What causes heavy periods?

Diagnosing what causes heavy periods can sometimes be difficult. However, some physical condition affecting the uterus, such as fibroids and polyps, may cause heavy menstrual bleeding.

The more common reasons for heavy periods are:

  • fibroids
  • polyps
  • endometrial hyperplasia
  • endometrial cancer
  • adenomyosis.


Fibroids are abnormal growths that form in the muscle of the uterus. They are very common and can occur in up to 80 per cent of women. They are often referred to as ‘tumours’, but the vast majority are not cancerous.

Fibroids are more likely to cause symptoms if they are large, if there are many of them or if they push on your other internal organs. Some women with fibroids have very heavy menstrual bleeding, pelvic pressure or pain that interferes with their life, and some women have problems with fertility and pregnancy. However, fibroid symptoms tend to get better after menopause.

Fibroids can bulge from the inside or outside of the uterus. They can range in size from microscopic to the size of a grapefruit or even larger. Most fibroids are small and do not cause any symptoms at all.


Uterine polyps are usually non-cancerous (benign) growths of the lining of the uterus (the endometrium). They can also occur at the cervix. Polyps may cause heavy menstrual bleeding, bleeding between periods or bleeding after sexual intercourse. Occasionally, polyps can develop abnormalities, particularly in older women, so it is generally advised to remove them before they become dangerous.

Cancer, malignancy, and hyperplasia

Some women may develop an abnormally thick lining of the inside surface of their uterus. This condition is called endometrial hyperplasia and it may cause heavy menstrual bleeding, irregular bleeding or a bloodstained vaginal discharge. In some cases, endometrial hyperplasia may progress to endometrial cancer, a condition that is more common after menopause but can occur in younger women.

Women are at an increased risk of developing endometrial hyperplasia or endometrial cancer if they:

  • are over the age of 45 years
  • are over 90 kg in weight
  • have never had children
  • have a family history of endometrial, ovarian or bowel cancer
  • have polycystic ovarian syndrome
  • carry a gene that increases their cancer risk (such as HNPCC).


Adenomyosis is a common cause of painful and heavy periods, and can have the same symptoms as endometriosis and fibroids. It occurs when the endometrial glands grow into the muscle of the uterus. As a result, the uterus grows larger, and it can be tender when you are examined. However, it is not easily diagnosed because ultrasound, hysteroscopy, keyhole surgery and magnetic resonance imaging (the common approaches used) will not pick it up all of the time. Women tend to be in their 30s when they are diagnosed.

Other uncommon causes for heavy periods include:

  • an underactive thyroid
  • the use of anticoagulant drugs
  • some liver and kidney conditions
  • blood clotting disorders, for example Von Willebrand’s disorder
  • using hormone contraception such as the Pill or a prostestogen IUD.

Sometimes a reason for heavy periods is never found. In fact, for nearly half of all women with heavy periods all investigations will show that there is no obvious cause for their bleeding. This can happen at any age but is more common in women in their late thirties, which may mean that it is related to hormonal changes as women get older.


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