The menstrual cycle

What is the menstrual cycle?

The menstrual cycle is a natural but complex cycle of changes that your body goes through each month.

A menstrual 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 45 days, whereas people in their 20s to 30s might have cycles that last 21 to 38 days.

Phases of the menstrual cycle

The menstrual cycle has 4 phases.

1. Your period (menstruation)

When you have a period, your uterus lining sheds and flows out of 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.

2. The follicular phase

The follicular phase starts on the first day of your period and lasts for 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.

3. 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're most likely to get pregnant if you have unprotected sex around the time of ovulation.

4. The luteal phase

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

If you fall pregnant, you won't have a period. If you don't get pregnant, you'll have a period and the menstrual cycle will start 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 (i.e. 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
• your symptoms are so painful they affect your quality of life
• you bleed between periods
• you bleed after sexual intercourse.

More information

For more detailed information, related resources, articles and podcasts, visit Jean Hailes for Women’s Health.

Where to get help

• Your GP
• Gynaecologist
• Jean Hailes for Women’s Health