The menstrual cycle is not the same for every woman. A normal menstrual cycle occurs about every 28 days and lasts about five days. On average, the menstrual flow is between 30–40ml of blood loss. Variation in the amount and duration of blood loss during a menstrual period is medically less significant than bleeding, pain, or discharge between periods.
Other types of abnormal uterine bleeding are too-frequent menstrual periods, bleeding between periods, and bleeding after menopause.
Vaginal bleeding may be something to worry about for women if it occurs post-menopause (over 50 years old). The risk of malignancy increases with age.
In a normal menstrual cycle, there is a balance between oestrogen and progesterone. These are hormones in the body that help regulate the build-up of the endometrium (uterine inner lining), which is shed each month during menstruation.
For menorrhagia, there may be an imbalance in oestrogen and progesterone levels. As a result of the imbalance, the endometrium develops in excess. When it is eventually shed, there is heavy menstrual bleeding. As hormone imbalances are often seen in adolescents and women approaching menopause, this type of menorrhagia is fairly common in these groups.