Uterine fibroids, also known as leiomyomas or myomas, are non-cancerous growths that develop from the muscle tissue of the uterus. These growths are common, affecting many women during their reproductive years. While some individuals remain unaware of their presence, others experience significant symptoms. The size of the fibroid is a major factor determining the patient experience and medical decisions.
Measuring and Classifying Fibroid Size
Healthcare providers measure fibroids using millimeters (mm) and centimeters (cm) through imaging techniques like ultrasound and Magnetic Resonance Imaging (MRI). Ultrasound is often the initial tool for detection, while MRI provides a detailed assessment of the fibroid’s size, number, and location within the uterus.
Small fibroids are generally considered less than 1 to 5 cm in diameter, comparable to a pea or a cherry. Medium-sized fibroids range from 5 cm to 10 cm, similar to a plum or a lemon. Fibroids exceeding 10 cm are classified as large and can grow to the size of a grapefruit or larger, sometimes causing the uterus to expand to a size equivalent to a second-trimester pregnancy. Physicians track the size of these growths over time in asymptomatic patients.
The Relationship Between Size and Symptoms
The physical mass of a fibroid often correlates with the presence and intensity of symptoms, as larger growths occupy more space. Large fibroids are more likely to cause “bulk symptoms” by pressing on nearby organs. Pressure on the bladder, for example, can lead to frequent urination or the feeling of incomplete emptying.
These larger growths can also distort the shape of the uterus, leading to pelvic pressure, heaviness, or discomfort in the lower abdomen. Distortion of the uterine cavity’s surface area by a large fibroid can contribute to heavy or prolonged menstrual bleeding, potentially leading to anemia. While a large fibroid is generally more likely to cause issues, the severity of the symptoms is not exclusively determined by size alone.
Why Location Matters More Than Just Size
While size is a factor, the specific position of a fibroid within the uterine wall often has a greater influence on the type and severity of symptoms. Fibroids are classified based on their location: submucosal, intramural, and subserosal.
Submucosal fibroids grow just beneath the inner lining of the uterus and bulge into the uterine cavity. Even a small fibroid (2 or 3 cm) can cause severe, heavy menstrual bleeding due to its direct impact on the uterine lining.
In contrast, subserosal fibroids develop on the outer surface of the uterus and expand outward. A subserosal fibroid can grow quite large (e.g., 8 cm) and cause only mild pressure or be completely asymptomatic, as it does not disrupt the menstrual cycle. Intramural fibroids, the most common type, are embedded within the muscular wall and tend to cause both bulk symptoms and heavy bleeding as they expand. Pedunculated fibroids are attached to the uterus by a stalk.
Treatment Decisions Based on Fibroid Size
The size of a fibroid plays a significant role in determining the appropriate treatment strategy, especially when combined with symptom severity and location. For small, asymptomatic fibroids, “watchful waiting” is typically recommended, as many fibroids grow slowly or shrink after menopause. Monitoring involves periodic imaging to track the fibroid’s dimensions and growth rate.
When fibroids cause persistent or worsening symptoms like heavy bleeding or pressure, intervention becomes necessary. Medium to large fibroids, or those causing significant distortion, are more likely to be treated with non-surgical or surgical methods. Non-surgical options, such as Uterine Fibroid Embolization (UFE) or medications that reduce bleeding, are often considered first. Surgical options, including myomectomy (removal of the fibroids) or hysterectomy (removal of the uterus), are reserved for larger fibroids, those that have failed other treatments, or when a definitive cure is desired.