SummaryRead the full fact sheet
- The menstrual cycle is complex and controlled by many different glands and the hormones that these glands produce.
- The four phases of the menstrual cycle are menstruation, the follicular phase, ovulation and the luteal phase.
- Common menstrual problems include heavy or painful periods and premenstrual syndrome (PMS).
- Knowing when in the menstrual cycle a woman is most likely to conceive can increase the chance of pregnancy.
The menstrual cycle is a natural process. It is a complex cycle controlled by female hormones that cause regular bleeding (periods). The menstrual cycle has four phases: menstruation, the follicular phase, ovulation and the luteal phase.
What is the menstrual cycle?
The menstrual cycle prepares your body for pregnancy. If you are not pregnant, your hormones send a signal to your uterus to shed its lining. This becomes your period. Once you start your period, the cycle starts again.
A menstrual cycle is measured from the first day of your period to the first day of your next period. The average length of a menstrual cycle is 28 to 29 days, but every woman’s cycle is different. For example, teenagers might have cycles that last 45 days, whereas women in their 20s to 30s might have cycles that last 21 to 38 days.
Your first period is called menarche. In Western countries, the average age for a first period is 12 to 13, but it can start as early as nine and as late as 16.
Phases of the menstrual cycle
There are four main phases of the menstrual cycle.
Menstruation is commonly known as a period. When you menstruate, your uterus lining sheds and flows out of your vagina. Your period contains , mucus and some cells from the lining of your uterus. The average length of a period is three to seven days.
Sanitary pads, tampons, period underwear or menstrual cups can be used to absorb your period. Pads and tampons need to be changed regularly (preferably every three to four hours) and menstrual cups should be changed every eight to 12 hours.
2. The follicular phase
The follicular phase starts on the first day of your period and lasts for 13 to 14 days, ending in ovulation. The pituitary gland in the brain releases a hormone to stimulate the production of follicles on the surface of an ovary. Usually, only one follicle will mature into an egg. This can happen from day 10 of your cycle. During this phase, your uterus lining also thickens in preparation for pregnancy.
Ovulation is when a mature egg is released from an ovary and moves along a fallopian tube towards your uterus. This usually happens once each month, about two weeks before your next period. Ovulation can last from 16 to 32 hours.
It is possible to get pregnant in the five days before ovulation and on the day of ovulation, but it’s more likely in the three days leading up to and including ovulation. Once the egg is released, it will survive up to 24 hours. If sperm reaches the egg during this time, you may get pregnant.
4. The luteal phase
After ovulation, cells in the ovary (the corpus luteum), release progesterone and a small amount of oestrogen. This causes the lining of the uterus to thicken in preparation for pregnancy.
If a fertilised egg implants in the lining of the uterus, the corpus luteum continues to produce progesterone, which maintains the thickened lining of the uterus.
If pregnancy does not occur, the corpus luteum dies, progesterone levels drop, the uterus lining sheds and the period begins again.
Common menstrual problems
Some of the more common menstrual problems include:
- – hormonal events before a period can trigger a range of side effects in women at risk, including fluid retention, headaches, fatigue and irritability. Treatment options include exercise and dietary changes
- – or painful periods. It is thought that the uterus is prompted by certain hormones to squeeze harder than necessary to dislodge its lining. Treatment options include pain-relieving medication and the oral contraceptive pill
- (previously known as menorrhagia) – if left untreated, this can cause . Treatment options include oral and a to regulate the flow
- – or absence of menstrual periods. This is considered abnormal, except during pre-, , and . Possible causes include low or high body weight and excessive exercise.
When to see your doctor
Talk to your doctor if you are worried about your period.
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 two hours)
- your periods last more than eight days
- your periods come less than 21 days apart
- your periods come more than two to three months apart
- your symptoms are so painful they affect your daily activities
- you bleed between periods
- you bleed after sexual intercourse.