Uterine fibroids (leiomyomas) are non-cancerous growths that develop within or on the muscular wall of the uterus. These tumors consist of smooth muscle cells and fibrous connective tissue, varying significantly in size from tiny masses to large, bulky structures. Fibroids are remarkably common, with estimates suggesting that between 20% and 80% of women will develop them by the age of 50. The presence of these growths can often lead to various symptoms, most notably heavy or prolonged menstrual bleeding.
The Direct Answer: Fibroids Do Not Shed
The definitive answer to whether fibroids shed during a period is no. Menstruation involves the monthly shedding of a specific layer of tissue, and fibroids are not composed of this material. The lining of the uterus is the endometrium, a dynamic layer designed to thicken in preparation for a potential pregnancy. When pregnancy does not occur, the functional layer of the endometrium breaks down and is shed as the menstrual flow.
Fibroids originate from the myometrium, the thick, muscular wall of the uterus that surrounds the endometrium. This muscle tissue does not participate in the cyclical process of breakdown and shedding. The myometrium provides the structural integrity of the uterus; fibroids are tumors of this permanent muscle layer. Therefore, the tissue that forms a fibroid is structurally distinct from the temporary lining that is expelled during a normal menstrual cycle.
The myometrium remains intact throughout the menstrual cycle, contracting only to help expel the menstrual flow or during labor. The fibroid mass, being an integral part of this muscle wall, simply cannot detach and pass out of the body like the endometrial tissue. This fundamental difference in tissue origin explains why a fibroid itself does not “shed.”
How Fibroids Cause Heavy Menstrual Bleeding
While fibroids do not shed, they frequently cause excessive or prolonged menstrual bleeding (menorrhagia). This heavy bleeding is often why people mistakenly believe the fibroid is shedding. One mechanism involves the physical distortion of the uterine cavity, particularly by submucosal fibroids that project inward. This alters the surface area of the endometrium, which can lead to a greater volume of tissue being shed each month.
Another factor is how fibroids affect the uterus’s ability to control bleeding. Normally, the myometrium contracts after the endometrium sheds to clamp down on blood vessels and stop the flow. Fibroids disrupt this organized muscle contraction, which impairs the uterus’s ability to effectively constrict the blood vessels. This lack of proper contraction results in longer, heavier bleeding.
Fibroids also influence the local blood supply. They can promote a process called angiogenesis, which is the formation of new blood vessels, resulting in an irregular and fragile vascular network surrounding the tumor. These abnormal vessels are prone to rupture and leakage, contributing significantly to the heavy blood loss during menstruation.
Furthermore, fibroids can impact the hormonal environment and signaling within the endometrium. They may cause a local imbalance that disrupts the normal development and breakdown of the uterine lining. This interference can lead to an overly thick or disorganized endometrium, which naturally results in a larger amount of tissue and blood to be expelled during the period.
Understanding Fibroid Expulsion
The confusion between shedding and heavy bleeding often stems from a separate, rare event called fibroid expulsion. Expulsion is the process where an entire fibroid, or a piece of one, detaches from the uterine wall and is forcefully passed through the cervix and vagina. This is not a normal part of the menstrual cycle but a spontaneous or induced event, most common with pedunculated submucosal fibroids.
Expulsion typically begins when the fibroid loses its blood supply, often due to torsion or degeneration, causing the tissue to die. The uterus then recognizes the necrotic fibroid as a foreign body and attempts to push it out through strong, labor-like contractions. This process can be intensely painful and is often accompanied by significant bleeding and the passing of solid, non-blood tissue.
Expulsion can occur naturally, sometimes seemingly during a heavy period, or it may be triggered following certain medical procedures designed to cut off the fibroid’s blood flow, such as uterine fibroid embolization (UFE). If a woman believes she is passing a fibroid (which may appear as dark, clotted tissue fragments), prompt medical evaluation is required. If the fibroid does not fully detach, a procedure may be necessary to safely remove the remaining tissue and prevent infection.