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Endometriosis affects an estimated 176 million women around the globe, causing many to suffer a life of pain and debilitation and sometimes infertility. It mostly affects women of childbearing age and usually disappears after menopause. Endometriosis is often a long-term condition, with no simple cure. But there are treatments which can help.

Diagram of female feproductive system showing uterus, vagina, ovaries and endometrium.

Endometriosis is a common condition, mostly affecting women during their reproductive life span. Although exact numbers do not exist studies suggest a prevalence of approximately 10%. It is defined by the presence of tissue that closely resembles characteristics of endometrium if it is present outside the uterine cavity.

Endometriosis is a medical condition where cells like those lining the uterus (womb) are found in other parts of the body. Every month these cells react like the womb lining, building up and then breaking away. This inflames the surrounding tissues, causing pain which is often worse just before and during a period.


Women with endometriosis can suffer from symptoms such as:

  • Painful periods
  • Heavy menstrual bleeding
  • Spotting between periods
  • Cyclical and non-cyclical abdominal pain
  • Pain during sexual intercourse
  • Pain when emptying the bladder or their bowels
  • Lower back pain
  • Pelvic pain
  • Fatigue
  • Infertility
  • Feeling bloated

Much less common are symptoms such as:

  • Repeated spontaneous pneumothoraxes (rupture of the lung cavities)
  • Bleeding from Caesarean section scars, the umbilicus, the bowel, bladder or other body openings
  • Bulging and sometimes painful ‘lumps’

Your GP or specialist may examine you depending on your symptoms. This often includes an internal vaginal examination if you agree and it is appropriate. This may identify rare lesions that can be seen in the vagina and also helps the clinician to assess the location and extent of possible disease. Again, depending on your symptoms, your clinical history and the findings during your visit it may be necessary to perform an ultrasound scan or, less likely, an MRI (magnetic resonance imaging) of your pelvis. As the lesions are very often quite small it is not uncommon that the imaging does not show any signs of endometriosis although you may still have it.


Although many theories exist it remains unclear how and when endometriosis develops.

The ‘retrograde menstruation’ theory is the most accepted theory where endometrial tissue and cells enter the abdominal cavity through the Fallopian tubes at the time of the menstrual period.

Studies have demonstrated that endometriosis is also caused by over/under expression of biochemical factors, genetic factors, and/or external factors. These factors cause rapidly spreading of endometrial tissue, attached to the abdominal wall, and invasion into the deeper layers by forming blood vessels for growth.  Increasing evidence suggests that an impaired immune system and inflammation also plays a central role in these processes.

Endometriosis most commonly grow in the following areas, with different appearances, shapes and colours:

  • Ovaries
  • Fallopian Tubes
  • Uterus
  • Ureters
  • Bowels or Bladder
  • Abdominal Wall

However, none of the existing hypotheses have been completely proven and many mechanisms still remain unclear. It is possible that different mechanisms account for different presentations of endometriosis.

The revised American Fertility Society and American Society of Reproductive Medicine staging system of endometriosis is based on a points system that takes into account location, extent and depth of disease in relation to pelvic structures.The revised American Fertility Society and American Society of Reproductive Medicine staging system of endometriosis is based on a points system that takes into account location, extent and depth of disease in relation to pelvic structures.

Organs such as the uterus, fallopian tubes and ovaries as well as structures that include the ovarian fossae (the shallow depression on the lateral wall of the pelvis in which the ovary lies), uterosacral ligaments, rectovaginal septum, pouch of Douglas (the portion of the peritoneal cavity between the rectum and the posterior wall of the uterus and the uterosacral ligaments) and uterovesical fold (the shallow depression of the peritoneum between the uterus and bladder) are often affected. Lesion size can range from punctate spots millimetres in size to nodular structures of a few centimetres and ovarian cysts (endometrioma) the size of grapefruits. Stage I (minimal, 1–5 points) usually comprises few superficial endometriotic spots or adhesions. Stage II (mild, 6–15 points) can be a few, deep peritoneal lesions solely or in combination with superficial lesions and filmy adhesions. Stage III (moderate, 16–40 points) often includes an endometrioma by itself or in combination with superficial or deep endometriosis and/or dense adhesions. Stage IV (severe, >40 points) is often characterised by all of the above as well as bilateral ovarian endometrioma and/or dense adhesions that can lead to a partial or complete obliteration of the lesser or true pelvis (the structure that contains all the pelvic organs). Importantly, the severity of the disease according to this system does not correlate with the severity and location of symptoms. 


This is another area that is still entirely unclear. Endometriosis is almost exclusively found in women who produce sufficient levels of the hormone oestrogen. Some young girls have painful periods, but it is unclear whether these are endometriosis related. Theories exist that connect the onset of endometriosis as far back as to the embryonic or perinatal period. It is unclear why endometriosis suddenly develops, over what time frame, and whether and in whom it gets worse, stays the same or potentially even gets better spontaneously.

Who gets Endometriosis?

The most common risk factors for endometriosis are:

  • Getting your period at an early age
  • Short menstrual cycles
  • Increased menstrual flow
  • Low body mass index
  • Family History
  • Late menopause


The gold standard to detect endometriosis, if it is located in the abdomen, is a laparoscopy (key hole surgery). However, a laparoscopy during which endometriosis could also be treated is an invasive procedure requiring general anaesthesia.

Transvaginal ultrasonography with Doppler flow image of a left-sided endometrioma (panel a) with a typical unilocular ground-glass appearance and minimal vascularity. T1-weighted MRI scan of a female pelvis with bilateral endometrioma (arrows) behind the uterus (asterisk; panel b). Because of their close proximity, this constellation is often called ‘kissing ovaries’. MRI of the pelvis of another female patient with endometriosis (panel c).Transvaginal ultrasonography with Doppler flow image of a left-sided endometrioma (panel a) with a typical unilocular ground-glass appearance and minimal vascularity. T1-weighted MRI scan of a female pelvis with bilateral endometrioma (arrows) behind the uterus (asterisk; panel b). Because of their close proximity, this constellation is often called ‘kissing ovaries’. MRI of the pelvis of another female patient with endometriosis (panel c).

