Menstrual cycle: normal

female reproductive system

The menstrual cycle is the name for the changes that happen in a woman’s body about once a month to prepare itself for a possible pregnancy. During each menstrual cycle, an egg is released from one of the ovaries and the uterus (womb) develops a lining in which a fertilised egg could implant. If the egg is not fertilised by sperm, as is the case in most cycles, the lining of the womb breaks down and leaves the body - this is commonly known as having a period.

Periods usually start in girls around the age of 12 years. Periods stop at menopause, which occurs, on average, around the age of 51 years in Australia.

The length of menstrual cycle is calculated by counting the first day of bleeding as day one and then counting until the last day before the next bleed (period). The length varies from woman to woman, from a short cycle of about 21 days to a long cycle of about 42 days. The average is commonly described as 28 days, although only about one in 10 women have a 28-day cycle.

In some women, menstrual cycles also vary slightly in length from month to month. Irregular cycles are most common during the year or so after starting your periods and the few years before menopause.

Menarche - getting your first period

Menarche is the name given to the time when a girl has her first period. The age at which this happens varies, but is usually between 9 and 14 years.

The average age of menarche has been gradually getting younger over a number of years. Why this is happening is not certain, but possible reasons for girls getting their periods at a younger age include increased rates of obesity, exposure to certain chemicals (which may be found in some foods and plastics) and stress (social or psychological).

Signs that your first period is on its way

Before their first period, most girls will have noticed signs of puberty, including the beginnings of breast development and hair growth in the pubic area and armpits. Girls may also start to notice a small amount of vaginal discharge - clear or white fluid or mucus that comes from the vagina. (This fluid helps keep your vagina clean and healthy.)

Periods usually start about 2 years after breasts first start to develop, and about one year after vaginal discharge starts happening.

It’s a good idea for girls who are aged around 10 or 11 to start bringing an emergency pad to school or to sleepovers, in case your period takes you by surprise. But don’t be embarrassed to ask for help if you get your period and you don’t have any supplies. Any trusted person, such as a teacher or parent will know how to help.

When to expect your next period

It’s uncommon for a regular menstrual cycle to follow your first period. Periods tend to occur in a haphazard way for the first year or so before settling into a more regular pattern, which is usually once every 24 to 30 days.

Once your periods start, it’s a good idea to track them by recording them in a diary, calendar or on a smartphone app. That way you can see if there is a pattern emerging and when to expect your next period.

Average length of periods

Periods tend to last for about 4 to 8 days. Most women bleed for about 5 days and lose about 35 to 80 mL of menstrual fluid (menstrual flow), which may be bright red, dark red or brown.

Starting periods earlier or later than average

Some girls get their first period when they are as young as 8 years old. If signs of puberty begin before about age 8 for girls, it is called precocious puberty. This may be normal for that girl, or it may be a sign of underlying hormonal problems. If your child starts puberty early you should see your GP or paediatrician.

Similarly, if a teenage girl has no signs of puberty by age 14 or has not started having periods by the age of 16, they should see a doctor to work out why.

You should also see your doctor if you stop having periods at any time or if your periods become irregular.

Personal care products to manage your periods

When it comes to managing your periods, there are several choices of personal care (sanitary) products. Most products can be purchased from supermarkets and pharmacies. You may want to use one or several of the options below.

Sanitary pads, or napkins, are are made of soft, absorbent material. They are shaped to fit inside your underwear and usually have an adhesive strip to stick the pad in place. They come in a variety of sizes to suit how heavy your flow is - heavy, medium or light.

You should change your pad every few hours. Used pads should be wrapped in toilet paper and put in the bin, never flushed down the toilet (which can block the plumbing).

Tampons are small cylinders of cotton (and sometimes synthetic material) that are designed to be gently inserted into the vagina to absorb the menstrual flow. Some tampons come with a special applicator designed to help you insert them.

Tampons come in different sizes - such as super, regular or slim/mini - that you choose according to how heavy your flow is. When inserted properly, you shouldn’t be able to feel the tampon inside you.

Tampons need to be changed at least every 4 hours hours or so. You remove them by gently pulling on the attached string. Used tampons should be disposed in the same way as pads - flushing them down the toilet can block the plumbing.

There is a small risk of toxic shock syndrome associated with tampon use. To reduce the risk, never leave tampons in for more than 8 hours and always wash your hands before inserting a tampon.

Menstrual cups are small, silicone or rubber devices that can be inserted into the vagina to collect your menstrual flow. They can be left in place for around 6-8 hours. When you remove a menstrual cup, you simply empty it into the toilet, wash the cup and you can then reinsert it.

