The menstrual cycle

What is the menstrual cycle?#

The menstrual cycle is a natural but complex series of changes that your body goes through each month to prepare for possible pregnancy. A cycle is measured from the first day of your period to the day before your next period.

The average length of a menstrual cycle is 28 days, but everyone’s cycle is different. For example, teenagers might have cycles that last up to 45 days, whereas people in their 20s to 30s might have cycles that last 21 to 38 days.

The menstrual cycle has four phases.

Your period (menstruation)#

When you have a period, the lining of your uterus sheds and flows out through your vagina. Your period contains blood, mucus, and some cells from the lining of your uterus. The average length of a period is 3 to 7 days.

The follicular phase#

The follicular phase starts on the first day of your period and lasts for about 13 to 14 days. Changing hormone levels cause the lining of your uterus to thicken and follicles to grow on the surface of the ovaries. Usually only one follicle will mature into an egg.

Ovulation#

Ovulation is when a mature egg is released from an ovary. This usually happens once a month, about 2 weeks before your next period. You are most likely to get pregnant if you have unprotected sex around the time of ovulation.

The luteal phase#

After ovulation, the egg travels through the fallopian tubes towards your uterus, and the uterus lining continues to thicken in preparation for pregnancy.

If you become pregnant, you will not have a period. If you do not become pregnant, you will have a period and the menstrual cycle starts again.

When to see your doctor#

Talk to your doctor if you are worried about your periods – for example, if:

• Your period patterns change
• Your periods are getting heavier (you need to change your pad or tampon more often than every 2 hours)
• Your periods last more than 8 days
• Your periods come less than 21 days apart
• Your periods come more than 2 to 3 months apart
• You bleed between periods
• You bleed after sexual intercourse
• Your symptoms are so painful that they affect your quality of life

Key points#

• The menstrual cycle is a monthly series of changes that prepares your body for possible pregnancy.
• The average cycle is 28 days, but a normal cycle can range from about 21 to 38 days, and longer in teenagers.
• The four phases are menstruation, the follicular phase, ovulation, and the luteal phase.
• You are most likely to conceive around the time of ovulation, about 2 weeks before your next period.
• See your doctor if your periods change significantly, become very heavy or painful, or you bleed between periods or after sex.

Where to get help#