About the menstrual cycle

Learn all about the menstrual cycle, what happens, how long a menstrual cycle usually is and when you should seek help.

The video below is a fantastic resource for girls and women of all ages and cultures, covering the changes that come with puberty and giving educational insight into why the period occurs and what they can expect when it does.

What is a menstrual cycle?

female reproductive systemThe menstrual cycle is a cycle of body changes controlled by female hormones that cause a regular bleed. This bleed, which usually occurs monthly, comes from the uterus (womb) and flows out from the vagina. 'Period', 'menstruation' or 'menses' are all words used to describe the blood loss women experience at this time.

The menstrual cycle begins at menarche (the first period) and ends with menopause (the final period).  Every woman's cycle is unique and individual. The average age of menarche in Western countries is 12-13 years, but it can start as early as nine and as late as 16. If your periods have not started by 16-17, you should see your doctor to investigate why they haven't started. Most women reach menopause between 45-55 years and the average age of menopause for women from a western country is 51-52 years.

Why do you have a menstrual cycle?

The role of the menstrual cycle is to prepare the body for pregnancy. When a pregnancy does not occur, a period results. On average, a woman in Australia will have 450-500 periods in her lifetime.

How does the menstrual cycle occur?

The menstrual cycle occurs because of a complex relationship between hormones from the brain and ovaries, which leads to the development and release of an egg from the ovary (ovulation) and growth of the internal lining (endometrium) of the uterus, to prepare it for pregnancy. When the hormones signal the uterus that there is no pregnancy, the lining starts to break down and separate from the wall of the uterus and the period begins. Once the lining has separated from the wall of the uterus, the cycle starts again.

How long is a normal menstrual cycle?

Menstrual cycles vary between women and are measured from the first day of the period to the first day of the next period. In adolescents a cycle may be as long as 45 days, however by the 20s-30s a cycle is usually between 21-38 days.

For a 28 day cycle:

Day 1 Day 2 Day 3 Day 4 Day 5 Day 6 Day 7
Day 8 Day 9 Day 10 Day 11 Day 12 Day 13 Day 14
Day 15 Day 16 Day 17 Day 18 Day 19 Day 20 Day 21
Day 22 Day 23 Day 24 Day 25 Day 26 Day 27 Day 28

Periods change over a woman's lifetime.  Sometimes they change after pregnancy and in some women they get heavier in perimenopause (perimenopause is the transition time from regular periods to the final period and menopause) and lighter and shorter closer to the final period or menopause.

What to expect during your period?

The bleeding can vary in quality and quantity, from a small amount to a heavy loss, and can vary in colour from black/brown to bright red. The period may last from four to eight days, and most women lose less than 80ml of blood (about 1/3 of a cup) in total.

The flow changes over the course of your period and can be heavier for the first three days and then lighter in the next few days. The blood colour will reflect this change in flow rate and may change from dark or bright red initially, to dark brown later in the cycle. The period contains blood, mucous and some cells from the lining of the uterus. Some small clots may be normal, but if the clots become frequent or larger, see your doctor.

In some women, at the time of ovulation (release of an egg from the ovary), which usually occurs about two weeks before the next period, there may be some slight spotting and/or pain. This is because of a normal change in some of the hormones following ovulation. If pain or bleeding at the time of ovulation frequently last longer than three days, you may need to see your doctor, especially if you know you are at higher risk of endometrial (uterine) cancer.

Odour (smell)

Most women have some odour related to bleeding, but little is known about why it is sometimes stronger. If the odour is so strong it worries you, then discuss your concerns with your doctor.

Bowel habits

The body makes substances called prostaglandins (natural body chemical), especially just before, and in the first few days of, the period. These prostaglandins cause muscle contractions in internal organs and in combination with the hormonal pattern in the premenstrual week can cause changes in bowel habits. Some women notice difficulty in opening their bowels just prior to their period as if they are constipated, and then when the period starts the bowel motions becomes loose.

Signs or symptoms before your period

Premenstrual symptoms may occur in the one to two weeks before your period. Symptoms may include irritability, bloating, pimples and tiredness. Normally these symptoms might be irritating but would not interfere with your day to day activities.  More commonly, around two–thirds of women experience some breast pain during their cycle.  Symptoms appear to peak in adolescence and again in perimenopause, possibly because of fluctuating hormone levels. 

If you are having regular periods but have spotting of blood for a week or so before each period there can be several reasons for this so see your doctor.

Period symptoms usually settle when the period starts or in the first two to three days of the period. Period pain that interferes with your everyday life is not normal. 15-20% of women have symptoms so severe their lifestyle is affected and they cannot function properly. If this occurs, you should seek help from your doctor.

Sanitary products


Pads, sanitary pads or napkins are made of absorbent material and come in a range of thicknesses and shapes. Pads may need to be changed three to four hourly on the heaviest day. If you find that using pads causes irritation, you may need to use pads that are made from 100 per cent cotton and are scent free. Reusable, environmentally friendly pads are available.


Tampons are absorbent 'plugs' made of cotton, or a combination of cotton and a synthetic material. Tampons are inserted into the vagina and are available in various sizes. They can be used by all ages and should be changed every three to four hours.

Very rarely, toxic shock syndrome can occur when using tampons. This is due to a rapid growth of normal bacteria releasing a toxin, which leads to symptoms of 'shock' such as feeling unwell, fever, rash, diarrhoea and headache. Never keep a tampon inserted in your vagina for more than eight hours and always wash your hands before inserting.

Menstrual cup

The menstrual cup has been available for many years and is long-lasting (up to 5-10 years) but is used by a very small number of women. The menstrual cup (made out of either rubber (latex), silicone or thermoplastic rubbers) sits in the vagina over the cervix and collects the menstrual flow. It should be washed at least every 12 hours using fresh or soapy water only. Menstrual cups are considered environmentally friendly as they are reusable. They are a number of menstrual cups available including Lunette and Femmecup.

When to see your doctor

There are many reasons you may need to see your doctor about your periods including:

  • changes in the pattern of your period
  • increasingly heavy periods
  • long periods of more than 8 days
  • periods that come less than 3 weeks apart
  • periods coming more than 2-3 months apart
  • painful periods causing you to stay home
  • bleeding between periods
  • bleeding after intercourse

Your menstrual cycle is a normal process for your body. Each woman experiences her menstrual cycle differently, most without any difficulties. If there is any change in the cycle that worries you, see your doctor.

Last updated 24 July 2017 — Last reviewed 09 December 2013

** Currently under review **

This web page is designed to be informative and educational. It is not intended to provide specific medical advice or replace advice from your health practitioner. The information above is based on current medical knowledge, evidence and practice as at December 2013.

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