Premature Ovarian Insufficiency (POI) is the loss of ovarian function before age 40. In short: if you are under 40, your periods have become infrequent or stopped, and you notice hot flushes or vaginal dryness, ask for a medical assessment — early diagnosis and hormone therapy protect your bones, heart and quality of life for decades to come.

What POI is — and why it is no longer called "premature menopause":

POI is a distinct condition with its own guidelines (NICE, ESHRE, The Menopause Society), not an early version of natural menopause. The key difference is that ovarian function does not stop for good. It can be intermittent — some women resume periods, and a small minority can conceive spontaneously. That is why the term "insufficiency" is preferred over "premature menopause", which implies a complete, permanent stop.

How common it is:

POI affects about 1% of women under 40 and roughly 0.1% of women under 30. It can appear at any age below 40, including the teenage years, and it is often missed or diagnosed late because the symptoms are put down to stress or minor irregularities.

Causes:

In most cases no clear cause is found. The known causes fall into a few groups: genetic — the best-recognised being the FMR1 gene premutation, though other changes on the X chromosome exist; autoimmune — the immune system attacks the ovaries, often alongside autoimmune thyroid disease or adrenal insufficiency; and iatrogenic — chemotherapy, pelvic radiotherapy, or surgical removal of the ovaries. Infection can contribute but is rare. If you are under 30 or have a family history, your doctor may suggest genetic testing and a karyotype.

Why the ovaries stop early:

The ovaries hold a fixed number of eggs from before birth, and that number falls through life until none remain. POI is what happens when the supply runs out, or stops working, far earlier than usual. Sometimes the follicles are gone. Sometimes they are still there but do not respond to the signals that would normally make them mature.

The second possibility explains a great deal about POI. Because the ovary is not responding, it is not producing oestrogen, and there is nothing to tell the pituitary gland to hold back. The pituitary responds by pushing harder, and the level of follicle-stimulating hormone rises. That is why a raised FSH is the central clue: it is the brain's attempt to drive an ovary that is not answering.

It also explains why the condition can be intermittent. If some follicles remain and respond occasionally, the ovary may produce oestrogen in bursts, a period may arrive, and a test taken in that window can look different from one taken a month later.

Symptoms:

The main sign is a disturbed cycle: periods that are infrequent or absent for at least 4 months. You may also notice hot flushes and night sweats, vaginal dryness and discomfort with intimacy, restless sleep, mood changes, lower libido, and fatigue. Some women never have flushes — the first sign is simply that periods stop. Because ovarian function can be intermittent, symptoms can come and go.

How it is diagnosed:

In a woman under 40 with oligo/amenorrhoea for at least 4 months, the diagnosis is confirmed by two FSH measurements above 25 IU/L taken 4-6 weeks apart. A single measurement is not enough, precisely because function can fluctuate. Oestradiol is usually checked too, and AMH, a karyotype, or FMR1 testing can help identify a cause. Pregnancy tests and thyroid/prolactin checks rule out other reasons for missed periods before the diagnosis is made.

What else stops periods before 40:

Missing periods at this age has a long list of ordinary explanations, and POI is not the first one to rule out.

  • Pregnancy, which is the first thing to check and remains possible even when cycles have been irregular
  • The combined contraceptive pill and some other hormonal methods, which can stop withdrawal bleeds and mask what the ovaries are doing
  • Polycystic ovary syndrome, where cycles become infrequent rather than stopping
  • An overactive or underactive thyroid
  • A raised prolactin level, which can interrupt the cycle and sometimes causes milk production
  • Significant weight loss, restrictive eating, or a very high training load, any of which can switch the cycle off
  • Severe stress, or a recent illness
  • Treatment that affects the ovaries, including chemotherapy and radiotherapy
  • The years immediately before natural menopause, though this would be unusual under 40

Several of these can be present at once, which is one reason a single appointment may not settle the question.

How POI is separated from those causes:

The tests that identify POI are looking for a specific combination.

What distinguishes it is a period that has stopped or become very infrequent, together with blood tests showing that the ovaries are not producing oestrogen and that the pituitary is working hard to compensate. Because both can fluctuate, one set of results is not enough — which is exactly why the second test matters. The gap between the two tests is deliberate, not bureaucratic.

Other features help. POI usually brings symptoms of low oestrogen at the same time — flushes, night sweats, dryness, disturbed sleep. Where periods have stopped but nothing else has changed, other explanations become more likely. A family history of early menopause, or a personal history of chemotherapy, radiotherapy or ovarian surgery, shifts the balance further.

It is worth saying plainly: a diagnosis should not be given on the basis of one blood test. If it has been, ask for the second.

