe or worse than usual and painkillers have not helped. See a GP, or in the US a gynaecologist (ob-gyn), if:

• you think you might have endometriosis
• your symptoms are affecting your everyday life, work or relationships
• you have had treatment from a GP but your symptoms have not improved, or have got worse

Frequently asked questions

Is endometriosis cancer?

No. Endometriosis is a long-term condition, not a cancer. NICE CKS says studies suggest an almost two-fold increased risk of ovarian cancer, but that this represents a very small lifetime risk and the evidence has limitations. Associations with thyroid and breast cancer have also been reported, with a low absolute risk.

Does endometriosis go away after menopause?

Usually it improves. ACOG explains that after menopause the ovaries stop making oestrogen, so endometriosis generally stops growing and lesions usually shrink. The NHS says symptoms usually stop after menopause, but that it is possible to have symptoms afterwards, so new or continuing pain is still worth reporting.

Can men get endometriosis?

Very rarely. NICE CKS notes that endometriosis has occurred in some men following exposure to oestrogen through drug treatments, one of the reasons the retrograde menstruation theory cannot explain every case. Otherwise, the NHS describes it as a condition that can affect anyone who has or had a womb.