The amount of blood women lose each month varies enormously from individual to individual. Some women lose a few teaspoonfuls and hardly notice their periods, whilst others lose enough blood to become anaemic (low blood count).  Because of this wide variation, it is impossible to define or describe a "normal" period or to know what is "abnormal" in terms of the amount, length, and frequency of bleeding.  What is heavy for one woman may be normal for others.  If your periods have changed and are causing you problems then they require investigation and appropriate treatment.

Doctors define menstrual bleeding as heavy (and call it menorrhagia) when more than 80mls of blood is lost during a period.  It is possible to measure menstrual blood loss but this is however, not practical.  Your perception of the heaviness of your period is as important as any clinical measurement. One of the signs that periods are heavy is when the blood clots. There is a simple explanation as to why large clots form. All blood contains a clotting factor.  To enable menstrual blood to flow freely from the womb and leave your body without clotting, the womb produces an anti-clotting agent. If the menstrual loss is very heavy, this agent will be used up before a period has finished, and any remaining blood will clot.

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