Key points about menstruation

  • Menstruation (menstrual period, period or menses) is normal vaginal bleeding occurring for about 5 days every month as part of the monthly menstrual cycle.
  • Periods usually start between the ages of 10 and 16 as girls go through puberty and continue until menopause.
  • Every month, if no pregnancy occurs, your uterus (womb) sheds its lining.
  • The menstrual blood is partly blood and partly tissue from inside your uterus. It passes out of your body through your vagina.
  • As well as vaginal bleeding, you may experience discomfort, pain and changes in mood around the time of your period.
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Multiple hormones are involved in the menstrual cycle and everybody is a bit different. The range of ‘normal’ for periods is wide, but there are some common features.

Starting age (menarche)

  • Periods generally start between 10 and 16 years of age, about 2 years after breasts first start to develop.
  • Girls often start their periods at a similar age to other women in their family – if you can, find out when your mother, sister or grandmother started.

Cycle pattern

  • Periods are often not regular when they first start, but generally settle into a regular pattern after about 3 years.
  • Some women never have a regular cycle.
  • Periods occur anything from every 21 to every 40 days.
  • The commonly quoted cycle of 28 days occurs in just 1 woman in 10.
  • The first day of bleeding is counted as day 1 for a woman's cycle.
  • If you have a 4-week cycle, you ovulate (release an egg) around day 14 and have a period 14 days later (if a pregnancy has not occurred).
  • If your cycle is 35 days long, then you are likely to ovulate around day 21.
  • Contraception is needed throughout your cycle, as the timing of ovulation can be unpredictable – this means you can become pregnant at unexpected times.

Image showing hormone fluctuations during a menstrual cycle



Image credit: 123rf

Blood loss

  • About 30 to 40 ml of blood is lost per period, but it can look like more.
  • To help work out how much blood is lost, a tampon holds around 5 ml of blood, while sanitary pads hold anything from 5–15 ml each.
  • Bleeding can last anywhere from 3 to 7 days (5 days being the average).
  • Bleeding is generally heaviest for the first day or two, then lighter over the next day or two and maybe finishing with a day or so of spotting (very light bleeding).

Tissue loss

The blood does not usually clot, but small amounts of tissue from the lining of your uterus (which are normal) can look a little bit like clots. The difference is that clots are dark in colour and are generally accompanied by heavy bleeding, while uterine tissue is lighter coloured. Another way to tell the difference is if you squeeze them in between bits of toilet paper, clots will break up and bits of tissue won’t.

Level of discomfort

Some discomfort is normal, but periods are not generally painful for most women. 

As well as vaginal bleeding, you may also have one or more of the following:

  • abdominal or pelvic cramping
  • bloating and sore breasts
  • lower back pain
  • food cravings
  • mood swings and irritability
  • headache and fatigue.

Approaching menopause

  • As you approach menopause, your periods may become more irregular again.
  • Periods tend to finish between the ages of 40 and 55.

Read more about menopause.

Bleeding between periods

Bleeding between periods or after sexual intercourse is not a normal part of having periods, so see a doctor if you experience this.

No periods

Only under the following circumstances is it normal not to have periods:

  • before you reach puberty
  • when you are pregnant
  • if you are breastfeeding (however, breastfeeding doesn't necessarily prevent pregnancy)
  • if you have reached menopause
  • take the combined oral contraceptive hormone pills every day (missing the 7 non-hormonal pills in the packet).

If you have no periods, but you should, it is known as amenorrhoea. There are 2 categories of amenorrhoea:

  • primary amenorrhoea – your periods never started and you are 15 years or older.
  • secondary amenorrhoea – you started having periods, but they stopped for 6 months or more.

Amenorrhoea may be caused by:

  • strenuous exercise
  • stress
  • some medications, including the oral contraceptive pill (it can take 3–6 months to start having normal periods again after stopping the pill)
  • chronic illness
  • problems with your ovaries
  • hormonal imbalances such as polycystic ovarian syndrome, issues with the functioning of your thyroid gland, hypothalamus (the part of your brain that helps regulate your menstrual cycle) or pituitary gland
  • anatomical problems with your uterus, cervix or vagina
  • the absence of puberty
  • depression and some other forms of mental illness
  • low body weight.

If your lack of periods is due to not ovulating (releasing an egg), you may find it difficult to get pregnant. You may also be at risk of osteoporosis (weak bones). 

See your doctor if you are not having periods (except for the reasons listed above as normal). There are different treatment options available, depending on the cause of your amenorrhea. 

Heavy periods

Menorrhagia is the term given to periods that are long and heavy. It affects around 20–25% of women. Menorrhagia may involve periods that are prolonged (lasting for longer than 7 days), and/or excessive bleeding with flooding or clots.

