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Medical Professionals

Professional Reference articles are designed for health professionals to use. They are written by UK doctors and based on research evidence, UK and European Guidelines. You may find the Endometriosis article more useful, or one of our other health articles.

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What is endometriosis?

Endometriosis is a chronic, oestrogen-dependent condition characterised by the growth of endometrial tissue in sites other than the uterine cavity, most commonly the pelvic cavity (including the ovaries), the uterosacral ligaments, the pouch of Douglas, the rectosigmoid colon, and the bladder and distal ureter.

Other sites are rarely involved but include the umbilicus, scar sites (eg, following caesarean section and laparoscopy), the pleura and pericardium, and the central nervous system.

Adenomyosis is the invasion of the myometrium by endometrial tissue. Extrauterine endometrial tissue causes inflammation, pain and the formation of adhesions. Clinically its significance is as a cause of chronic pelvic pain, dyspareunia and female infertility.1

How common is endometriosis? (Epidemiology) 1

  • Endometriosis is one of the most common gynaecological disorders in women of reproductive age. Endometriosis is the second most common gynaecological condition (after fibroids).

  • The prevalence is not known accurately because of variability in clinical presentation. Some women with endometriosis may be asymptomatic.

  • The only reliable diagnostic test is laparoscopy. It takes an average of 7.5 years from the onset of symptoms before endometriosis is diagnosed.

  • Endometriosis affects approximately 10% of women of reproductive age in the UK.

  • The prevalence of endometriosis in women with infertility is about 30-50%.

Risk factors

  • Risk factors include: an early menarche, late menopause, delayed childbearing and nulliparity.

  • Obstruction to vaginal outflow - eg, hydrocolpos, female genital mutilation or defects in the uterus or Fallopian tubes.

  • Genetic factors:

    • Risk for first-degree relatives of women with severe endometriosis is six times higher than that for relatives of unaffected women.

    • Familial aggregation has been shown in clinical and population-based samples and in twin studies.2

  • Other risk factors include white ethnicity, low body mass index (BMI) and smoking.

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Causes of endometriosis (aetiology)1

The exact cause of endometriosis is unknown. It is thought that endometriosis may develop as a result of a combination of the following possible theories/factors:

  • Retrograde menstruation: endometrial cells flow backwards from the uterine cavity, through the Fallopian tubes, and implant on pelvic organs.

  • Lymphatic or circulatory dissemination: it has been suggested that endometriotic tissue may also be able to travel to distant sites (such as the lungs, eyes, and brain) through the lymphatic system or in the bloodstream.

  • Genetic predisposition.

  • Metaplasia: cells in the pelvic and abdominal area change into endometrial-type cells. of the germinal epithelium.

  • Environmental factors: this theory suggests that certain environmental toxins can affect the body, immune system, and reproductive system and cause endometriosis.

  • Immune dysfunction: many women with endometriosis appear to have reduced immunity to other conditions.

Symptoms of endometriosis (presentation)

Common symptoms include:

Other symptoms may include bloating, lethargy, constipation and low back pain. Less common symptoms include cyclical rectal bleeding, menorrhagia, diarrhoea and haematuria.

The clinical presentation is variable, with some women experiencing several severe symptoms and others having no symptoms at all. The severity of symptoms tends to increase with age.

  • Women with endometriosis may have no symptoms and be diagnosed incidentally or during investigations for infertility.

  • The appearance or worsening of symptoms at the time of menstruation, or just prior to it, suggests endometriosis.

  • Other symptoms include lower urinary tract symptoms (eg, dysuria), painful defecation, abdominal pain, backache, menstrual irregularity, and cyclical pain or bleeding (eg, epistaxis, haemoptysis) at extrapelvic sites.


  • Examination is often normal.

  • However, there may be:

    • Posterior fornix or adnexal tenderness.

    • Palpable nodules in the posterior fornix or adnexal masses (endometriosis can cause cystic lesions on the ovaries, known as 'chocolate cysts').

    • Bluish haemorrhagic nodules visible in the posterior fornix.

    The National Institute for Health and Care Excellence (NICE) recommends abdominal and pelvic examination for women with suspected endometriosis to identify abdominal masses and pelvic signs, such as reduced organ mobility and enlargement, tender nodularity in the posterior vaginal fornix, and visible vaginal endometriotic lesions. If a pelvic examination is not appropriate, offer an abdominal examination to exclude abdominal masses.3

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Differential diagnosis

Diagnosing endometriosis (investigations)

  • For a definitive diagnosis of most forms of endometriosis, laparoscopy is the gold standard investigation but it is invasive with a small risk of major complications - eg, bowel perforation.2

  • There are two possible approaches - refer for a definitive diagnosis, or treat empirically in primary care. Both are of equal value and should be discussed with the patient, although options in primary care are limited for a woman who is trying to conceive and so referral is more likely to be appropriate in this situation.

