What are Fibroids?

Fibroids are non-cancerous growths that develop in or around the womb (uterus). The growths are made up of muscle and fibrous tissue, and vary in size. They're sometimes known as uterine myomas or leiomyomas.

Many women are unaware they have fibroids because they don't have any symptoms.

Understanding Fibroids

Fibroids are a mixture of smooth muscle cells and fibroblasts, which form hard, round, whorled tumours in the myometrium. The pathophysiology of fibroids remains unknown, although it is hypothesised that each fibroid is derived from a mutation in a single smooth muscle cell.

The uterus is the commonest site for fibroids. The location may have an effect on symptoms and quality of life. For example, submucous fibroids may lead to heavy menstrual bleeding and fertility problems and large fibroids may occupy two or more locations and can extend from the endometrial cavity to the serosal surface.

Why fibroids develop?

The exact cause of fibroids is unknown, but they have been linked to the hormone oestrogen. Oestrogen is the female reproductive hormone produced by the ovaries (the female reproductive organs). Increase in hormone oestrogen, and other sex steroid hormone, will influence the muscle and fibrous tissue to grow rapidly and spread from the myometrium. Fibroids usually develop during a woman's reproductive years (from around the age of 16 to 50) when oestrogen levels are at their highest. They tend to shrink when oestrogen levels are low, such as after the menopause when a woman's monthly periods stop.

Common symptoms of Fibroids

Heavy periods
Painful periods
Tummy (abdominal) pain
Lower back pain
Leg pains
Pelvic pain or mass
A frequent need to urinate
Constipation
Pain or discomfort during sex

Uncommon symptoms of fibroids

Complications caused by fibroids can affect pregnancy or cause infertility.

Who Gets Fibroids?

The prevalence of fibroids is estimated to be >70%. Common risk factors include:

Age: They most often occur in women aged 30 to 50
Race and ethnicity: Fibroids are thought to develop more frequently in women of African-Caribbean origin
Number of children (Parity): Women who have had children have a lower risk of developing fibroids, and the risk decreases further the more children you have
Weight: It's also thought they occur more often in overweight or obese women because being overweight increases the level of oestrogen in the body.
Dietary factors: Diet heavy in red mean is associated with a 70% increased risk of fibroids. Green vegetables, fruits, and dairy decrease the risk of fibroids.
Family history: Genetics has a role in fibroid formation. If your mother or sister had fibroids, you are at an increased risk of developing them.

What controls the growth of fibroids?

Oestrogen and progesterone control the proliferation and maintenance of uterine fibroids, and most medical treatments act by inhibiting the production of sex steroids or their action. The primary action of oestrogen is thought to be mediated through induction of progesterone receptor expression, thereby allowing leiomyomas to respond to progesterone. Hormonal replacement therapy may cause some growth of fibroids, but this is of uncertain clinical importance.

DIAGNOSING FIBROIDS

Fibroids are diagnosed through imagine (ultrasonography, X-ray, MRI), histological evaluation and biochemical laboratory evidence. Sometimes surgery is needed to confirm the diagnosis.

Fibroids are common, and with the widespread availability of high resolution ultrasonography, they are often diagnosed incidentally.

Women presenting in primary care with symptoms suggestive of fibroids should have their gynaecological history evaluated, including cervical screening, and should undergo a pelvic examination for any masses, a haemoglobin estimation to check for iron deficiency anaemia, and, if urinary symptoms are present, midstream urine testing to exclude a urinary tract infection. Diagnostic uncertainty, association with problematic symptoms, or any clinical or radiological suspicion of malignancy should prompt referral for further investigations. Women with asymptomatic fibroids, if the diagnosis is certain, often do not need further investigation or treatment.

Types of fibroids

Fibroids can grow anywhere in the womb and vary in size considerably. Some can be the size of a pea, whereas others can be the size of a melon.

The main types of fibroids are:

Intramural fibroids are the most common type of fibroid, which develop in the muscle wall of the womb
Subserosal fibroids develop outside the wall of the womb into the pelvis and can become very large
Submucosal fibroids develop in the muscle layer beneath the womb's inner lining and grow into the cavity of the womb

In some cases, subserosal or submucosal fibroids are attached to the womb with a narrow stalk of tissue. These are known as pedunculated fibroids.

Left: An MRI axial or cross sectional scan.

Right: An MRI sagital view of the pelvis.

An MRI gives clinicians a reproducible, detailed picture of how many fibroids there are, how big they are and exactly where they are located. Not all women with fibroids need an MRI. All patients that are being evaluated for a uterine artery embolization will get an MRI.

Treating fibroids

Fibroids that don't cause symptoms often don't require treatment and may shrink naturally, especially after menopause. If symptoms do occur, treatment usually begins with medication to manage them or shrink the fibroids.

If medication is ineffective, surgical or minimally invasive options may be considered. Treatment is generally only needed for fibroids larger than 3 cm that cause heavy bleeding or affect quality of life.

