Amenorrhoea: Causes of Missing or Absent Periods

10 min read
Amenorrhoea: Causes of Missing or Absent Periods

Amenorrhoea means not having menstrual periods.

Sometimes that’s completely expected, such as during pregnancy, while breastfeeding, after menopause or with some forms of hormonal contraception.

At other times, absent periods are a sign that ovulation or reproductive hormone signalling has been disrupted.

PCOS, low energy availability, significant changes in exercise or nutrition, stress, thyroid conditions, high prolactin levels and premature ovarian insufficiency are just some of the possible causes.

A missed period here and there isn’t necessarily amenorrhoea. But if periods haven’t started by the expected stage of puberty or periods that were previously regular stop for several months, it’s worth finding out why.

Key takeaways

  • Amenorrhoea means the absence of menstrual periods.
  • Primary amenorrhoea refers to periods that haven’t started by the expected stage of puberty.
  • Secondary amenorrhoea generally means periods have stopped for 3 months or more after previously occurring regularly.
  • Pregnancy is the first possibility to rule out if pregnancy is possible.
  • Common causes include PCOS, low energy availability, significant exercise or dietary changes, stress, thyroid disease, high prolactin and premature ovarian insufficiency.
  • Treatment depends on the underlying cause rather than simply trying to make a period happen.
  • Some causes of amenorrhoea can affect bone health, fertility or the uterine lining if they continue untreated.

On this page

What is amenorrhoea?

Amenorrhoea is the medical term for an absence of menstrual periods.

It isn’t a disease in itself. It is a symptom or menstrual pattern that can have many different explanations.

Doctors generally divide it into two categories:

  • Primary amenorrhoea: periods haven’t started by the expected stage of puberty.
  • Secondary amenorrhoea: periods previously occurred but have now stopped.

Before investigating other causes of secondary amenorrhoea, pregnancy is usually ruled out where pregnancy is possible.

What is primary amenorrhoea?

Primary amenorrhoea means menstruation hasn’t started by the age when it would normally be expected.

Guidance varies slightly in the exact age used. The Royal Children’s Hospital Melbourne recommends specialist referral for primary amenorrhoea at age 15, while other Australian health information describes assessment at around age 16 or if menstruation hasn’t begun more than three years after breast development starts.

Earlier assessment may be appropriate if other signs of puberty haven’t developed. For example, absence of breast development by age 13 should be assessed.

Possible causes of primary amenorrhoea include:

  • constitutional or familial later puberty
  • low energy availability or undernutrition
  • chronic illness
  • hormonal conditions affecting the brain, pituitary gland or ovaries
  • congenital differences in reproductive anatomy
  • some genetic conditions

A teenager who hasn’t started periods doesn’t need to work out which of these applies on their own. A GP can assess pubertal development and arrange appropriate testing or referral.

What is secondary amenorrhoea?

Secondary amenorrhoea generally refers to periods stopping for 3 months or more in someone who previously menstruated regularly.

It is different from having one unexpectedly long cycle.

If your period is simply a few days or weeks late, start with our guide to a late period when you aren’t pregnant.

When are absent periods expected?

Not every absence of bleeding represents a menstrual disorder.

Periods normally stop during pregnancy.

They may also be absent:

  • while breastfeeding
  • after menopause
  • with some hormonal contraceptive methods

Hormonal IUDs, contraceptive implants and contraceptive injections can reduce or completely stop bleeding in some people.

This doesn’t necessarily mean something is wrong.

It’s still worth taking a pregnancy test if pregnancy is possible and your bleeding pattern unexpectedly changes.

What causes amenorrhoea?

Outside pregnancy, breastfeeding, menopause and expected contraceptive effects, common causes include:

PCOS

PCOS can interfere with regular ovulation.

Some people with PCOS menstruate occasionally rather than monthly, while others may go several months without a period.

Acne, increased facial or body hair, scalp hair thinning and difficulty becoming pregnant may occur too, although symptoms vary considerably.

Functional hypothalamic amenorrhoea

Functional hypothalamic amenorrhoea occurs when hormonal signalling from the brain to the ovaries is suppressed.

This may be associated with:

  • low energy availability
  • restrictive eating
  • significant weight loss
  • high levels of exercise
  • significant psychological stress

Someone does not need to be underweight or have a diagnosed eating disorder for low energy availability to affect menstruation.

Thyroid conditions

Both underactive and overactive thyroid conditions can interfere with menstrual cycles and ovulation.

High prolactin

Prolactin is the hormone involved in breast milk production.

Higher-than-expected prolactin levels outside pregnancy and breastfeeding can suppress reproductive hormone signalling and stop periods.

This may occasionally be related to medicines or a pituitary condition.

Premature ovarian insufficiency

Premature ovarian insufficiency, or POI, occurs when ovarian activity is reduced before age 40.

Periods may become irregular or stop, and symptoms such as hot flushes or vaginal dryness may occur.

POI is different from ordinary menopause because ovarian activity can sometimes occur intermittently.

Scarring inside the uterus

Rarely, scar tissue inside the uterus can interfere with menstruation.

This is known as Asherman syndrome and can occur after some uterine procedures or pregnancy-related complications.

Other medical conditions or medicines

Chronic illness and some medicines can also affect the hormonal pathways controlling menstruation.

This is why your doctor will usually ask about your general health and medications rather than looking only at the reproductive system.

Amenorrhoea, exercise and low energy availability

Missing periods in athletes was once sometimes treated as an almost normal consequence of intensive training.

It isn’t anymore. If the body repeatedly doesn’t receive enough energy to cover exercise and normal physiological functions, reproductive hormone production can be reduced.

This forms part of a broader condition known as Relative Energy Deficiency in Sport (RED-S).