Treatment:

NICE and ESHRE recommend hormone therapy (HRT) for women with POI unless there is a contraindication. At this age the benefits outweigh the risks by a wide margin. The goal is to replace oestrogen until around the average age of natural menopause (about 51), not just for a few years. If you have a uterus, oestrogen must be combined with a progestogen to protect the uterine lining. Doses sometimes need to be higher than those used at natural menopause. The combined contraceptive pill is an acceptable alternative if you also want contraception.

Fertility:

Egg or embryo freezing should be discussed as soon as you are diagnosed — the window can be short and ovarian function is unpredictable. Spontaneous pregnancy is possible but rare. The most reliable path is IVF with donor eggs. If you want children, see a fertility specialist early rather than waiting.

Long-term health:

Without oestrogen, women with POI have a higher risk of osteoporosis, cardiovascular disease and possibly cognitive decline. HRT taken until around age 51 lowers these risks. A bone density scan (DEXA) at diagnosis and then as guided by risk, adequate calcium and vitamin D, and weight-bearing exercise are part of routine care, along with cardiovascular checks such as blood pressure and lipids.

What to bring to the first appointment:

  • Your cycle history: when your periods were regular, when they changed, and whether they stopped altogether or came and went
  • The dates of your last few periods, as precisely as you can
  • Any flushes, night sweats, dryness, sleep problems or mood changes, and when they began
  • A family history of early menopause, and any known genetic conditions
  • Your own history of chemotherapy, radiotherapy, or surgery involving the ovaries
  • Everything you take, including contraception, which can affect what the tests show
  • Whether you want children, now or in the future

Dates rather than impressions matter here. 'My periods have been all over the place' and 'my last three were months apart' lead to different conversations, and the second is the one that gets the tests ordered.

Questions worth asking after diagnosis:

  • How certain is the diagnosis, and were two sets of tests taken?
  • Do I still need contraception, and for how long?
  • How long will I take hormone therapy, and how will that be reviewed?
  • Is the dose right for someone my age, or does it need adjusting?
  • Do I need a bone density scan, and how often should it be repeated?
  • What will be monitored long term — bones, heart, blood pressure, cholesterol?
  • What are my options if I want children, and how soon do I need to decide?
  • Who can I talk to about how this feels?

That last question is not an afterthought. A diagnosis at this age carries a loss that has nothing to do with hormones, and it deserves as much attention as the blood tests. Ask who can help with it, and take the answer seriously.

Where POI guidance is firm and where it is open:

The main outline is settled. POI is a distinct condition, the diagnosis rests on repeated hormone measurements rather than a single one, and hormone therapy is recommended until around the age of natural menopause unless there is a reason not to use it. The long-term risks to bone and the heart are recognised, and checking for them is part of routine care.

What is less settled is the detail. How far a woman's dose should differ from a standard menopausal dose, and how that should be judged, varies in practice. How often bone density should be repeated when the first scan is normal is a matter of judgement rather than a fixed rule. And when no cause is found — which is the usual outcome — how far to keep looking is debated, especially when the answer would not change the treatment.

The practical implication is simple. The decisions that matter are rarely about which guideline is right. They are about whether your treatment is adequate, and whether anyone is following you up.

Beliefs about POI worth correcting:

  • 'It is just an early menopause.' It is a different diagnosis. Ovarian function can return intermittently, and the treatment differs — in dose and in how long it lasts.
  • 'I am too young for hormone therapy.' At this age the balance of benefit and risk is more favourable than at natural menopause, not less. The reason to take it is protection, not symptom relief alone.
  • 'If my periods come back, I am cured.' A returning period means some follicles are still responding. It does not mean the diagnosis was wrong, and it does not mean treatment should stop.
  • 'Hormone therapy will delay the menopause.' It replaces what the ovaries are not making. It does not postpone the underlying condition.
  • 'I cannot have children.' Spontaneous pregnancy is possible but uncommon, and donor eggs are a reliable route. Both deserve a conversation, and an early one.
  • 'Nothing can be done about the long-term risks.' Bone and heart risk are precisely what treatment and monitoring are for.

When to ask for help:

Any stop of periods under age 40 for 4 months deserves an assessment, especially if it comes with flushes or vaginal dryness. It is not "too early", and it will not simply pass. If you had cancer treatment, ask about monitoring your ovarian function. The emotional side is real — a POI diagnosis can bring grief about fertility and identity; counselling and peer support help.

In short:

POI is the loss of ovarian function under 40, with possible intermittent function. Diagnosis rests on two FSH readings above 25 IU/L, 4-6 weeks apart. Standard care is HRT until about age 51. Discuss fertility early. It is a manageable condition — but not one to ignore.