About the menstrual cycle


Learn all about the menstrual cycle, what happens during a cycle, 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?

The menstrual cycle is a cycle of bodily 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.

female reproductive system, pelvic, uterus

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 perio-ds have not started by 16-17, you should see your doctor to investigate why they haven't started. Most women reach menopause between 45 and 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. This 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 to the uterus that there is no pregnancy, the lining starts to break down and separate from the wall of the uterus, beginning the period. 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 might be as long as 45 days; however, by the time a woman reaches her 20s-30s, a cycle is usually between 21 and 38 days.

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

What to expect during your period?

The bleeding during a period can vary from one cycle to another 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 can last from four to eight days, and most women lose less than 80ml of blood (about one-third 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 can 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 might be some slight spotting and/or pain. This is because of a normal change in some of the hormones with ovulation. If pain or bleeding at the time of ovulation frequently lasts longer than three days, you need to see your doctor.

The below table shows when a woman with a 28-day cycle would most likely ovulate.

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

Odour (smell)

Most women have some odour related to bleeding, but little is known about why it is sometimes stronger. It might be related to the length of time you leave your sanitary pad on or tampon in. If the odour is so strong it worries you, discuss your concerns with your doctor.

Bowel habits

The body makes substances called prostaglandins (a natural body chemical), especially just before, and during 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 become loose and more frequent.

Signs or symptoms before your period

Premenstrual symptoms may occur in the one to two weeks before your period. Symptoms can include irritability, mood changes, bloating, pimples and tiredness. Normally these symptoms might be irritating, but would not interfere with your day-to-day activities. More commonly, around two out of three 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, see your doctor, as there can be several reasons for this.

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

Sanitary products

Pads

Pads, sanitary pads or napkins are made of absorbent material and come in a range of thicknesses and shapes. Pads might need to be changed every three to four hours on the heaviest day. If you find that using pads irritates your vulva, you may need to use pads that are made from 100% cotton and are scent-free. Reusable, environmentally friendly pads are available.

Tampons

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 one.

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. Made from either rubber (latex), silicone or thermoplastic rubbers, the menstrual cup sits in the vagina over the cervix and collects the menstrual flow. It should be washed at least every 12 hours using only fresh or soapy water. Menstrual cups are considered environmentally friendly as they are reusable. There are several menstrual cups available, including Lunette and Femmecup.

When to see your doctor

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

  • changes in the pattern of your periods
  • increasingly heavy periods
  • long periods of more than eight days
  • periods that come fewer than three weeks apart
  • periods coming more than two to three months apart
  • painful periods that cause 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 your cycle that worries you, see your doctor.

References

  1. Mihm M, Gangooly S, Muttukrishna S. The normal menstrual cycle. Anim Reprod Sci. 2011;124:229–36.

  2. Speroff L, Glass R, Kase N. Regulation of the menstrual cycle. In: Clinical gynecologic endocrinology and infertility. 7th edn. Philadelphia: Lippincott, Williams and Wilkins, 2005.

Last updated 26 September 2018 — Last reviewed 10 July 2018

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 July 2018.

Subscribe To our newsletters