Skip to content
How It Works
Explore
Ask a Question Resources Pricing
Who It's For
Patients
Decode results, prep for appointments, weigh options.
Caregivers & advocates
Carry the research load for someone you love.
Providers & clinicians
Resources for patients in your practice.
Log In Ask a Question
PubMed This is a summary of 21 peer-reviewed journal articles Updated
Gynecology · Uterine Leiomyoma

Understanding Uterine Fibroids: Biology, Risk Factors, and Disparities

At a Glance

Uterine fibroids are noncancerous growths of uterine muscle that depend on hormones and may cause heavy bleeding, pelvic pain, pressure, or anemia. Their higher burden among Black women reflects complex biological, environmental, and healthcare factors.

Receiving a diagnosis of uterine fibroids can feel overwhelming, especially if you have been struggling with heavy periods or pelvic pain for a long time. It is important to know that you are not alone; fibroids are the most common non-cancerous tumors in women of reproductive age [1]. While they are technically “tumors,” they are benign (non-cancerous) growths of the uterine muscle [2]. Note that while fibroids are very common, conditions like postmenopausal bleeding or rapidly enlarging masses require careful medical evaluation for causes other than fibroids. Understanding the biology of these growths and the factors that influence them can help you feel more in control of your health journey.

The Biology of Fibroids

Uterine fibroids, also known as leiomyomas, develop from the smooth muscle cells of the uterus [3]. Research suggests they typically begin when a single muscle cell undergoes a genetic change and starts to divide uncontrollably, eventually forming a firm, rubbery mass [3][2].

A key feature of fibroids is that they are hormone-dependent, meaning they rely on estrogen and progesterone to grow [4][5]. This is why fibroids rarely appear before a person’s first period and typically shrink after menopause, when hormone levels naturally drop [2].

  • Progesterone’s Role: While estrogen was long thought to be the primary driver, modern research highlights progesterone as a major factor in fibroid growth [4][6]. Progesterone can trigger signaling pathways that tell fibroid cells to multiply [4].
  • Extracellular Matrix (ECM): Fibroids are not just made of cells; they also contain a large amount of structural material called extracellular matrix [7]. This material makes the fibroids stiff and contributes to the feeling of “bulk” or pressure in the pelvis [8].

Genetic Factors: The MED12 Connection

In many cases, the growth of a fibroid is linked to a specific mutation in a gene called MED12 [9].

  • What is MED12? This gene helps regulate how cells use genetic information to grow and function.
  • The Mutation: Research has found that between 50% and 80% of uterine fibroids contain a mutation in the MED12 gene [9]. This mutation promotes the muscle cells to grow into a fibroid [10].
  • Multiple Fibroids: It is common for a person to have multiple fibroids, and interestingly, each fibroid in the same uterus can have its own unique genetic mutation, suggesting they often start independently of one another [3].

Understanding Racial and Ethnic Disparities

Research has consistently shown that uterine fibroids do not affect all groups equally. Black women, in particular, face a significantly higher burden of disease [11].

Differences in Diagnosis and Burden

Statistics and estimates highlight a clear disparity in how fibroids manifest across different groups:

  • Higher Incidence: Black women are diagnosed with fibroids at an estimated rate that varies by study but has been reported as up to three times higher than that of White women [12].
  • Earlier Onset: Black women tend to develop fibroids at a younger age and are more likely to experience symptoms in their 20s or 30s [13][11].
  • Increased Severity: On average, Black women have more numerous and larger fibroids, leading to more severe pain and heavier bleeding [11][14]. This often results in a higher risk of anemia (low red blood cell count) due to blood loss [13].

Why Do These Disparities Exist?

Race itself is a social category, not a strictly biological cause. The reasons for these differences are complex and involve a combination of structural inequities, environmental exposures, and potential genetic factors [11][15].

  • Biological & Environmental Factors: Some research investigates differences in hormone processing or higher frequencies of certain genetic markers, though this only explains a piece of the puzzle and varies by study [15][16].
  • Systemic Healthcare Issues: Disparities are heavily driven by structural racism and inequities in the healthcare system [17]. Studies show that women of color often report negative interactions with providers, where their pain is underestimated or their concerns are dismissed [18][19].
  • Access to Care: Barriers such as differences in insurance coverage, lack of access to specialists who perform minimally invasive procedures, and historical mistreatment in gynecology can lead to delays in diagnosis and fewer treatment options being offered [18][17][20]. For example, Black patients are sometimes less likely to be offered minimally invasive surgeries (like laparoscopic options) compared to White patients with similar clinical needs [21].

Recognizing these disparities is a vital step toward advocating for yourself. You deserve a care team that listens to your goals—whether that involves preserving fertility, avoiding major surgery, or simply finding relief from debilitating symptoms.

