Uterine fibroids are common non-cancerous muscular growths that develop within or on the wall of the uterus. While many women have fibroids without symptoms, these growths frequently cause pain that is heightened during the menstrual cycle. The reason fibroids hurt specifically during a period involves mechanical, chemical, and hormonal events unique to shedding the uterine lining. Understanding these mechanisms helps explain why monthly discomfort can escalate into severe pain.
The Mechanism of Pain During Menstruation
Menstrual cramping, known as dysmenorrhea, is caused by the muscular contraction of the uterus expelling its lining. Fibroids distort the shape and increase the size of the uterus, forcing the muscle to contract more forcefully and sometimes for a longer duration. This intensified muscular effort results in the severe cramping often associated with fibroid-related periods.
Another driver of pain is the release of prostaglandins, hormone-like compounds produced when the uterine lining breaks down. Prostaglandins stimulate the uterine muscle to contract, but fibroids exaggerate this process in two ways. First, fibroids near the cavity increase the lining’s surface area, leading to greater prostaglandin production. Second, fibroids can increase inflammation within the uterine tissue, heightening sensitivity to these chemicals.
The bulk of the fibroids also contributes to pain through pressure and temporary swelling. During menstruation, increased pelvic blood flow causes congestion and fluid retention. This cyclical swelling can cause the fibroid tissue to become engorged, temporarily increasing its size and the pressure it exerts on surrounding nerves. This mechanical compression can turn a dull pelvic ache into sharp, period-specific pain.
How Fibroid Location Impacts Pain Severity
The type of pain experienced during the menstrual cycle is influenced by the fibroid’s location within the uterine structure. Fibroids are classified into three main types based on location, and each presents a distinct symptom profile. This explains why women with similar-sized fibroids may experience different menstrual symptoms.
Submucosal fibroids grow beneath the uterine lining, bulging into the cavity, and are linked to heavy menstrual bleeding (menorrhagia). These growths interfere with lining shedding, causing prolonged periods with large blood clots. The intense cramping results from the uterus contracting strongly to expel these large volumes of blood and tissue.
Intramural fibroids develop within the muscular wall of the uterus. These growths directly disrupt the muscle’s ability to contract uniformly, leading to severe, deep cramping (dysmenorrhea). As they expand, intramural fibroids make the uterus bulkier and more distorted, making the mechanical process of menstruation more difficult and painful.
Subserosal fibroids are located on the outer surface of the uterus, projecting toward the pelvic cavity. They typically cause less period-specific pain because they do not interfere with the uterine lining or muscular contractions. However, large subserosal fibroids can press on adjacent organs like the bladder or bowel. This pressure is exacerbated by the general congestion and swelling that occurs during menstruation.
The Hormonal Influence on Fibroid Pain
Uterine fibroid growth and activity are closely linked to the reproductive hormones estrogen and progesterone. Fibroids are hormone-dependent tumors because they contain more receptors for these hormones than normal uterine muscle cells. This dependence means fibroid symptoms, including pain, are most prominent during the reproductive years when hormone levels are high.
The monthly surge and subsequent drop in these hormones prime the fibroids to be more symptomatic. Estrogen promotes the growth and development of the fibroid tissue, contributing to its size and density. Progesterone also supports this growth, even though its primary function is preparing the uterine lining.
The cyclical peak of these hormones before the period can increase blood flow to the fibroids, making them more active or inflamed. When menstruation begins and hormone levels drop, the fibroids remain solid masses. This makes mechanical pain mechanisms, like forceful contractions and pressure, more severe in a uterus primed for growth and congestion.
Recognizing Symptoms That Require Medical Attention
While some increase in discomfort during menstruation may be manageable, certain fibroid-related symptoms indicate a need for professional evaluation. Pain that is so severe it regularly prevents you from participating in daily activities, such as going to work or school, should be discussed with a healthcare provider. This level of pain suggests the underlying mechanisms are significantly disrupting normal function.
The most common complication of fibroids is heavy bleeding, and this can lead to iron-deficiency anemia. Symptoms such as ongoing tiredness, general weakness, or lightheadedness are signs of anemia caused by excessive blood loss and warrant prompt medical attention. A healthcare professional can assess your iron levels and discuss options to manage the blood loss.
You should also seek immediate care if you experience sudden, severe, or sharp pelvic pain that is unrelieved by typical pain medication. This acute pain could signal a serious event, such as a fibroid outgrowing its blood supply and beginning to degenerate, or a pedunculated fibroid twisting on its stalk. Additionally, any pelvic pain that persists outside of the menstrual window, or bleeding that occurs between periods, should be evaluated to confirm the source of the symptoms.