The choice of treatment depends on whether preserving fertility or the uterus is a priority. Options range from observation and medication to radiological or surgical interventions, including hysterectomy.

Hysterectomy is the most definitive treatment but is irreversible and more invasive. Standard treatments for heavy menstrual bleeding may help, though they're less effective when fibroids are present.

Treatment type	Advantages	Disadvantages
Medical treatment:
Tranexamic acid/mefenamic acid	Reduced heavy menstrual bleeding in women without uterine fibroids; improves health related quality of life	Efficacy in presence of fibroids is unknown
Levonorgestrol releasing intrauterine system	Treatment of choice for heavy menstrual bleeding in absence of fibroids; provides contraception	Evidence of usefulness in presence of fibroids is limited; cannot be used if uterine cavity is distorted by fibroids; high expulsion rate with submucosal fibroids
Selective progesterone receptor modulators	Reduces heavy menstrual bleeding and shrinks fibroids; does not cause menopausal side effect or bone demineralisation; licensed for preoperative use to shrink fibroids and for intermittent long term use	Can cause unscheduled bleeding in women with submucous fibroids; is associated with endometrial changes that are not yet fully understood
Mifepristone	Can reduce bleeding and pressure symptoms for up to six months; reduces heavy menstrual bleeding and improves fibroid related quality of life	Uncertain effect on fibroid volume
Gonadotrophin releasing hormone agonists	Can be used for 3-6 months presurgery to reduce uterine size, fibroid size, and perioperative blood loss; leads to amenorrhoea and helps correct iron deficiency anaemia; menopausal side effects can be minimised by the use of “add back” hormone replacement therapy	Long term therapy beyond six months can reduce bone density; vasomotor and other menopausal symptoms are common; more commonly initiated in secondary care, although continuation may take place in primary care
Radiological and surgical
Uterine artery embolisation	Performed under local anaesthesia (no general anaesthestic required); requires overnight stay in hospital; similar success rates and satisfaction rates to surgery; global uterine fibroid treatment; quick recovery; decreases fibroid size and menstrual blood loss; conserves uterus	Post-procedure pain can be severe and variable; alleviation of symptoms can take up to six months; risk of fibroid expulsion; higher rate of early re-intervention compared with surgery; impact on fertility and pregnancy is uncertain
Myomectomy	Conserves uterus; helps resolve bulk symptoms; can also be performed laparoscopically or	Insufficient evidence regarding role in improving infertility to conclude that it is best treatment; associated with major surgical risks; risk of fibroid regrowth; not a global uterine fibroid treatment; although morcellation of fibroids is possible at laparoscopic myomectomy, there are concerns about this treatment
Hysterectomy	Well established effective procedure to permanently resolve fibroid symptoms; cost effective with high patient satisfaction rates; vaginal and minimally invasive laparoscopic approach to this procedure is suitable in selected cases; global uterine fibroid treatment and only treatment that prevents recurrence; higher patient satisfaction rates than with uterine artery embolisation	Is associated with procedure related morbidity and mortality, whatever approach is used; higher surgical complication rates when associated with large fibroids; not suitable for women wanting to preserve fertility

I HAVE ENDOMETRIOSIS AND AM TRYING TO GET PREGNANT

If you have been diagnosed with endometriosis and are trying to conceive, there is still a good chance of achieving a successful pregnancy naturally. However, if you do have problems conceiving it may be helpful to consult a fertility or endometriosis specialist.

They can perform a comprehensive assessment of both partners, which may include hormone and ovarian reserve blood tests, semen analysis, imaging or procedures to check if the fallopian tubes are open and functioning properly.

Depending on the findings and individual circumstances (such as age, severity of endometriosis, and how long you’ve been trying) fertility treatment may be recommended.

👉 Learn more about fertility treatments.

ARE THERE STUDIES I CAN BE INVOLVED IN?

Are you interested in making a real difference for those living with fibroids? We're leading vital research to better understand this condition and discover more effective treatments.

Volunteer for one of our clinical studies to play a direct role in advancing science and improving lives.

👉 Visit our Clinical Research Studies page

Patient support and Information

The Lake Foundation: A UK charity that aims to improve the health of the African and African-Caribbean community through health promotion, early detection, research and support

British Fibroids Trust: A charitable organisation that provides information on fibroids and treatment options, provides a platform for women to exchange their experiences

Related patient pages

What is Endometriosis?

Endometriosis affects an estimated 176 million women around the globe, causing many to suffer a life of pain and debilitation and sometimes infertility.

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FENOX research study

FENOX is a prospective study that aims to improve our understanding of the underlying mechanisms of endometriosis and uterine fibroids and their associated symptoms by means of longitudinal observation and laboratory analyses.

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Other WRH research projects

WRH comprises over 30 cutting-edge research groups spanning five core themes, each led by world-renowned experts in their respective fields. Many of these groups collaborate with other departments at the University of Oxford, as well as with universities and business partners globally.

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