Endometriosis is a condition in which the endometrial tissue that usually lines the inside of the uterus develops elsewhere in the body.

The exact cause of endometriosis is not well understood, but multiple factors are thought to contribute to its development.

Retrograde menstruation, also known as Sampson’s theory, is one widely discussed opinion about the cause of endometriosis. It refers to the flow of menstrual blood back through the fallopian tubes, which connect the uterus to the ovaries, and into the pelvic cavity. Retrograde menstruation occurs to some degree in almost all women, but only a few develop endometriosis. So, more research is needed to understand whether retrograde menstruation is a cause of endometriosis.

The normal menstrual cycle

Each month the endometrium or the lining of the uterus becomes thicker and richer in blood vessels in preparation for a possible pregnancy. Then an egg is released from the ovaries. This is known as ovulation. In case of no pregnancy, the menstrual period occurs 14 days later, during which the body sheds the endometrium. The menstrual blood flows through the cervix, the connection between the uterus and the vagina, and exits the body.

Retrograde menstruation

During retrograde menstruation the menstrual blood does not flow through the cervix and vagina, but instead moves backward through the fallopian tubes into the peritoneal cavity (the area within the abdomen where the intestines, stomach, and liver are located). Contraction of the uterine muscle wall in non-pregnant women — called uterine peristalsis — is thought to play a role in retrograde menstruation.

According to Sampson’s theory, the endometrial cells that are carried together with the blood then can stick to the pelvic walls and surfaces of pelvic organs. The endometrial tissue then grows and thickens during each menstrual cycle. Unlike normal endometrium that can leave the body, these implants cannot exit the body and form lesions causing inflammation and pain.

Arguments against the theory of retrograde menstruation

Retrograde menstruation is a process that occurs in many women, and most of them never develop endometriosis. According to some experts, if retrograde menstruation caused endometriosis, the condition would have to be more common.

Also, if the theory of retrograde menstruation was true, the severity and extent of the disease would subsequently increase with age, which is not the case.

Insead, experts think that genetics or other factors predispose women to develop endometriosis. In these predisposed women, retrograde menstruation might play a role in triggering the development of endometriosis, but is not the root cause of the disease.


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