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Menstrual Cycle

The Menstrual Cycle

It's important to your health for you to know how your menstrual cycle works. It's even more important if you want to chart your fertility pattern to prevent pregnancy.

A menstrual cycle is the time from the first day of one period to the first day of the next. Some cycles are 21 days long. Some are 35 days long or longer. And some are somewhere in between. Each cycle is divided into two parts. One comes before ovulation. The other comes after. Here is the pattern for a 28-day cycle:

Part One — Day one is the day bleeding begins. It lasts from 3 to 5 days. Day seven is usually the day that some of the eggs in the ovaries start to get ripe. From Days 7 to 11, the lining of the uterus begins to get thick. After Day 11, hormones start working on the ripest egg to get it released from the ovary. Day 14, 15, or 16 is usually the day the egg is released (in a 28-day cycle).

Part One may last 13 to 20 days or more. How long it lasts is different for different women. For many women, how long it lasts is different from month to month. Simple changes in a woman's life can make Part One longer or shorter. For example, her regular pattern can change if she

  • becomes ill
  • works out very hard
  • has a lot of worries

Some women believe they can tell when the egg is released. Some have a slight pain in the back or on one side of the lower abdomen. This is called mittleschmerz — which is German for "middle pain." A few women may have a little blood tinged or clear discharge from the vagina. But none of these is a sure signal exactly when an egg has been released.

Part Two — The egg travels down the fallopian tube toward the uterus. It is usually in the tube that an egg joins with a sperm. Pregnancy begins if a fertilized egg travels through the fallopian tube to the uterus and attaches to the lining of the uterus. This is called implantation. The egg breaks apart in a day or two if this doesn't happen. Around Day 25, the hormones that could support a pregnancy drop off. This makes the lining of the uterus break down. It starts being shed in the woman's period a few days later on Day one. And a new cycle begins.

Part Two lasts from 14 to 16 days. It is about the same for all women.

Learn more about menstruation.

This information is not meant as a substitute for professional advice.

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