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Endometriosis (Part 1): When Menstruation Occurs In The Wrong Direction

Endometriosis is a painful condition that affects many women. It is an increasingly prevalent condition, especially among young women. In fact, studies have observed that females of Chinese ethnicity in Singapore were at a higher risk of getting endometriosis.

In this article, we will take a closer look at what causes endometriosis, its risk factors, symptoms, and diagnosis. For better understanding, we recommend checking out our earlier article on the menstrual cycle, if you haven’t already.

What is endometriosis and what causes it?

The endometrium is the innermost lining of the uterus. The luteal phase of the menstrual cycle marks the proliferation of the endometrium in order to create a suitable environment for implantation of the fertilized egg. If the egg is not fertilized, the endometrial tissue is shed in the form of bleeding, commonly known as menstruation or periods.

Endometriosis occurs when endometrial tissue is found to grow outside the uterus, in virtually any organ. Endometriosis most commonly affects the ovaries, but can also be found in other organs such as the fallopian tubes, vagina, cervix, vulva, intestines, bladder, pelvic cavity, etc.

Many theories have attempted to explain the possible mechanism by which endometrial tissue ends up in other organs. The most popular and accepted one is retrograde menstruation. As the name suggests, reverse/retrograde menstruation occurs when the endometrial tissue containing blood travels to the fallopian tubes, ovaries, and pelvic cavity, instead of flowing out of the vaginal canal, and sticks to the surfaces of the organs. Another theory suggests that endometrial tissue travels and implants via blood or lymphatic channels, similar to the way cancer cells spread. A third theory suggests that cells in any location transform into endometrial cells.

What are the risk factors of endometriosis?

The risk of retrograde menstruation is proportional to the number of menstrual cycles a woman goes through. The major risk factors for endometriosis are:

  • Early age of first period

  • Late menopause

  • Late or no pregnancy

  • Shorter and frequent cycles

  • Heavy and prolonged periods (>7 days)

  • Family history of endometriosis

  • Blockage or deformity of the reproductive tract/organs

From the risk factors, it can be deduced that the central idea is that continuous exposure to estrogen and the number of menstrual cycles play the biggest role in the development of ectopic endometrial tissue growth or endometriosis.

What are the signs and symptoms of endometriosis?

The signs and symptoms of endometriosis often coincide with the menstrual cycle, as the hormones estrogen and progesterone released during the menstrual cycle, are responsible for the growth, maintenance, and shedding of the endometrium.

Endometriosis exists on a spectrum and there are different stages (minimal, mild, moderate, and severe) of endometriosis depending upon location, size, number, and depth of the endometrial tissue being implanted. Hence, not every woman will experience the same symptoms. Some usually have a milder course with endometriosis, while others might develop debilitating symptoms.

That said, some of the most common signs and symptoms of endometriosis are as follows:

  • Painful periods (cramps or pain in the lower abdomen, most pronounced during the onset of periods)

  • Pain during sex

  • Painful urination

  • Painful bowel movements, diarrhea, or constipation

  • Heavy or prolonged periods

  • Difficulty conceiving

It's important to note that the amount of pain a woman experiences is not necessarily related to the severity of the disease. Some women with severe endometriosis may experience no pain, while others with a milder form of the disease may have severe pain or other symptoms.

How is endometriosis diagnosed?

As the disease often mimics and seems like cancer to a layperson, rapid and correct diagnosis by a doctor is crucial. The doctor would perform thorough checkup and pelvic exam. The doctor would also use the following imaging modalities to confirm endometriosis:

  • Transvaginal pelvic ultrasound: An ultrasound probe is inserted into the vaginal canal and used to create images through sound waves. Although it does not give a definitive diagnosis, it can detect the cysts of endometriosis (known as endometriomas), commonly found in the ovaries and other places.

  • CT or MRI scan: These are non-invasive diagnostic imaging procedures that can create high-resolution images of the organs. They can detect any abnormality that does not show up on regular x-rays, with high sensitivity and specificity.

  • Laparoscopic biopsy: During laparoscopy, a doctor inserts a laparoscope (a small tube with an attached camera) through a tiny incision on the abdomen. This allows the doctor to view inside the abdomen and look for endometrial implants, the extent of spread, and the organs affected. Small samples are collected and sent to a lab for examination. It may be possible to diagnose endometriosis without the need for a biopsy, but a laparoscopic biopsy remains the gold standard for diagnosis.

To know more about the treatment and long-term management of endometriosis, check out our next article. If you have any questions or wish to consult a doctor, feel free to reach out to us!



Kasper, D. L., et al. Harrison's principles of internal medicine (20th edition.). New York: McGraw Hill Education., 2018. (pg. 2798, 2812-2814) Ralston, Stuart H. Davidson’s Principles and Practice of Medicine. 23rd ed. Elsevier Health Sciences, 2018. (pg. 836-837)


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