Page last reviewed: 13/07/2011

A period is when blood leaves the womb through the vagina. This happens about every 28 days. Girls most commonly start their periods around the age of 12.

It is normal for a female to not have any periods under the following circumstances:

  • When a girl has not yet gone through puberty.
  • When a woman is pregnant, breastfeeding or going through the menopause (usually at the age of 40 or older).
  • When a woman has had a hysterectomy (operation to remove the womb).

However, an absence of periods when they should normally occur, known as amenorrhoea, may indicate an underlying health problem or severe weight loss (see Causes). When there is amenorrhoea, ovulation (the release of eggs) does not occur.

Amenorrhoea may be categorised as either primary or secondary.

Primary amenorrhoea

Primary amenorrhoea is the failure to start your periods. It is regarded as abnormal if:

  • you have not started sexual physical development and periods by the age of 14, or
  • you have not started your periods by the age of 16 but have normal sexual physical characteristics for your age (see Diagnosis)

Primary amenorrhoea affects only about three girls in every 1,000.

Secondary amenorrhoea

Secondary amenorrhoea is defined as the absence of periods for six consecutive months in a woman who previously had regular periods.

Secondary amenorrhoea suggests that there is a gynaecological disorder or a more general cause, such as being severely underweight. It affects about three females in every 100.

Up to 50% of competitive long-distance runners (those who run 80 miles or more a week) and up to 44% of professional ballet dancers have amenorrhoea (see Causes).


There is usually an underlying cause for amenorrhoea that can be treated. Treating it often brings back your periods.

Irregular or infrequent periods

An associated condition, known as oligomenorrhoea, refers to infrequent periods. These periods usually occur every three to six months, and may be irregular.

Page last reviewed: 13/07/2011

There are many possible causes of absent periods, which include:

  • A temporary delay in periods starting, which may be a family tendency.
  • Being severely underweight as a result of an eating disorder or illness. Regular periods are unlikely if the body mass index (weight in kg divided by the height in metres squared) is less than 19 (the normal range is 20-25).
  • Doing excessive amounts of exercise. Absent periods are particularly common in athletes who compete in endurance events.
  • Severe stress, depression or other emotional disturbance.
  • A problem with the level of hormones that control ovulation and menstruation.
  • Various medications and drugs, including antipsychotics, previous chemotherapy or radiotherapy, and cocaine.
  • Polycystic ovary syndrome, a condition associated with multiple cysts in the ovaries, which can cause absent or disturbed periods, along with other symptoms 
  • Severe long-term illness, or an under- or overactive thyroid gland
  • Premature ovarian failure, a disorder of the ovary.
  • The absence at birth of the vagina or womb, or a hymen that completely closes off the vagina (these are rare).

There are very rare cases of amenorrhoea where the true gender of a child is confused because of poorly developed genital organs at birth.

Page last reviewed: 13/07/2011

See your GP if:

  • you are 14 or older, have not started your periods and have not started sexual physical development (see box)
  • you are 16 or older and have not started your periods, but have normal physical features of puberty, or
  • you used to have periods but have not had one for the last six consecutive months (secondary amenorrhoea)

GP investigations

Your GP will determine whether you have primary amenorrhoea (a failure to start your periods) or secondary amenorrhoea. They will then try to identify the cause of your absent periods.

First, you may be offered a pregnancy test to rule out pregnancy.

Your GP will also take full details, including noting your medical history, work and activity, family medical history, sexual history, and any emotional upsets or changes in body weight. They will also assess whether you are going through the normal physical stages of puberty (see box).

  • If your GP diagnoses primary amenorrhoea, you may be referred to a gynaecologist (women's health specialist). See below.
  • If your GP diagnoses secondary amenorrhoea, they can usually identify the underlying cause and treat it. In some cases, they may refer you to a gynaecologist or endocrinologist (hormone disorder specialist). See below.

Referral: primary amenorrhoea

Your GP may diagnose primary amenorrhoea and refer you to a gynaecologist if:

  • you have not started your periods by the age of 14, and your body shows no signs of going through puberty (see box), or
  • you have normal features of puberty but have not started your periods by the age of 16

Your specialist may give you a full gynaecological examination and carry out various tests, which include:

  • blood tests to determine your levels of prolactin, thyroid-stimulating hormone, follicle-stimulating hormone and luteinising hormone (abnormal amounts of these may be causing your amenorrhoea)
  • a pelvic ultrasonography, computerised tomography (CT) scan or MRI scan. These scans take detailed pictures of the inside of your body and reveal any problems with your vagina or womb.

Referral: secondary amenorrhoea

Your GP may diagnose secondary amenorrhoea and refer you to a gynaecologist or endocrinologist if:

  • the cause cannot be identified
  • the cause needs to be confirmed, or
  • specialist treatment is needed, for example, for infertility

Possible causes that need confirmation are:

  • premature ovarian failure (a disorder of the ovary)
  • Polycystic ovary syndrome (PCOS)
  • infertility
  • hyperprolactinaemia (high levels of a hormone called prolactin in the blood)
  • an increased level of blood testosterone that is not caused by PCOS

You may be referred to a psychiatrist or psychologist if your GP thinks that you have an eating disorder. You may be referred to a dietitian if you are underweight (body mass index less than 19).

Assessing your sexual development

Your doctor will assess your development through puberty by using the following guide:

  • Stage 1: breasts have started to develop and pubic hair has started to grow.
  • Stage 2: breast buds have formed and there are long, downy pubic hairs around the genitals.
  • Stage 3: breast buds are larger and pubic hair is growing.
  • Stage 4: breasts are in a 'mound' form and pubic hair is in the triangular shape, but not fully grown.
  • Stage 5: breasts are fully formed and pubic hair is adult in shape, quantity and type, and spread to the inner thighs.

Page last reviewed: 13/07/2011

Treating the underlying cause of your absent periods may bring them back. For example:

  • If absent periods are associated with overexercising, modifying the exercise programme and improving your diet and weight may bring your periods back. If absent periods are caused by dramatic weight loss, a programme of weight gain will be recommended. You may be referred to a psychiatrist if you have an eating disorder
  • If absent periods are associated with stress, you may be referred for counselling or psychological therapy.
  • If absent periods are linked to polycystic ovary syndrome (PCOS), and you are overweight as a result, losing weight may bring your periods back 
  • If absent periods are due to an underactive thyroid, treatment with thyroid hormone (thyroxine) may bring your periods back.

If the cause is premature ovary failure (a disorder of the ovary), you may be offered hormone replace therapy (HRT).

In some cases where the genitals have not developed properly, surgery can help.

Content provided by NHS Choices and adapted for Ireland by the Health A-Z.

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