Menstruation is the periodic discharge of blood, mucus, and tissues from the uterus associated with the cyclical phenomenon of ovulation. Menstruation is the epiphenomenum (an event caused by another and accompaning it) of the ovarian uterine cycles.

The human menstrual cycle involves a complex and regular change in female anatomy and physiology over an approximate monthly time period. This cycle commences at pubery and ceases at menopause. The average adult menstrual cycle lasts 28 days, with approximately 14 days in the follicular phase and 14 days in the luteal phase. It is less variable among women between the ages of 20 and 40, but more variable for the first 5-7 years after menarche (onset) and for the last 10 years before cessation of menses.

The first day of menstruation (or menses) represents the first day of the cycle (day 1). The cycle is then divided into 4 phases: follicular, ovulatory, luteal and menstrual. The follicular phase...