Amenorrhoea associated with low oestrogen and low energy availability matters because it can affect bone formation and increase the risk of bone stress injuries.

If your periods have stopped alongside a significant increase in training, restrictive eating or recurring injuries, speak with a doctor or sports dietitian rather than simply assuming it is the price of being fit.

How is amenorrhoea diagnosed?

Your doctor will usually start by asking about:

  • when your periods started
  • your usual cycle
  • when your last period occurred
  • pregnancy possibility
  • contraception
  • exercise
  • nutrition and changes in weight
  • stress
  • medications
  • other symptoms

Testing depends on your individual situation but may include:

  • a pregnancy test
  • thyroid tests
  • prolactin
  • follicle-stimulating hormone (FSH)
  • luteinising hormone (LH)
  • oestrogen levels
  • androgen tests where appropriate
  • pelvic ultrasound

Further imaging or specialist assessment may occasionally be needed.

Why does amenorrhoea matter?

Not having to deal with a monthly period might initially sound convenient, particularly if your periods used to be painful or heavy.

But unexplained amenorrhoea can be an important clue about your health.

Bone health

When amenorrhoea is associated with persistently low oestrogen, particularly from low energy availability or ovarian insufficiency, bone density can be affected.

This is especially important during adolescence and early adulthood, when peak bone mass is still developing.

The uterine lining

A different issue can occur with conditions such as PCOS.

If ovulation happens infrequently, the uterine lining may be exposed to oestrogen without regular progesterone exposure and shedding.

Over time, very infrequent periods can increase the risk of excessive endometrial thickening in some people.

Fertility

Amenorrhoea can also indicate that ovulation isn’t happening regularly, which can make pregnancy more difficult.

The effect on fertility depends entirely on why your periods have stopped.

How is amenorrhoea treated?

There isn’t one treatment for amenorrhoea because the goal is to address the cause.

Treatment may involve:

  • adjusting nutrition and restoring adequate energy availability
  • changing an exercise programme where appropriate
  • support for an eating disorder
  • treating a thyroid or pituitary condition
  • managing PCOS
  • hormonal treatment where appropriate
  • treatment for premature ovarian insufficiency
  • surgery for particular anatomical causes

If fertility is the main concern, treatment may also include specific approaches to restore or induce ovulation.

The important point is that treatment should be matched to the reason periods have stopped rather than simply prescribing something to create bleeding.

Can you get pregnant if you have amenorrhoea?

It depends on whether ovulation is occurring.

If you aren’t ovulating, spontaneous pregnancy can’t occur during that particular cycle because there is no egg available for fertilisation.

But ovulation can sometimes return unexpectedly before the next visible period.

This means amenorrhoea shouldn’t be relied on as contraception unless the absence of ovulation is part of a contraceptive method being used correctly.

If you want to become pregnant and your periods are absent, you don’t need to wait a year before asking for fertility advice. Irregular or absent ovulation is already a reason to discuss fertility with your doctor.

Learn more about anovulation and pregnancy.

When should you see a doctor?

Arrange an appointment if:

  • your first period hasn’t started by around age 15 to 16
  • breast development hasn’t begun by age 13
  • previously regular periods have stopped for 3 months or more
  • your periods are consistently very infrequent
  • you have around 8 or fewer periods per year
  • you have symptoms such as hot flushes well before the usual age of menopause
  • your periods have stopped alongside restrictive eating or intensive exercise
  • you’re trying to become pregnant and periods are absent
  • you have headaches, vision changes or unexpected milk-like nipple discharge

You can use Period Shop’s period tracker to record cycle dates and symptoms to take to your appointment.

Frequently asked questions

Is missing one period amenorrhoea?

Not usually. A single late or missed period can occur for many reasons. Secondary amenorrhoea generally refers to periods stopping for at least 3 months after previously being regular.

What is the most common cause of a missed period?

If pregnancy is possible, pregnancy should be ruled out first. Beyond pregnancy, causes include changes in ovulation, PCOS, stress, low energy availability, thyroid conditions, breastfeeding and hormonal contraception.

Can stress stop your period?

Significant stress can disrupt the brain-hormone signalling involved in ovulation and can contribute to functional hypothalamic amenorrhoea. Persistent absent periods still deserve assessment rather than automatically being attributed to stress.

Can too much exercise stop periods?

Exercise itself isn’t necessarily the problem. Amenorrhoea is more likely when high training demands combine with inadequate energy intake and other physical or psychological stressors.

Is it unhealthy not to have periods?

It depends why periods are absent. Having no bleeding because of pregnancy, menopause or some hormonal contraceptives can be completely expected. Unexplained amenorrhoea may signal a hormonal or health issue and some causes can affect bones, fertility or the uterine lining.

Can periods stop with PCOS?

Yes. PCOS can cause infrequent or absent ovulation, which may lead to widely spaced or missing periods.

Does amenorrhoea mean you are infertile?

No. Amenorrhoea is a symptom, not a diagnosis of permanent infertility. Fertility depends on the underlying cause and whether ovulation can occur spontaneously or with treatment.

Can you ovulate without getting a period first?

Yes. Ovulation occurs before menstruation, so it is possible to ovulate and become pregnant before the first period returns after a period of amenorrhoea.

Missing periods are information, not just an inconvenience

If your periods have disappeared unexpectedly, the goal isn’t simply to make them come back.

It’s to understand what has changed in the hormonal system that normally produces your menstrual cycle.

For some people the answer is relatively straightforward. For others, missing periods provide an important clue to PCOS, low energy availability, thyroid disease, ovarian function or another condition that deserves treatment.

Related reading

Sources and further reading

This article provides general educational information and isn’t a substitute for individual medical advice.