  • Symptoms and laparoscopic appearance do not always correlate.

  • Transvaginal ultrasound scanning appears to be a useful test, both to make and to exclude the diagnosis of an ovarian endometrioma. A negative scan doesn't exclude the diagnosis - this must be explained to the patient at the time of requesting the scan. 2

  • MRI scan may be a useful non-invasive tool in diagnosis, especially for subperitoneal deposits, but it is only appropriate in secondary care.

  • CA 125 measurement is not recommended for diagnosing or ruling out endometriosis.2

In an acute setting, blood tests (eg, FBC), urinalysis and MC&S, cervical swabs (MC&S, chlamydia testing) and beta human chorionic gonadotrophin (beta-hCG) may be helpful in excluding some important differentials.

The NICE guidelines for the management of endometriosis advise on recognition of symptoms and diagnosis, as well as treatments for symptom control and when a couple are trying to conceive:3

  • Transvaginal ultrasound can be used to investigate suspected endometriosis even if the pelvic and/or abdominal examination is normal and also to identify endometriomas and deep endometriosis involving the bowel, bladder or ureter.

  • Pelvic MRI should not be used as the primary investigation to diagnose endometriosis in women with symptoms or signs suggestive of endometriosis. However, it might be used in secondary care to assess the extent of deep endometriosis involving the bowel, bladder or ureter.

  • When pelvic MRI scans are used in assessment of pelvic pain symptoms, they should be interpreted by a healthcare professional with specialist expertise in gynaecological imaging.

Management of endometriosis 4

  • The treatment of endometriosis is usually individually based, depending on the nature and severity of symptoms and the need for future fertility.

  • Medical treatment may reduce symptoms in 80-90% of patients but none of the treatment options has been shown to reduce recurrence of symptoms once treatment has stopped.2

  • Suppression of ovarian function for at least six months is the basis for most medical treatment, and the options include the combined oral contraceptive (COC) pill, medroxyprogesterone acetate and gonadotrophin-releasing hormone (GnRH) agonist.

  • The levonorgestrel intrauterine device has been shown to be effective even after three years of use.

  • Surgical options include removing severe and deeply infiltrating lesions (which may reduce pain related to endometriosis), ovarian cystectomy (for endometriomas), adhesiolysis and bilateral oophorectomy (often with a hysterectomy).

  • The multidisciplinary team for endometriosis management may also include pain management specialists and clinical psychologists.


For pain, the general principle is to create a pseudo-pregnancy or pseudo-menopause, whilst the treatment of infertility requires a different approach.

  • For laparoscopically confirmed disease, suppression of ovarian function for six months reduces endometriosis-associated pain.

  • Effective hormonal drugs include the COC pill, danazol, oral or depot medroxyprogesterone acetate, the levonorgestrel intrauterine system and GnRH analogues. Approximately 80-85% of patients improve with treatment.

  • Ablation of endometrioid lesions reduces endometriosis-associated pain.

Drugs 21

  • Non-steroidal anti-inflammatory drugs (eg, naproxen) may be effective in reducing the pain associated with endometriosis, although the evidence to date is inconclusive.5

  • Paracetamol, with or without added codeine, is an alternative.

All of the following options must be started in secondary care:

  • Danazol is effective in treating endometriosis but its use is limited by androgenic side-effects.6

  • GnRH analogues (GnRH agonists) appear to be effective at relieving pain associated with endometriosis.7

  • GnRH agonist therapy given for three months may be as effective as treatment given for six months in relieving endometriosis-associated pain. If longer or repeated treatment is required, GnRH agonist use can be extended with 'add-back' therapy (a low-dose oestrogen, progestogen or tibolone to relieve menopausal side-effects and prevent bone loss). 2


NICE recommends to consider referring women to a gynaecology service for an ultrasound scan or gynaecology opinion if3 :

  • They have severe, persistent or recurrent symptoms of endometriosis.

  • They have pelvic signs of endometriosis.

  • Initial management is not effective, is not tolerated or is contra-indicated.


  • Laparoscopic excision at the time of diagnostic laparoscopy. Excision should be considered in preference to ablation.1

  • Hysterectomy with salpingo-oophorectomy is reserved for women as a last resort.

