A muscle of the uterus, the myometrium is considered the most powerful in the female body. It is he who, by his contractions, allows the evacuation of the rules or the expulsion of the baby at childbirth.

The lining of the uterus is made up of two layers: the endometrium, the lining that lines the internal cavity of the uterus, and the myometrium. Between the two, there is a fine junction area.

During menstruation

At the end of the menstrual cycle, the levels of estrogen and progesterone secreted by the ovaries drop, which triggers menstruation, which is the bleeding and scaling of the endometrium. The myometrium responds by contracting, which makes it easier for blood, unfertilized egg and loose mucous membranes to escape. These contractions are more or less painful.

During childbirth

During pregnancy, the myometrium is under the influence of progesterone. Produced by the placenta, this hormone inhibits its contractions and promotes its relaxation, which allows it to stretch enough to accommodate the fetus. But the action of progesterone is countered by another hormone: estrogen, the level of which increases during pregnancy. When labor begins, at the end of the 9th month, the myometrium is once again able to contract powerfully.

The mechanisms behind the spontaneous onset of contractions is still poorly understood, but it is known that it involves several hormones:

• estrogen, which facilitates uterine contractions by countering the effects of progesterone, but also by stimulating the creation of new oxytocin receptors on the cells of the myometrium, and by promoting the synthesis of prostaglandins by the placenta;
  
• oxytocin, released into the blood by the pituitary glands of the mother and the fetus, sees its level increase during pregnancy, at the same time as the number of its receptors on the myometrium. Its action in strengthening uterine contractions is therefore at its maximum at the time of childbirth;
• prostaglandins, the level of which also increases at the end of pregnancy, also play a role in strengthening contractions, since they stimulate the release of calcium, a contraction-activating mineral, in the myometrium cells. 

The start of work could also be explained by mechanical reasons. At the end of pregnancy, the fetus presses more and more on the bottom of the uterus, pulling on the fibers of the myometrium, which are already very distended. This increases the muscle’s propensity to retract, and therefore to contract.

Uterine fibroma

Very common, uterine fibroma is a benign tumor. The majority of affected women do not experience any symptoms. But some patients suffer from severe and sudden pain during menstruation (dysmenorrhea), long and heavy periods (menorrhagia), bleeding between periods (metrorrhagia) and / or fertility problems. Other symptoms are also possible, such as pressure or heaviness in the lower abdomen, frequent urge to urinate, constipation, painful intercourse, etc. In pregnancy, fibroids also increase the risk of miscarriage and premature delivery.

Adenomyosis

Usually defined as endometriosis internal to the uterus, adenomyosis corresponds to an infiltration of endometrial cells into the myometrium. This pathology is common and benign, but it can lead to menorrhagia, dysmenorrhea and metrorrhagia. It is also found in many infertile women: the inflammatory reaction of the myometrium would prevent the implantation of the embryo, and would double the risk of miscarriage.

Some cancers

Uterine sarcomas, which start in the myometrium, are relatively rare. On the other hand, it can happen that endometrial cancer goes undiagnosed to tend and progress to a more invasive form: the lesion can then extend into the muscle. 

In order to be taken care of in time, as there is no systematic screening for cancers of the body of the uterus, abnormal bleeding (after menopause, in particular), pelvic pain and / or abdominal heaviness must you get them to see your gynecologist.

In case of uterine fibroid or adenomyosis

The treatments are not systematic. They are mainly aimed at reducing symptoms and improving the chances of pregnancy. It could be :

• medication, most often;
• a progesterone IUD, if there is no immediate desire for pregnancy, to reduce the amount and duration of periods;
• embolization of the arteries which irrigate the fibroids, to asphyxiate them. This minimally invasive technique consists of injecting microbeads into these vessels using a catheter;
• a myomectomy, that is to say a surgery to remove one or more fibroids, if they are numerous or large;
• a hysterectomy, or complete removal of the uterus, but only as a last resort, and if the patient has no more plans to have a baby.

In case of confirmed cancer of the myometrium

As the risk of recurrence and metastasis is high, hysterectomy is very frequently performed in the event of a cancerous lesion affecting the myometrium. It is combined if necessary with other treatments (removal of the ovaries and tubes, radiotherapy, chemotherapy, hormone therapy, etc.). It depends on many parameters: type of cancer, stage, progressive risks, etc.

The detection of abnormalities of the myometrium is most often done via a pelvic ultrasound. Other examinations are sometimes necessary, in addition, to establish and clarify the diagnosis: magnetic resonance imaging (MRI), hysteroscopy (introduction of a small camera into the uterus), an endometrial biopsy, a thoraco-abdomino-pelvic scanner, etc.