Uterine fibroids

What it is

Uterine fibroids are the most common benign tumors in women, estimated to affect 70–80% of women by age 50, though only 25–50% develop significant symptoms. Also called leiomyomas or myomas, fibroids are non-cancerous growths that arise from the smooth muscle tissue of the uterine wall (myometrium). They are estrogen- and progesterone-dependent: they grow during the reproductive years and typically shrink after menopause. In Canada, fibroids are among the leading indications for hysterectomy, making them a major driver of gynecologic surgical care.

Fibroids are classified by location, which largely determines the symptoms they cause:

Type	Location	Primary symptoms
Submucosal	Projects into the uterine cavity	Heavy bleeding, impaired fertility
Intramural	Embedded within the muscle wall	Bulk symptoms, pelvic pressure when large
Subserosal	Projects outward from the uterine surface	Pelvic pressure, urinary frequency
Pedunculated	Attached by a stalk (submucosal or subserosal)	Variable; risk of torsion

Even small submucosal fibroids can cause disproportionately heavy bleeding, while large intramural or subserosal fibroids tend to produce pressure and bulk-related symptoms.

Causes and mechanism

The exact trigger for fibroid development is not fully understood. Estrogen and progesterone are the primary growth drivers: fibroids express high levels of both hormone receptors, do not develop before puberty, and regress after menopause — a pattern consistent with hormonal dependency. Progesterone stabilizes the fibroid extracellular matrix, while estrogen promotes cell proliferation partly through growth factors such as IGF-1.

At the cellular level, most fibroids contain somatic (non-inherited) mutations in genes including MED12, HMGA2, and fumarate hydratase. Each fibroid likely originates from a single mutated smooth muscle cell, which is why multiple fibroids in the same uterus can have distinct genetic profiles.

Established risk factors include:

• African descent — Black women have significantly higher prevalence, earlier onset, and more severe disease; rates exceed 80% by menopause in this group
• Family history of fibroids
• Early menarche
• Nulliparity
• Obesity (adipose aromatase activity increases circulating estrogen)
• Diet high in red meat and low in green vegetables
• Vitamin D deficiency, which has been associated with higher fibroid prevalence and faster growth rates

Symptoms and diagnosis

Roughly half of women with fibroids have no symptoms at all. When symptoms occur, they depend on fibroid size, number, and location.

Common presentations include heavy menstrual bleeding (menorrhagia) — the most frequent complaint, particularly with submucosal fibroids — prolonged periods, pelvic pain or pressure, a sensation of lower abdominal fullness, urinary frequency from bladder compression, constipation from posterior fibroids, dysmenorrhea, and pain during intercourse. Heavy bleeding can lead to iron-deficiency anemia, which is a common reason Canadian patients first present to their family physician.

Submucosal fibroids that distort the uterine cavity can impair implantation and increase miscarriage risk. Large intramural fibroids may reduce IVF success rates.

Diagnostic workup:

1. Pelvic ultrasound — the primary tool; identifies fibroid number, size, and location. Available through LifeLabs, Dynacare, and hospital imaging across Canada.
2. MRI — more detailed mapping of fibroid location; used before surgery or uterine artery embolization (UAE).
3. Sonohysterography (saline infusion sonography) — introduces saline into the uterine cavity to better visualize submucosal fibroids.
4. Hysteroscopy — direct visualization of the uterine cavity; the gold standard for diagnosing and treating submucosal fibroids.
5. CBC and ferritin — to assess for anemia from heavy bleeding.

Treatment options

Treatment decisions depend on symptom severity, fibroid size and location, desire for future fertility, and proximity to menopause.

Watchful waiting is appropriate for asymptomatic or mildly symptomatic fibroids. Fibroids typically shrink after menopause, so observation is a reasonable strategy for women nearing that transition.

Medical management:

• Levonorgestrel IUS (Mirena) — reduces heavy bleeding effectively; does not shrink fibroids. Covered under most provincial drug benefit programs when prescribed for menorrhagia.
• Tranexamic acid and NSAIDs — reduce menstrual blood loss symptomatically.
• GnRH agonists (leuprolide, goserelin) — temporarily suppress estrogen, shrinking fibroids by 30–60%. Used short-term (3–6 months) before surgery to reduce fibroid size and correct anemia. Not suitable for long-term use due to bone density loss.
• GnRH antagonists (relugolix, elagolix) — newer agents that suppress estrogen more rapidly, typically used with low-dose add-back hormone therapy to limit bone and vasomotor side effects.
• Ulipristal acetate — a selective progesterone receptor modulator that reduces fibroid size and bleeding; Canadian availability has been restricted due to rare but serious liver safety concerns, and prescribers should check current Health Canada guidance before use.

Surgical and minimally invasive options:

• Hysteroscopic resection — gold standard for submucosal fibroids; preserves the uterus.
• Myomectomy — surgical removal of fibroids while preserving the uterus; can be performed hysteroscopically, laparoscopically, or by open surgery depending on fibroid characteristics.
• Uterine artery embolization (UAE) — a radiological procedure that cuts off blood supply to fibroids, causing them to shrink. Effective for bulk symptoms and bleeding; generally not recommended when fertility preservation is the primary goal.
• MRI-guided focused ultrasound (MRgFUS) — non-invasive ablation of fibroid tissue; availability in Canada is limited to select academic centres.
• Hysterectomy — definitive cure; reserved for women who have completed their family and for whom other treatments have not provided adequate relief.

When to see a clinician in Canada

Seek assessment from a family physician or gynecologist if you experience:

• Heavy periods that limit daily activities or are causing fatigue consistent with anemia
• Pelvic pain, pressure, or a persistent sense of abdominal fullness
• Urinary frequency or urgency without a confirmed infection
• Difficulty conceiving or recurrent miscarriages, particularly if a fibroid has already been identified on imaging
• Visible abdominal enlargement or a uterus that feels firm on self-examination

Referral to a gynecologist is typically required for surgical or minimally invasive options. In Canada, telehealth platforms such as Maple, Felix, Cleo, and others can facilitate initial assessment and referral coordination, though procedural management requires in-person specialist care. If you experience sudden severe pelvic pain or heavy vaginal bleeding, seek emergency care promptly — these can indicate fibroid degeneration or acute hemorrhage.

Limitations and open questions

Research is still emerging on several aspects of fibroid care. The mechanisms by which vitamin D deficiency promotes fibroid growth are not fully characterized, and clinical trials of vitamin D supplementation as a preventive strategy are ongoing. The long-term reproductive outcomes after UAE remain less well-defined than those after myomectomy, and current evidence does not support UAE as a first-line option for women who wish to conceive. Health Canada has issued safety advisories restricting ulipristal acetate use; clinicians and patients should consult current Health Canada guidance, as the regulatory status of this drug continues to evolve. Racial disparities in fibroid burden — Black women experience earlier onset, larger fibroids, and higher surgical rates — are well-documented but incompletely explained; socioeconomic access barriers in Canada likely compound biological risk factors. Finally, optimal long-term surveillance intervals for asymptomatic fibroids have not been established by Canadian clinical guidelines.