It is important for a woman to understand how the menstrual cycle or period happens, what is normal bleeding, when is the fertile time and when she should see a doctor about her period.

What is the menstrual cycle?

The menstrual cycle is the series of changes which occur in the female body (usually each month) to prepare the body for pregnancy. The menstrual cycle is controlled by the rise and fall of several of the body’s hormones or chemical messengers that control certain body functions. If a woman does not become pregnant during the cycle, she will have a period. A cycle is counted from the first day of one period to the first day of the next period. Most women will have 450-500 periods in their life.

What is menstruation?

Menstruation is a woman’s monthly bleeding often called a period. When a woman menstruates, the body is shedding the lining of the uterus (womb or bag that holds the baby during pregnancy). This blood flows out of the opening (called the cervix) of the uterus, and then out of the body through the vagina.

What can girls & women expect during a period?

The bleeding of a period can vary from very light to very heavy, and it can vary in colour from black/brown to bright red. Most women lose less than 80ml of blood (about four tablespoons in total) even though it often seems like more. The period contains blood, mucous and some cells from the lining of the uterus. Some small clots may be normal.

The period usually lasts from four to eight days. The flow of blood will change during the period; it is usually heavier for the first few days and then becomes lighter.

Many women will have some crampy discomfort/pain early in the period and for some women the pain can be quite significant, heat packs and simple pain relief medication may help. Some women may find that the oral contraceptive pill, depo-provera, Implanon or Mirena intra-uterine contraceptive device may also help if they have heavy or painful periods. If pain is severe it is a good idea to see a doctor.

Some women may also have some slight spotting and/or pain, when they ovulate (release of an egg). This is usually about two weeks before the next period.

What are the signs & symptoms a period is on the way?

Pre-menstrual (before the period) symptoms can happen in the one to two weeks before a period. Symptoms may include:

  • feeling grumpy or bad tempered
  • bloating
  • sore breasts
  • pimples
  • tiredness.

Normally these symptoms might be annoying but would not interfere with day to day activities. They usually settle when the period starts or in the first two to three days of the period.

In some women, symptoms can be so severe that their daily routine is affected and they cannot function properly. If this happens women should see their doctor or women’s health nurse.

When do periods start & finish?

The time when the menstrual cycle begins is called menarche (the first period). This usually happens when girls are about 12-13 years old, but can start as early as nine and as late as sixteen.

In the first two or three years after a girl’s period has started, the cycles can be irregular because ovulation does not always happen with each cycle. It takes the body a few years to develop a routine of releasing an egg and shedding the lining of the uterus every month.

The menstrual cycle ends with menopause (the final period). A woman has reached menopause when it is twelve months since her last cycle. The average age of menopause is 51 years but it may happen from 45-55 years. When a woman’s body is getting near the end of its reproductive life, the periods are often irregular like they were when they first started. This ‘winding down’ time before menopause is called perimenopause.

What is the normal length of the menstrual cycle?

The length of the menstrual cycle is measured from the first day of one period to the first day of the next period. The length of the cycle can vary, for example in teenagers a cycle might be as long as 45 days, however by the 20-30s a cycle is usually between 21-38 days.

How does the menstrual cycle occur?


This video clip outlines the menstrual cycle, it is an animated version of what is written below.

Figure 1 shows a typical 28 day menstrual cycle from one period to the next. If the cycle is shorter or longer then ovulation may happen sooner or later.

Figure 1: The menstrual cycle

Day 1-6

If a woman is not pregnant the period begins this is Day 1 of the menstrual cycle.
At the same time, the brain releases a hormone which causes the ovary to produce little sacs of fluids (follicles) on its surface; each follicle contains an immature egg.
Blood flows out of the cervix of the uterus, and then out of the body through the vagina usually for the next 3-7 days.

Day 7-14

Bleeding has usually  stopped by now
Of all the follicles which started to grow, only one continues to grow with an egg that develops further
The lining of the womb or uterus starts to thicken and gets ready in case a fertilised egg is implanted there.

Day 14

Hormones cause the now fully grown egg to burst out of the follicle and leave the ovary. This is called ovulation.

Day 15-20

The egg travels down the tube towards the uterus
This is the time of the cycle when pregnancy can occur. If the egg meets one of many sperm produced by a man, the egg may be fertilised. A fertilised egg will then move down the tube and attach to the wall of the uterus where it will continue to grow.

Day 21-28

If the egg is fertilised a period will not occur and different hormones help the pregnancy to continue
If the egg is not fertilised the hormone levels will start to go down, this causes the lining of the uterus to break down and separate from the wall and then the period begins


What to use during a period

There are a variety of products available to use during a period including pads and tampons:

Pads: also known as sanitary pads or napkins. These are made of absorbent material and come in different thicknesses and shapes. If using pads causes irritation, women may need to use pads that are made from 100% cotton and have no perfume. Pads usually need to be changed every 3-4 hours. Most pads are disposable but there are reusable/washable pads also available.

Tampons: are absorbent ‘plugs’ made of cotton, or a combination of cotton and a synthetic material and are available in different sizes. They can be used by all ages. Hands should be washed before a tampon is inserted into the vagina.

Tampons should be changed every three to four hours: it is important not to leave a tampon in for too long (never more than 8 hours). There is a condition called Toxic Shock Syndrome which can happen when bacteria (germs) multiply very fast in the vagina releasing a toxin (poison) which can cause women to become sick with symptoms such as feeling unwell, fever, rash, diarrhoea and headache.

Is it ok to have sex during a period?

There is no medical reason why women can’t have sex during their period. Some women prefer not to because of personal, cultural or religious preferences. It is important to practise safe sex at any time to prevent contracting sexually transmissible infections such as Chlamydia, HIV or Hepatitis B.

Is it possible to get pregnant during a period?

It is possible to become pregnant during a period. Even though ovulation usually happens from day 7-10 of the menstrual cycle (about two weeks before a period), it is possible for a woman to be fertile late in her cycle, up until the day the period begins or early in her cycle while she still has her period. It is also possible for sperm to stay alive inside the woman’s tubes for up to a week. So if a woman does not want to become pregnant, it is important that she uses a reliable form of contraception.

When to see a doctor about the menstrual cycle?

A period can be different from woman to woman, some women have very heavy periods others have a very light flow and both can be quite normal.

Sometimes though, bleeding is not normal and may be too heavy and cause a woman to feel very tired or dizzy or cause the iron levels in the blood to get too low.

It is important for a woman to see a doctor about the menstrual cycle if she is:

  • changing a pad or tampon every hour
  • changing a pad overnight
  • clots bigger than a 50 cent piece in size
  • bleeding for more than seven days
  • bleeding for more days than usual
  • bleeding excessively
  • bleeding between periods
  • having period pain that interferes with daily life

A woman should also see a doctor if

  • she is not having periods by the age of 16
  • or if she normally has regular periods but then doesn’t have a period for more than 3 months and is not pregnant.  This may be part of a normal transition towards menopause in older women (40+ years) and it is normal for women using Implanon, Depo-provera or the Mirena IUCD to stop having periods. 

Last updated 18 April 2016 — Last reviewed 15 August 2013

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 August 2013.

Subscribe To our newsletters