These devices are reusable - they can last for several years before needing to be replaced, so are considered environmentally friendly. You can buy them from selected pharmacies and online.

Period underwear that has a built-in absorbent crotch area and reusable, environmentally-friendly cloth pads are also available, and can be purchased online. These environmentally-friendly products can be rinsed and washed according to instructions, then reused. There are a range of products with varying levels of absorbency.

Troublesome periods: what can be done?

Talk to your doctor or local Family Planning Clinic if you have heavy, painful or difficult to manage periods. Painful or heavy periods should always be investigated and treated - you should not have to put up with period pain or discomfort that affects your quality of life each month.

Phases of the menstrual cycle

The menstrual cycle is generally thought of in separate phases; the time frames provided are based on a 28-day cycle.

menstrual cycle

Menstruation (periods or menses)

The start of menstruation marks the first day of the menstrual cycle. Most women menstruate (bleed) for about 5 days.

During this phase, because fertilisation of an egg hasn’t happened, the lining of the uterus (called the endometrium) comes away from the uterus wall. The endometrium, together with some blood (from broken endometrial blood vessels) and mucus passes through the vagina to leave the body.

About 35 to 80 mL of menstrual fluid, or menstrual flow, is lost in a typical period. Menstrual flow can be bright red, dark red or brown, and it tends to get lighter after the first couple of days. It does not usually clot unless bleeding is very heavy.

The lining of the uterus will end up being about 1 mm thick at the end of a period.

The follicular phase

This phase is so-named because it is when several follicles develop in the ovaries. A hormone called follicle stimulating hormone (FSH) stimulates the growth of these follicles. About 3 to 30 follicles grow between days 8 and 10. Each follicle contains an egg, but by days 10 to 14 one follicle has overtaken the rest and has reached the correct stage of maturity.

This phase is also known as the proliferative phase because from days 6 to 14 the lining of the uterus is repaired and builds up to be thicker. This is stimulated by a hormone called oestrogen, which is secreted from the ovaries. The lining of the uterus will now be about 3 mm thick and has a velvety consistency.

The ovulatory phase

A surge of a hormone called luteinising hormone (LH) occurs just before day 14 in a 28-day cycle. This surge stimulates the mature follicle in one of the ovaries to release its egg (ovulation). The other follicles over-ripen and break down. Oestrogen and FSH levels also peak during this time.

Eggs are released from the right or left ovary at random. If one ovary is removed, the remaining ovary should release an egg every month. Some women can feel a pain on one side of the abdomen around the time the egg is released. This is known as ‘mittelschmerz’ — a German word translating as ‘middle pain’.

Once an egg is released, it takes about 5 days to travel down the fallopian tube to the uterus.

The luteal or secretory phase

This phase follows ovulation and lasts from day 15 to day 28.

After a follicle ruptures to release its egg, it closes and forms a what is called a corpus luteum. The corpus luteum secretes progesterone and a small amount of oestrogen. Progesterone causes your body temperature to rise slightly until the start of the next period (see diagram). This rise in temperature can be plotted on a graph and gives an indication of when ovulation occurred.

Progesterone also acts on glands in the endometrium (lining of the uterus) causing it to thicken and secrete fluid. The thickened, secretory endometrium is made in preparation in case an egg is fertilised - the endometrium can feed an implanted embryo until a placenta has formed.

When an egg is not fertilised, the corpus luteum starts to break down after about 14 days. This is when progesterone production rapidly drops and the oestrogen level decreases. The reduced levels of these hormones causes the blood vessels in the endometrium to go into spasm, cutting off the blood supply to the top layers of the endometrium.

Without oxygen and nutrients from the blood, the endometrial cells begin to die. The tissue breaks down and there is bleeding from the damaged blood vessels. This is how the new menstrual cycle begins.

Last Reviewed: 9 May 2018


1. Family Planning NSW. Menstrual cycle and period problems (updated Nov 2012). (accessed Apr 2018).
2. Jean Hailes. About the menstrual cycle (updated 9 Dec 2013). (accessed Apr 2018).
3. Merck Manual Consumer Version. Menstrual cycle. (accessed Apr 2018).
4. American College of Obstetricians and Gynecologists (ACOG). Your first period (frequently asked questions especially for teens) (May 2015). (accessed Apr 2018).
5. Mayo Clinic. Preparing your child for menstruation (updated 24 Aug 2017). (accessed Apr 2018).
6. Mayo Clinic. Precocious puberty (updated 17 Nov 2017). (accessed Apr 2018).


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