When menstrual bleeding is heavy, clotting can also occur. Large clots can be extremely painful and cause cramping as they pass through the cervix. All blood contains a clotting factor. To enable menstrual blood to flow freely from the uterus without clotting, the uterus produces an anti-clotting agent. But if the menstrual loss is heavy, it is possible that the anti-clotting agent will be used up before a period has finished, so that the remaining blood is likely to form clots. If they are large.. it should be brought to your doctors attention as well.
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