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Quick Facts

Menstrual Cycle

By

The Manual's Editorial Staff

Last full review/revision May 2020
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What is a menstrual cycle?

A menstrual period (menstruation) is the monthly bleeding from the vagina that occurs at the beginning of each menstrual cycle. During menstruation, the lining of the uterus comes off and is released as menstrual blood.

  • An egg matures and is released (a process called ovulation)

  • The lining of the uterus swells up with blood vessels so it's ready to accept an egg that has been fertilized by a man's sperm

  • A fertilized egg attaches to the lining of the uterus and starts growing OR

  • The egg doesn't get fertilized, so it doesn't attach, and the lining of the uterus comes off and is released as menstrual blood

The days of a menstrual cycle are counted from the first day of one menstrual period to the start of the next menstrual period. A menstrual cycle usually lasts between 25 and 35 days but can vary from month to month. Usually, a menstrual period lasts 3 to 7 days.

What can go wrong with a menstrual cycle?

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