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Understanding the Normal Menstrual Cycle

Having a period (menstruation) is a normal, healthy part of being a woman. It’s also part of the menstrual cycle, a process that makes it possible for women to become pregnant.

It’s possible, though rare, for a woman to become pregnant during her period — especially if she has irregular cycles. A woman can become pregnant during irregular bleeding, which may not be a true period.

An Egg Is Released

Front view of uterus, fallopian tubes, and ovaries. Half has been cross sectioned to show inside. Vagina is opening to outside. Cervix is lower part of uterus connected to vagina. Two fallopian tubes lead from uterus to ovaries, one on either side of uterus. Ovaries have developing eggs inside. Uterus is lined on inside with endometrium. Eggs are female reproductive cells stored in the ovaries. During each cycle, 1 egg matures and is released from an ovary. This is called ovulation. The egg then travels from the ovary to a fallopian tube.

The Egg Travels Through a Tube

The egg moves through the fallopian tube toward the uterus. If sperm are present in the tube, the egg may be fertilized, resulting in pregnancy.

The Uterine Lining Grows Thicker

The lining of the uterus is made up of blood, tissue, and fluid. During each cycle, the lining thickens. This helps prepare the uterus to receive and nourish a fertilized egg. 

The Egg and Lining Are Shed

If pregnancy doesn’t occur, the egg and thickened lining of the uterus are no longer needed. They are then shed through the vagina. This is called a period.

How Long Is Each Cycle?

It is normal for a cycle to take 20 to 36 days. For teenagers, the time between periods might be more or less. For adults, it will be around a month from the first day of 1 period to the first day of the next. That’s why you may hear women talk about a “monthly cycle,” even though cycle length can vary from 1 month to another, and anywhere from 3 weeks to 5 weeks is normal. Not everyone has a 28-day cycle.  

How Long Does a Period Last?

It’s normal for a period to last 2 to 8 days. Talk to your doctor if your period lasts longer than 8 days for 2 cycles in a row.


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