  • Women with menorrhagia may lose 80 ml or more of blood per period, compared with the 30–40 ml lost by most women.
  • If you are changing your tampon or sanitary pad more often than every hour, flooding (soaking through your pads/clothing) or becoming anaemic, this is a good indication you have menorrhagia.

It is one of the main reasons for having a hysterectomy (removing the uterus with surgery), although there are other less extreme treatments to try first such as a Mirena (a type of intrauterine device also used for contraception). Read more about heavy periods.

Painful periods

Some women have painful periods. Dysmenorrhoea is the term given to periods that are more painful than expected ‘normal’ discomfort. This may just be a symptom of your period or a sign of an underlying condition, such as endometriosis. Read about painful periods.

There are a range of options for absorbing the blood flow of your period. 

  • Pads are cotton pads that stick to your underwear to soak up blood, and which you throw away after use. They come in many different shapes and amount of blood they can soak up.
  • Tampons are pieces of cotton with a string at one end. You put them into your vagina to soak up your blood, and pull them out using the string. You should change a tampon every 4–6 hours or as needed. You can choose from a range of sizes, depending on how heavy your period is. 
  • Menstrual cups are soft rubber cups that are put into your vagina to catch the blood flow. You empty the cup every 8–12 hours, rinse it under water, and put it back in.
  • Reusable pads are cloth pads that you can wash and reuse. They are usually made of absorbent material like cotton or bamboo. It is recommended that after using the pad, you rinse it, soak it overnight and then wash it.  
  • Period underwear looks and feels like your regular underwear, but are very absorbent. They can be used instead of pads or tampons when you have a light flow, or as a back-up when you have a heavy flow.  

Women track their periods for a variety of reasons, including being prepared and knowing when to expect your period, understand your body's reactions to different phases of your cycle, planning a pregnancy and having informed conversations with healthcare providers (doctors often ask when your last period was). 

Keeping track of your periods can be done by simply remembering (which isn't always easy), keeping a paper diary and marking the calendar, or with the use of period tracking smart phone apps. Read about period tracking apps.

Periods(external link) Sexual Wellbeing Aotearoa, NZ
Managing your period(external link) Sexual Wellbeing Aotearoa, NZ

How to guides(external link) The Period Blog
How not to be afraid the first time you use a tampon(external link) WikiHow


Patient information for heavy periods and bleeding in between periods(external link) Auckland DHB, NZ, 2014
Answers to all those interesting questions about growing up(external link) Sexual Wellbeing Aotearoa, NZ


  1. Heavy menstrual bleeding(external link) Royal Australian and New Zealand College of Obstetricians and Gynaecologists
  2. Heavy menstrual bleeding clinical care standard(external link) Australian Commission on Safety and Quality in Health Care, 2017
  3. Physiology of the normal menstrual cycle(external link) UpToDate, 2019
  4. Clinical manifestations and diagnosis of menopause(external link) UpToDate, 2020
  5. The pill(external link) Sexual Wellbeing Aotearoa, NZ
  6. Late and irregular periods(external link) Sexual Wellbeing Aotearoa, NZ

Clinical resources

Reproductive hormones – the right test, at the right time, for the right patient(external link)(external link) BPAC, NZ, 2013
Menstruation(external link)(external link) Starship Clinical Guidelines, NZ, 2011
Heavy menstrual bleeding(external link)(external link) Royal Australian and New Zealand College of Obstetricians and Gynaecologists
Heavy menstrual bleeding clinical care standard(external link)(external link) Australian Commission on Safety and Quality in Health Care, 2017
Physiology of the normal menstrual cycle(external link)(external link) UpToDate, 2019
Clinical manifestations and diagnosis of menopause(external link)(external link) UpToDate, 2020

Continuing professional development 

1. Video: PHARMAC seminar: Women's health 2019, 1a of 6, amenorrhea Amenorrhea – pointers to quick evaluation in primary care (parts 1 and 2) – Stella Milsom (25 minutes + 17 minutes = 42 minutes)

This video may take a few moments to load.

(Pharmac seminars, NZ, 2019)

Video: PHARMAC seminar: Women's health 2019, 1b of 6, amenorrhea

This video may take a few moments to load.

(Pharmac seminars, NZ, 2019)

2. Video: PHARMAC seminar: Women's health 2019, 2 of 6, hypothalamic amenorrhea Hypothalamic amenorrhea – Megan Ogilvie (32 minutes)

This video may take a few moments to load.

(PHARMAC seminars, NZ, 2019)


All about growing up
Sexual Wellbeing Aotearoa, NZ, 2010

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Credits: Healthify editorial team. Healthify is brought to you by Health Navigator Charitable Trust.

Reviewed by: Dr Phoebe Hunt, Auckland DHB

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