What are the symptoms of endometriosis?

The vast majority of endometriotic lesions are found in the female pelvis. These can have very different appearances, shapes and colours. They can be very superficial or deeply invading the abdominal lining (peritoneum) and organs such as the bowel, the bladder and the ureters (which are two long, tubes located in the posterior pelvic side wall that transport urine from the kidneys to the bladder). The lesions can be red, blue, brown, white, vascular, and look like adhesions, small vesicles, spots of different sizes or very hard nodules. There is some evidence that red lesions are more ‘active’, but it remains unclear what clinical impact this might have.

Is Endometriosis a genetic disease?

Twin studies have shown increased concordance for endometriosis in monozygotic (identical) twins compared to dizygotic (fraternal) twins with heritability estimated at 52%. Although endometriosis often clusters in families, it is not a single-gene (monogenic) disease that is caused solely by inheriting a rare genetic variant from parents. Instead, endometriosis is a common complex condition that is caused by a combination of multiple genetic and environmental factors. Some other examples of common complex conditions include asthma, hypertension and migraine.

We are conducting many studies to identify these multiple genetic variants with small effects that contribute to endometriosis susceptibility. Most common type of genetic variation in our genome is called single nucleotide polymorphisms (SNPs) that are single letter changes in our DNA. We conduct genome-wide association studies (GWAS) that screen endometriosis cases as well as endometriosis free-individuals and compare whether individuals with endometriosis have SNPs that occur more or less commonly compared to endometriosis free-individuals. Identification of the SNPs that are associated with endometriosis enables us to understand the underlying genetic mechanisms that make some women more susceptible to this enigmatic condition.


If you are suffering from endometriosis-associated symptoms, then you probably should be treated.

Treatment approaches ought to be tailored to your specific situation and take into consideration whether you are currently trying to become pregnant or not. Endometriosis is a disease driven by oestrogen, the central female hormone. As such, most medical therapies are hormone based. However, in most circumstances, hormones should not be given if you are trying for a baby. Medical therapy also encompasses specific pain medication and can often be a combination of drugs.

The alternative is surgical therapy, which almost always should mean laparoscopic (key hole) surgery and not open surgery (laparotomy). If you are having surgery, ideally your endometriosis should be treated at the same time. This can be done by removing, burning or evaporation the lesions. It is important to point out that endometriosis treatment, especially surgery, should be performed in a centre with vast experience in the field.

However, surgery is an invasive procedure and not entirely free of risks. Therefore, your doctor rightly may decide with you to assume that you may have endometriosis and treat it medically without surgical proof. This is known as empirical treatment and also frequently done. If your symptoms stop or at least become much better, it may indicate that endometriosis is present, and you are correctly treated. If you do not get better, it does not rule out endometriosis, though, and your doctor might change the medication, discuss the surgical approach or refer you to a specialist in a different field. Read more...


Endometriosis can be associated with subfertility but is usually not an absolute reason. If you have been diagnosed with endometriosis recently or in the past and you are now trying to become pregnant there is a good chance that you are going to be successful. However, if there is a delay, then you might want to consult a fertility and/or endometriosis specialist who will assess you and your partner’s situation and give you some advice. This may include investigations such as blood tests, semen analysis and investigations to check if you Fallopian tubes are open. It may also be suggested to you to have fertility treatment the type of which will depend on many factors. Read more...


Our research studies all focus around improving our understanding of endometriosis, working towards a non-surgical method of diagnosis and identifying new, better treatments. We have a number of research studies running that are recruiting patients. Read more...


Aim – To identify the underlying mechanisms of endometriosis and uterine fibroids and their associated symptoms to improve the outcome of affected women.

In the FENOX study, we aim to improve our understanding of the underlying mechanisms of endometriosis and uterine fibroids and their associated symptoms by means of longitudinal observation and laboratory analyses. To achieve this, samples and clinical data are collected from women undergoing surgery. These samples are used in state-of-the-art biomedical research to improve our understanding of the underlying biology of these symptoms in women with endometriosis and/or fibroids, which will lead to a better understanding of the conditions, tailored therapies, and the development of biomarkers for diagnosis and treatment. Read more…

Logo for the EndoCaRe Centre's FENOX Study.


There are a number of pain- and endometriosis-related patient organisations that are available to offer information, guidance and support.

Endometriosis UK offers a number of support groups through the UK and online. Support groups offer valuable support and information. Find out more about support groups and see upcoming support group meetings by clicking here.

In addition to support groups, Endometriosis UK runs a helpline to provide support and advice: 0808 808 2227Find out more about the helpline and the opening hours by clicking here. Because it may be difficult to talk to someone in person or over the phone, an online community is available with thousands of members sharing their experience of endometriosis on forums. Find out more about the online community by clicking here.

If you're in distress and need someone to talk to, you can call the Samaritans' 24 hour emotional support line in full confidence: 116 123.

Below is a selection of other organisations and useful links:

    Endometriosis Association

    World Endometriosis Research Foundation

    World Endometriosis Society

    The Endometriosis and Fertility Clinic

    International Pelvic Pain Society

    More Information

    NHS information on diagnosing and treating endometrios

    Bupa information on endometriosis

    British Medical Journal Best Practice guidance on endometriosis

    National Institute for Health and Care Excellence (NICE) guidance on the management of endometriosis

    Royal College of Obstetricians and Gynaecologists - Endometriosis Information Leaflet