A recurring cycle that occurs monthly in women as the endometrium (lining of the uterus) thickens and prepares for pregnancy. If the egg released by one of the ovaries at ovulation (which occurs about midway through the cycle) is fertilized as it travels from the fallopian tube to the uterus, pregnancy occurs. If the egg is not fertilized, menstruation occurs: the blood-rich endometrium is shed, and the next month's cycle begins again.
The first day of menstrual blood flow is considered day 1 of the menstrual cycle.
The menstrual cycle is comprised of three phases: the follicular phase, ovulation, and the luteal phase.
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