Facts About Menstruation and Pain. Menstruation, also known as periods, occurs once a month, the lining of the uterus thickens in preparation for a fertilized egg - should the woman become pregnant. When that doesn't happen, that lining and a small amount of blood passes through the vagina. . Facts About Menstruation and Pain : Menstruation, or commonly known as periods, is the body's way of getting rid of what it doesn't need. Around once a
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