Common questions in this guide

What are uterine fibroids, and are they cancerous?
Uterine fibroids, also called leiomyomas, are growths made from the smooth muscle and structural tissue of the uterus. They are benign, meaning they are not cancerous. Heavy bleeding, pelvic pain, or pressure can occur, but some people have few or no symptoms.
Why do uterine fibroids grow?
Fibroids depend on estrogen and progesterone, so they usually develop after the first period and often shrink after menopause. A genetic change in a uterine muscle cell can start a fibroid, and many fibroids contain changes in the MED12 gene. The structural material within a fibroid also contributes to firmness and pelvic pressure.
What does a MED12 mutation mean for a fibroid?
MED12 helps regulate how cells grow and function. Changes in this gene are found in about 50% to 80% of uterine fibroids and may help muscle cells multiply into a fibroid. Different fibroids in the same uterus can have different genetic changes.
Why are fibroids more common or severe among Black women?
Studies report that Black women may be diagnosed with fibroids more often, at younger ages, and with larger or more numerous growths; some estimates report incidence up to three times that of White women. Race itself is not a strictly biological cause, and the disparity reflects complex environmental, genetic, structural, and healthcare factors. Differences in pain recognition and access to specialists can also affect diagnosis and treatment.
Can heavy bleeding from fibroids cause anemia?
Yes. Heavy menstrual bleeding can cause blood loss that lowers red blood cell levels, leading to anemia. Ask your clinician whether blood tests should check your iron levels and screen for anemia, especially if your bleeding is heavy or persistent.
Are there uterus-preserving minimally invasive treatments for fibroids?
Some people may have minimally invasive or laparoscopic options that preserve the uterus, but the best choice depends on the fibroids’ size and location, symptoms, overall health, and fertility goals. Ask a gynecologist which options are available and why one is recommended over another. A specialist’s experience with similar symptoms and fertility goals can also be useful.
When should bleeding or a rapidly growing mass be evaluated?
Postmenopausal bleeding or a rapidly enlarging uterine mass should be evaluated by a healthcare professional rather than assumed to be caused by fibroids. Fibroids are benign, but these findings can have other causes that need careful assessment. Evaluation helps guide the right diagnosis and care.

Questions to Ask Your Doctor

Curated prompts to bring to your next appointment.

  1. 1.What is the estimated size and location of my fibroids, and how does that influence my symptoms?
  2. 2.Given my symptoms, have you checked my iron levels and screened for anemia?
  3. 3.Are there minimally invasive treatment options available to me that preserve my uterus?
  4. 4.Based on my age and medical history, what is the likelihood that my fibroids will continue to grow before menopause?
  5. 5.Can you explain why you are recommending this specific treatment over other available options?
  6. 6.Do you have experience treating patients with a similar clinical burden and goals for future fertility?

Questions For You

Tap a prompt to share your answer — we'll use it plus this page's context to start a tailored conversation.

References

References (21)
  1. 1

    A US population-based study of uterine fibroid diagnosis incidence, trends, and prevalence: 2005 through 2014.

    Yu O, Scholes D, Schulze-Rath R, et al.

    American journal of obstetrics and gynecology 2018; (219(6)):591.e1-591.e8 doi:10.1016/j.ajog.2018.09.039.

    PMID: 30291840
  2. 2

    UTERINE FIBROIDS.

    Bulun SE, Yin P, Wei J, et al.

    Physiological reviews 2025; (105(4)):1947-1988 doi:10.1152/physrev.00010.2024.

    PMID: 40214304
  3. 3

    Molecular and Cellular Insights into the Development of Uterine Fibroids.

    Machado-Lopez A, Simón C, Mas A

    International journal of molecular sciences 2021; (22(16)) doi:10.3390/ijms22168483.

    PMID: 34445194
  4. 4

    Wnt/β-catenin signaling pathway in uterine leiomyoma: role in tumor biology and targeting opportunities.

    El Sabeh M, Saha SK, Afrin S, et al.

    Molecular and cellular biochemistry 2021; (476(9)):3513-3536 doi:10.1007/s11010-021-04174-6.

    PMID: 33999334
  5. 5

    Current medical treatment of uterine fibroids.

    Sohn GS, Cho S, Kim YM, et al.

    Obstetrics & gynecology science 2018; (61(2)):192-201 doi:10.5468/ogs.2018.61.2.192.

    PMID: 29564309
  6. 6

    Subtype-Specific Tumor-Associated Fibroblasts Contribute to the Pathogenesis of Uterine Leiomyoma.

    Wu X, Serna VA, Thomas J, et al.

    Cancer research 2017; (77(24)):6891-6901 doi:10.1158/0008-5472.CAN-17-1744.

    PMID: 29055020
  7. 7

    Proteomic Profiling of Human Uterine Fibroids Reveals Upregulation of the Extracellular Matrix Protein Periostin.

    Jamaluddin MFB, Ko YA, Kumar M, et al.

    Endocrinology 2018; (159(2)):1106-1118 doi:10.1210/en.2017-03018.

    PMID: 29244110
  8. 8

    Mechanical Stiffness Influences the Response of Human Uterine Fibroid Cells to Hormonal Treatments.

