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Endometriosis and pregnancy: What effect does it have?

Endometriosis & Pregnancy

Endometriosis and pregnancy are not a good combination.

Analysis of data1 obtained from the medical records of 14,655 women over a period of more than 30 years (between 1981 and 2010) led to the following conclusions:

Endometriosis is associated with a greater risk of miscarriage, in addition to greater development of complications during pregnancy. These risks include a 76% greater chance of spontaneous abortion and an almost three times increased likelihood of an ectopic pregnancy (where the egg implants in the fallopian tubes).

These results, published by a team led by Dr Lucky Saraswat, Consultant Gynecologist and Honorary Senior Lecturer at the University of Aberdeen, explain why endometriosis is considered as a significant fertility problem in women.

What is endometriosis?

The endometrium refers to the tissue that lines the walls of the uterus (womb). Endometriosis – not to be confused with endometritis – is a chronic illness caused by the growth of endometrial tissue in regions beyond the lining of the uterus; for example, in the ovaries or fallopian tubes. This problem is recognised by the Royal College of Obstetricians and Gynaecologists (RCOG)2 as having the potential to prevent pregnancy.

A diagram of endometriosis in the female reproductive organs (2014)3

It is estimated that endometriosis affects between 8-10% of women of reproductive age.4

Causes of endometriosis

There is no consensus on a single cause of endometriosis, though several theories exist:

  1. Retrograde menstruation theory Part of the menstrual tissue, rather than flowing outwards, goes backwards through the Fallopian tubes and adheres to the pelvic organs, where it continues to grow and becomes thicker over the course of time. However, this theory is widely debated: 90% of women experience reverse flow, but only around 10% develop endometriosis.
  2. Implantation in a surgical scar The possibility that, after performing surgery on a woman, such as a C-section, endometrial cells may adhere to the surgical incision.
  3. Immune system disorders Another explanation claims that the immune system is unable to identify the extrauterine endometrial cells as foreign. Therefore, it does not destroy them and allows them to grow outside of the uterus.

There is growing recognition of a number of factors that can increase the likelihood of an endometriosis pathology:

  1. High levels of oestrogen
  2. Having your first period at an early age
  3. Drinking alcohol
  4. Low Body Mass Index
  5. A family history of endometriosis
  6. Abnormalities in the uterus

Other experts, such as Dr Pere Barri, head of the multidisciplinary team which treats endometriosis patients at the Instituto Dexeus in Barcelona, suggest that certain environmental factors such as endocrine disruptors (chemicals that interfere with hormone systems), stress or unhealthy living habits can also lead to endometriosis.

Dr Barri believes that the triggers for endometriosis are introduced by modern lifestyles, pointing to the lack of occurrence of endometriosis in developing countries.

How does it affect fertility?

The presence of endometriosis does not necessarily mean that there will be a fertility problem – the interaction between endometriosis and pregnancy can be variable. The fertility implications depend on the degree of endometriosis presented by the patient.  Research shows that infertile women are 6 to 8 times more likely to have endometriosis than fertile women.5

In this regard, we can differentiate between different levels of impact it has and the relationship with the chances of getting pregnant.

  1. Minimal endometriosis (stage 1)
  2. Slight (stage 2)
  3. Moderate (stage 3)
  4. Serious (stage 4)


Symptoms suffered by people with this pathology are the following:

Pain during sexual activity

Painful menstruation. This pain is due to the release of prostaglandins which can lead to sharp contractions of the uterus

Reproductive problems. It is common for endometriosis to be suspected after a long period of unsuccessful attempts to achieve pregnancy

Heavy bleeding at menstruation (menorrhagia) and bleeding in between periods (menometrorrhagia)

It is also possible that other symptoms may be experienced, such as tiredness, diarrhoea, constipation, wind, or nausea, especially during menstruation


If you experience similar symptoms and suspect something may not be right, you should visit your GP/gynaecologist. They will assess the situation through a series of examinations:

Pelvic examination. The doctor will examine the area to look for possible abnormalities such as cysts in the reproductive organs, or scars. It is advisable to undergo this test during menstruation, as this is the time when the symptoms present.

Ultrasound or MRI. A scan is necessary during the diagnosis process.

Laparoscopy. This is a surgical procedure which requires general anaesthetic. The surgeon makes an incision close to the belly button and then inserts a fine instrument called a laparoscope (which gives the operation its name). This instrument is used to look for endometrial tissue outside of the uterus.

Possible treatment of endometriosis and pregnancy

If endometriosis is confirmed, you can choose between medical treatment or surgery.

Medical treatment involves treatment with medications that cause a decrease in the oestrogen in the body, preventing ovulation. These drugs prevent the growth of endometrial tissue and the production of ovarian hormones. Without stimulation by oestrogen, the affected regions will shrink; reducing their impact on your health. There are a number of these hormone treatments available, and the decision of which medication is suitable for you must be overseen by your clinician.

An alternative is surgery, but this is only advisable in cases where endometriosis is debilitating and leads to acute pain, or when the disease is in an advanced stage. The surgeon will surgically destroy or remove the endometriosis, as well as any scar tissue. This returns the reproductive organs to a relatively normal state. It has been observed that, after the operation, the likelihood of pregnancy increases considerably.

The most suitable procedure will depend on each case, as well as any personal circumstances such as age or the desire to have children.


  1. Saraswat, L, Ayansina, D, Cooper, KG, Bhattacharya, S, Horne, AW & Bhattacharya, S (2017), ‘Impact of endometriosis on risk of further gynaecological surgery and cancer: a national cohort study’ BJOG: An International Journal of Obstetrics and Gynaecology. DOI: 10.1111/1471-0528.14793
  3. staff (2014). “Medical gallery of Blausen Medical 2014”. WikiJournal of Medicine (2). DOI:10.15347/wjm/2014.010. ISSN 2002-4436.
  4. Rogers, Peter A W et al. (2009) “Priorities for endometriosis research: recommendations from an international consensus workshop” Reproductive sciences (Thousand Oaks, Calif.) vol. 16,4: 335-46.
  5. Bulletti, Carlo et al. “Endometriosis and infertility” Journal of assisted reproduction and genetics vol. 27,8 (2010): 441-7.

Further Information

Endometriosis UK

NICE Guidelines

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