  • It is uncertain as to whether laparoscopic surgery reduces overall pain associated with endometriosis. 8


  • Medical treatment for endometriosis should be avoided for women who are trying to conceive.2

  • In minimal-mild endometriosis, suppression of ovarian function to improve fertility is not effective but ablation of endometrioid lesions plus adhesiolysis is effective compared to diagnostic laparoscopy alone.9

  • The use of laparoscopic surgery in the treatment of subfertility related to minimal and mild endometriosis may improve future fertility. 8

  • In vitro fertilisation (IVF) is appropriate treatment, especially if there are co-existing causes of infertility and/or other treatments have failed.10

Complications of endometriosis

  • A review found an association between endometriosis and some histological subtypes of ovarian cancer, but the magnitude of the absolute risk increase is not clear.

  • Infertility: moderate-to-severe endometriosis can cause tubal damage leading to infertility. Lesser degrees of endometriosis, even in the absence of any obvious tubal damage, are also associated with subfertility and increased risk of ectopic pregnancy.

  • Adhesion formation may occur due to the endometriosis or following surgery.

  • Women with endometriosis have an increased risk of inflammatory bowel disease. 9


  • The prognosis is variable. It is unclear whether endometriosis is always progressive, remains stable, or improves with time.

  • Endometriosis can be a chronic disease affecting women throughout their reproductive lives, and sometimes beyond the menopause.

  • For the majority of women, symptoms can be controlled with hormonal treatment. Some women have complex needs and require long-term support.

  • Studies in untreated women with infertility suggest that endometriotic deposits can spontaneously regress in up to 30% of women, and progress is around 50% over 6-12 months.

  • Recurrence after surgery ranges from 10-50% at one year and increases over time.

    Dr Hazell has written and reviewed educational material on endometriosis for a variety of organisations, including but not limited WebMD, Cogora, RCGP and PCWH.

Further reading and references

  • Endometriosis UK
  1. Endometriosis; NICE CKS, October 2023 (UK access only)
  2. Becker CM, Bokor A, Heikinheimo O, et al; ESHRE guideline: endometriosis. Hum Reprod Open. 2022 Feb 26;2022(2):hoac009. doi: 10.1093/hropen/hoac009. eCollection 2022.
  3. Endometriosis: diagnosis and management; NICE Guidelines (Sept 2017 - last updated April 2024)
  4. Engemise S, Gordon C, Konje JC; Endometriosis. BMJ. 2010 Jun 23;340:c2168. doi: 10.1136/bmj.c2168.
  5. Brown J, Crawford T, Allen C, et al; Nonsteroidal anti-inflammatory drugs for pain in women with endometriosis. Cochrane Database Syst Rev. 2017 Jan 23;1(1):CD004753.
  6. Ferrero S, Remorgida V, Venturini PL; Endometriosis. Clin Evid (Online). 2010 Aug 13;2010. pii: 0802.
  7. Brown J, Pan A, Hart RJ; Gonadotrophin-releasing hormone analogues for pain associated with endometriosis. Cochrane Database Syst Rev. 2010 Dec 8;(12):CD008475. doi: 10.1002/14651858.CD008475.pub2.
  8. Bafort C, Beebeejaun Y, Tomassetti C, et al; Laparoscopic surgery for endometriosis. Cochrane Database Syst Rev. 2020 Oct 23;10(10):CD011031. doi: 10.1002/14651858.CD011031.pub3.
  9. Chiaffarino F, Cipriani S, Ricci E, et al; Endometriosis and inflammatory bowel disease: A systematic review of the literature. Eur J Obstet Gynecol Reprod Biol. 2020 Sep;252:246-251. doi: 10.1016/j.ejogrb.2020.06.051. Epub 2020 Jun 26.
  10. Surrey ES; Endometriosis-Related Infertility: The Role of the Assisted Reproductive Technologies. Biomed Res Int. 2015;2015:482959. doi: 10.1155/2015/482959. Epub 2015 Jul 9.
  11. Kralickova M, Lagana AS, Ghezzi F, et al; Endometriosis and risk of ovarian cancer: what do we know? Arch Gynecol Obstet. 2020 Jan;301(1):1-10. doi: 10.1007/s00404-019-05358-8. Epub 2019 Nov 19.

Article history

The information on this page is written and peer reviewed by qualified clinicians.

  • Next review due: 22 Jun 2027
  • 23 Jun 2024 | Latest version

    Last updated by

    Dr Toni Hazell

    Peer reviewed by

    Dr Pippa Vincent, MRCGP
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