    Bariani MV, Djibrila E, Maajid E, et al.

    Reproductive sciences (Thousand Oaks, Calif.) 2026; (33(1)):129-140 doi:10.1007/s43032-025-02016-0.

    PMID: 41359095
  9. 9

    The Mediator Complex Subunit 12 (MED-12) Gene and Uterine Fibroids: a Systematic Review.

    Amendola ILS, Spann M, Segars J, Singh B

    Reproductive sciences (Thousand Oaks, Calif.) 2024; (31(2)):291-308 doi:10.1007/s43032-023-01297-7.

    PMID: 37516697
  10. 10

    Oncogenic exon 2 mutations in Mediator subunit MED12 disrupt allosteric activation of cyclin C-CDK8/19.

    Park MJ, Shen H, Spaeth JM, et al.

    The Journal of biological chemistry 2018; (293(13)):4870-4882 doi:10.1074/jbc.RA118.001725.

    PMID: 29440396
  11. 11

    Racial disparities in uterine fibroids and endometriosis: a systematic review and application of social, structural, and political context.

    Katon JG, Plowden TC, Marsh EE

    Fertility and sterility 2023; (119(3)):355-363 doi:10.1016/j.fertnstert.2023.01.022.

    PMID: 36682686
  12. 12

    Uterine Fibroid Diagnosis by Race and Ethnicity in an Integrated Health Care System.

    Mitro SD, Dyer W, Lee C, et al.

    JAMA network open 2025; (8(4)):e255235 doi:10.1001/jamanetworkopen.2025.5235.

    PMID: 40172885
  13. 13

    Uterine fibroids with heavy menstrual bleeding stratified by race in a commercial and Medicaid database.

    Agarwal SK, Stokes M, Chen R, Lickert C

    AJOG global reports 2024; (4(4)):100412 doi:10.1016/j.xagr.2024.100412.

    PMID: 39559275
  14. 14

    Uterine Fibroids in Black Women: A Race-Stratified Subgroup Analysis of Treatment Outcomes After Laparoscopic Radiofrequency Ablation.

    Berman JM, Bradley L, Hawkins SM, Levy B

    Journal of women's health (2002) 2022; (31(4)):593-599 doi:10.1089/jwh.2020.9001.

    PMID: 34287028
  15. 15

    Multiomic analysis of uterine leiomyomas in self-described Black and White women: molecular insights into health disparities.

    Bateman NW, Abulez T, Tarney CM, et al.

    American journal of obstetrics and gynecology 2024; (231(3)):321.e1-321.e11 doi:10.1016/j.ajog.2024.04.051.

    PMID: 38723985
  16. 16

    Evidence that geographic variation in genetic ancestry associates with uterine fibroids.

    Keaton JM, Jasper EA, Hellwege JN, et al.

    Human genetics 2021; (140(10)):1433-1440 doi:10.1007/s00439-021-02322-y.

    PMID: 34302236
  17. 17

    Fibroids and health disparities: the COllaboration for EQuity in Uterine Leiomyomas specialized center.

    Stewart EA, Venable S, Borah BJ, et al.

    American journal of obstetrics and gynecology 2026; (234(6)):1623-1628 doi:10.1016/j.ajog.2025.12.068.

    PMID: 41534689
  18. 18

    Perceptions of Ethnoracial Factors in the Management and Treatment of Uterine Fibroids.

    Orellana M, Riggan KA, DSouza K, et al.

    Journal of racial and ethnic health disparities 2022; (9(4)):1184-1191 doi:10.1007/s40615-021-01059-8.

    PMID: 34013445
  19. 19

    The Effects of Oncologist Implicit Racial Bias in Racially Discordant Oncology Interactions.

    Penner LA, Dovidio JF, Gonzalez R, et al.

    Journal of clinical oncology : official journal of the American Society of Clinical Oncology 2016; (34(24)):2874-80 doi:10.1200/JCO.2015.66.3658.

    PMID: 27325865
  20. 20

    Income Inequities and Medicaid Expansion are Related to Racial and Ethnic Disparities in Delayed or Forgone Care Due to Cost.

    Clark CR, Ommerborn MJ, A Coull B, et al.

    Medical care 2016; (54(6)):555-61 doi:10.1097/MLR.0000000000000525.

    PMID: 26974677
  21. 21

    Uterine Weight as a Modifier of Black/White Racial Disparities in Minimally Invasive Hysterectomy Among Veterans with Fibroids in the Veterans Health Administration.

    Carey CM, Katon JG, Bossick AS, et al.

    Health equity 2022; (6(1)):909-916 doi:10.1089/heq.2022.0130.

    PMID: 36636115

This page is for informational purposes only and does not constitute medical advice about uterine fibroids. Your gynecologist can evaluate your symptoms, anemia risk, fertility goals, and treatment options.

Get notified when new evidence is published on uterine corpus leiomyoma.

We monitor PubMed for new peer-reviewed studies on this topic and email a short summary when something meaningful changes.