There are many possible causes of heavy menstrual bleeding, such as a change of hormonal balance, fibroids and polyps, infections or bleeding disorders.
A change of hormonal balance occurs when the production of oestrogen and progesterone is not balanced. This is a common occurence among young women and also in the time leading up to menopause. This imbalance can also result from a wrong combination of hormone therapies.
Fibroids are mostly benign (non-progressive) tumours in the uterus, while polyps are incidents of endometrial overgrowth. Both can cause heavy menstrual bleeding, and may be removed if they are causing problems.
Infections of the uterus or cervix can be serious and include excessive blood loss. Infections are generally treated with antibiotics.
Abnormalities in blood coagulation (thickening of blood for blood loss to slow or stop) are serious disorders and medical treatment is necessary. If you think this is something you suffer from, speak to your doctor as soon as possible.