There are many reasons why women can have heavy periods. If periods are very heavy from the time you start having them and you get very anemic on a regular basis because of this, you may have a hereditary clotting factor deficiency. The most common one is Von Willibrands disease. As many as 50% of young girls who present with very heavy bleeding upon beginning their periods and need to be hospitalized and receive a blood transfusion for it have von willibrands disease.

In the teens and twenties it is common to have 'dysfunctional uterine bleeding' as a cause of heavy bleeding. Hormonal imbalances and having an immature hypothalamic pituitary axis (mixed signals being sent from hypothalamus and pituitary in the brain to the ovaries and uterus) are common. Miscarraige and pregnancy loss, whether recognized or unrecognized, are a common cause of heavy bleeding regardless of age.

As women enter their 30s and 40s fibroids (benign muscle tumor of the uterus), adenomyosis (endometrial glands that bleed in the muscle of the uterus), endometrial polyps, hormonal issues, endometrial hyperplasias (overgrowth of tissue in the lining of the uterus due to extra estrogen production or administration) and rarely endometrial cancers can occur and present with heavy menses.

Perimenopausal women in their late 40s and 50s can present with heavy periods due to structural problems such as fibroids, endometrial polyps or adenomyosis, or functional problems such as hormonal imbalances. Hyperplasias, precancers and cancers of the uterus must be ruled out, especially as women get older.