The menstrual cycle is the body's monthly pattern of preparing for a possible pregnancy. The lining of the uterus (endometrium) starts to thicken. One of the ovaries releases an egg. And then, if the egg isn't fertilized or a fertilized egg doesn't attach to the lining of the uterus (implant), the endometrium sheds from the uterus as a menstrual period.
Menstrual phase (period).
The thickened lining of the uterus (endometrium) is shed, causing menstrual bleeding. Day 1 of the cycle is the first day of menstrual bleeding. Bleeding usually lasts for 4 to 6 days.
The lining of the uterus thickens. Also, inside a sac (follicle) on the surface of an ovary, an egg becomes ready to be released.
The egg is released (ovulation). Ovulation days can range from about day 7 to day 22 of the cycle. But for each person, the ovulation day is often on the same day each cycle.
If the egg is fertilized by sperm, it may attach to (implant in) the lining of the uterus, and pregnancy begins.
If the egg is not fertilized or a fertilized egg does not implant, the lining of the uterus is shed during the menstrual period. Then the cycle starts again.
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