Cause Of Fibroids In Uterus and Fibroids: What to Know

September 13, 2025

Cause of Fibroids in Uterus and Fibroids: What to Know

Uterine fibroids (also called leiomyomas) are common, noncancerous tumors that grow in or on the muscular wall of the uterus. They can be as small as a seed or as large as a melon, and many people have them without knowing. Others experience heavy bleeding, pelvic pressure, pain, or fertility challenges. This guide explains what we know about the causes of fibroids, who is at risk, how they are diagnosed, and today’s most effective treatments.

What Causes Uterine Fibroids?

There is no single cause. Fibroids arise from a complex interaction of hormones, genes, and growth signals in the uterine muscle. Key drivers include:

Hormones (estrogen and progesterone): Fibroids have more hormone receptors than normal uterine muscle. They tend to grow during the reproductive years, may enlarge during pregnancy, and often shrink after menopause when hormone levels fall (NIH/NICHD).
Genetic changes: Many fibroids contain mutations (commonly in the MED12 gene) that make a single smooth muscle cell grow into a clonal tumor. These changes are found in the fibroid tissue itself and are not necessarily inherited (NIH).
Growth factors and extracellular matrix: Fibroids overproduce growth signals (e.g., TGF-β) and extracellular matrix (collagen), which can make the tissue stiff and promote growth.
Stem-like cells: A small population of cells in fibroids appears capable of self-renewal and may help sustain growth.

Importantly, fibroids are benign. They do not transform into cancer. A rare cancer called leiomyosarcoma can occur in the uterus, but it is usually not related to preexisting fibroids (ACOG).

Who Is at Risk?

Fibroids are extremely common—by age 50, the majority of women and people assigned female at birth will have them. Risk is influenced by:

Age: Most are diagnosed in the 30s and 40s, but fibroids can occur earlier.
Race: Black women are more likely to develop fibroids, to develop them at younger ages, to have more numerous and larger fibroids, and to have more severe symptoms (NIH; OWH/HHS).
Family history: Having a first-degree relative with fibroids increases risk.
Early menarche and lifetime estrogen exposure: Starting periods at a younger age and factors that increase estrogen exposure are associated with higher risk.
Body size: Higher body mass index is associated with increased risk—possibly because adipose tissue can influence estrogen levels.
Lifestyle and nutrition: Observational studies suggest low vitamin D levels and diets high in red meat may be linked with higher risk, while fruit and green vegetables may be protective. These associations are not definitive (NIH).

Fibroids are not caused by infections, sexual activity, or contraception. They can occur in anyone with a uterus.

Common Symptoms

Symptoms depend on the number, size, and location of fibroids:

Heavy menstrual bleeding (sometimes with clots), prolonged periods, or bleeding between periods
Anemia (fatigue, dizziness) due to chronic blood loss
Pelvic pressure or pain, lower back pain, or painful intercourse
Urinary frequency or urgency if fibroids press on the bladder; constipation if they press on the rectum
Reproductive effects: Some fibroids—especially those that distort the uterine cavity—can contribute to infertility, miscarriage, or complications in pregnancy (ACOG)

How Fibroids Are Diagnosed

A clinician starts with a history and pelvic exam. Imaging is often used to confirm size and location:

Ultrasound: First-line test; transvaginal ultrasound provides detail on uterine anatomy.
Sonohysterography: Saline-infused ultrasound can outline submucosal fibroids inside the cavity.
MRI: Helpful for surgical planning, complex cases, or when ultrasound is inconclusive.
Hysteroscopy: A small camera inserted into the uterus can directly visualize and sometimes remove fibroids inside the cavity.

Treatment Options

Management is individualized and depends on symptoms, fibroid characteristics, age, and goals for fertility. Many people with small or symptom-free fibroids can choose watchful waiting with periodic check-ins (ACOG).

Medications

NSAIDs (e.g., ibuprofen) can help pain but do not reduce bleeding volume.
Tranexamic acid reduces heavy menstrual bleeding during menses without affecting hormones.
Hormonal contraceptives (pills, patch, ring) and the levonorgestrel-releasing IUD can lighten bleeding and cramps.
GnRH agonists (e.g., leuprolide) and GnRH antagonists can temporarily shrink fibroids and reduce bleeding by lowering estrogen and progesterone. FDA-approved oral combinations include:
- Elagolix with add-back therapy (elagolix/estradiol/norethindrone acetate; brand Oriahnn) for heavy menstrual bleeding due to fibroids (FDA).
- Relugolix combination therapy (relugolix/estradiol/norethindrone acetate; brand Myfembree) for heavy menstrual bleeding due to uterine fibroids (FDA).
Because these lower estrogen, add-back estrogen/progestin is used to reduce side effects like hot flashes and protect bone; duration is typically limited per FDA guidance.

Medications help control symptoms but rarely eliminate fibroids. If symptoms persist or fertility is a goal, procedures may be considered.

Uterus-Preserving Procedures

Myomectomy: Surgical removal of fibroids, preserving the uterus. Approaches include hysteroscopic (inside the cavity), laparoscopic/robotic, or open abdominal surgery. It is the preferred option for many who want future pregnancy. Fibroids can recur over time (ACOG).
Uterine artery embolization (UAE/UFE): A minimally invasive radiology procedure that blocks blood flow to fibroids, shrinking them and relieving bleeding and pressure. Recovery is typically quicker than surgery, though data on fertility outcomes are mixed.
Radiofrequency ablation (RFA): Heat energy applied laparoscopically or transcervically (e.g., Acessa, Sonata) can shrink fibroids with short recovery; fertility data are growing but still limited compared with myomectomy.
MRI-guided focused ultrasound (MRgFUS): Noninvasive thermal ablation under MRI guidance for select candidates.

Definitive Treatment

Hysterectomy: Removal of the uterus is a definitive cure for fibroids and bleeding. It’s appropriate for those with severe symptoms who do not desire future pregnancy. Ovaries can often be preserved to maintain hormones (ACOG).

Fertility and Pregnancy Considerations

Not all fibroids affect fertility. Submucosal fibroids and large intramural fibroids that distort the uterine cavity are most likely to impact implantation or increase miscarriage risk. Myomectomy can improve fertility in selected cases. If you are pregnant with fibroids, most pregnancies are healthy, but there may be a higher risk of pain (degeneration), fetal malpresentation, or cesarean birth depending on size and location; close obstetric care is important (ACOG).

When to Seek Medical Care

Heavy bleeding that soaks pads/tampons hourly, lasts more than 7 days, or causes anemia symptoms (fatigue, dizziness)
Pelvic pain or pressure affecting daily life
Difficulty becoming or staying pregnant
Rapidly enlarging pelvic mass or fibroids that grow after menopause

A gynecologist can confirm the diagnosis and help match treatment to your goals and health history.

Myths and Facts

Myth: Fibroids turn into cancer. Fact: They are benign; leiomyosarcoma is rare and usually unrelated.
Myth: Only surgery helps. Fact: Many medications and minimally invasive procedures can control symptoms.
Myth: Birth control causes fibroids. Fact: Hormonal contraception often reduces bleeding and pain; it does not cause fibroids.

Can Fibroids Be Prevented?

There is no proven way to prevent fibroids. Maintaining a healthy weight, staying active, and ensuring adequate vitamin D may be helpful based on observational research, but more studies are needed. Regular check-ups can catch changes early and tailor management.

Trusted Resources and References

This article is for educational purposes and does not replace personalized medical advice. If you have symptoms or questions about fibroids, consult a qualified healthcare professional.