What causes fibroids?

Fibroids (also known as uterine fibromyomas, leiomyomas or myomas) are non-cancerous growths or lumps of muscle tissue that form within the walls of the uterus (womb).

What are fibroids?

Fibroids can vary in size ranging from the size of a pea to the size of a rock melon or larger.

What causes fibroids?

It is not known exactly why fibroids occur. However, we do know the female hormones, oestrogen and progesterone play a significant role in stimulating the growth of fibroids.

Fibroids occur in women of reproductive age, growing at varying rates until the onset of menopause. After menopause, they tend to decrease in size and may slowly disappear. This is because at this time, the levels of oestrogen and progesterone decrease.

Some things increase your risk of getting fibroids, while others lower your risk including:

Higher risk Lower risk
  • Early onset of periods
  • Obesity
  • A family history of fibroids
  • Never having given birth
  • Being of Afro-Caribbean descent
  • Age (risk increases in your late reproductive years)
  • Having polycystic ovary syndrome (PCOS)
  • High blood pressure (hypertension)
  • Smoking
  • Having more than 2 children
  • Having had a multiple birth
  • Use of Depo-Provera (a contraceptive)
  • Use of the oral contraceptive pill

Fibroids occur in up to 70% of women by the time they are 50. Many women will not know they have fibroids because for the majority they do not cause symptoms.

Symptoms will depend on the size, number and location of the fibroids and may include the following:

  • Heavy or prolonged periods
  • Iron deficiency (anaemia)
  • Frequent urination
  • A pressure sensation on the bladder, bowel or back
  • Lower back pain
  • A lump or swelling in the abdomen
  • Period pain
  • Painful sex

In very rare instances, a fibroid may become cancerous and is called a sarcoma.

How are fibroids diagnosed?

Fibroids are usually found during a gynaecological examination, pelvic ultrasound or during surgery for other conditions.

Fibroids may be found during a hysteroscopy which is an internal examination, usually under general anaesthesia, performed using a hysteroscope (a thin telescope). This is inserted along the vagina into a woman’s uterus to examine the inside cavity.

Fibroids can also be found during a laparoscopy (keyhole surgery). This is an examination, using a thin telescope performed under general anaesthesia, through a small cut in the navel (umbilicus) to look at or operate on the pelvic organs, such as the uterus, ovaries and uterine (fallopian) tubes.

Impact on fertility

Infertility is not a common problem for women with fibroids, less than three per cent of women may have fertility problems as a result of fibroids.

Fibroids & pregnancy

Sometimes fibroids cause problems in pregnancy or they interfere with labour and delivery. The number and position of the fibroids will determine if there is a problem.

Fibroids can increase the risk of:

  • miscarriage
  • premature labour and delivery
  • the baby not being positioned with its head down and the crown presenting (malpresentation)
  • caesarean section because the fibroid obstructs the baby moving down into the birth canal
  • reduced placental flow because the fibroids put pressure on the placenta
  • severe bleeding after childbirth

A pregnancy following surgery to remove fibroids may increase the risk of the scar in the uterus rupturing during the pregnancy.

Management & treatment of fibroids

Most fibroids will not require treatment unless they are causing problems such as:

  • impairing fertility
  • period pain
  • heavy bleeding
  • pressure symptoms

Treatment will depend on:

  • the symptoms caused by the fibroid/s
  • whether the symptoms interfere with daily living
  • the position of the fibroid/s
  • the size of the fibroid/s

Treatments may include:

Treatment How it works
GnRH agonist (an artificial hormone used to prevent natural ovulation) It causes a temporary chemical menopause which shrinks the fibroids.
Intrauterine device (IUD) such as Mirena Placed in the uterus, it can reduce heavy periods.
Uterine artery embolisation
  • A fine substance or coil is injected into the uterine artery to reduce the blood supply to the fibroid causing the fibroid to shrink by 30-50%
  • The procedure is performed:
    • by a specialist radiologist using X-ray control
    • under sedation or anaesthesia
Endometrial resection A hysteroscope is used under general anaesthesia to cut out a fibroid that is partially or completely inside the cavity of the uterus, and partially in the wall of the uterus.  These are called ‘sub mucosal’ fibroids and they usually cause heavy periods.
Myomectomy Complete removal of a fibroid using:

  • laparoscopy (keyhole surgery)
  • laparotomy (an incision through the lower abdomen)
MRI–directed ultrasound technique Guided by an MRI, high intensity focused ultrasound waves cause a localised increase in temperature to destroy the fibroid.
  • Removal of some or all of the uterus particularly for multiple fibroids causing major symptoms
  • A hysterectomy is the only procedure that will permanently prevent fibroids from growing or recurring

A woman should make the decision to have a hysterectomy only after a discussion with her doctor about the reasons for the treatment, how it will be performed and the possible consequences. It is a treatment for women who no longer want to have children.

Who to see for help

If you are experiencing any of the symptoms of fibroids, see your doctor. Your doctor may refer you to a gynaecologist.

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