Understanding the Normal Menstrual Cycle

Irregular cycles

If you have irregular cycles, you can become pregnant during bleeding. This may not be a true menstrual period.

An egg is released

Eggs are female reproductive cells stored in the ovaries. During each cycle, the hormones trigger an egg, (usually one), to mature and be released from an ovary. This is called ovulation. The egg then travels from the ovary to a fallopian tube. Pregnant and menopausal women do not ovulate.

Some women feel a dull pain on one side of the lower abdomen during the time of ovulation.

The egg travels through a tube

The egg moves through the fallopian tube toward the uterus. An egg lives for just 12 to 24 hours after ovulation. If sperm are present in the tube, the egg may be fertilized, and pregnancy could result.

The uterine lining grows thicker

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

The egg and lining are shed

If pregnancy doesn’t happen, the unfertilized egg and the thickened lining of the uterus are no longer needed. So the hormone levels drop and the extra tissue lining the uterus is shed through the vagina. This is called a menstrual period.

How long is each cycle?

It's normal for a cycle to take 21 to 34 days. For teens, the time between periods might be as much as 45 days. For adults, it will be around a month from the first day of one period to the first day of the next. That’s why you may hear about a “monthly cycle,” even though cycle length can vary from 1 month to another, and anywhere from 3 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 7 days. Talk with your health care provider if your period lasts longer than 7 days for 2 cycles in a row.