PCOS explained: what the diagnosis actually means

If you have just been told you have polycystic ovary syndrome, the first useful thing to know is that the name is misleading. The “cysts” are not cysts. They are ordinary small follicles — the fluid-filled sacs every ovary makes each month — sitting in larger-than-usual numbers because ovulation has stalled partway rather than completing. Nothing is growing in there that shouldn’t be.

The second useful thing: a scan on its own cannot give you this diagnosis. Plenty of people have ovaries that look polycystic and do not have the syndrome. That single point causes more unnecessary alarm than almost anything else among the conditions we cover at HeliosCheck.com.

PCOS is common — the World Health Organization estimates it affects roughly 8 to 13 per cent of women of reproductive age, and that a large share go undiagnosed. Common does not mean trivial, and it does not mean the diagnosis should be made casually.

What the Rotterdam criteria actually say

Most clinicians in the UK, Europe and the US use the Rotterdam criteria. You need two of the following three — and other causes must have been excluded first.

Two of three. So irregular cycles plus clear androgen excess is PCOS even when the scan is completely normal — a combination that is routinely under-recognised. Equally, a suggestive scan plus one other feature is enough.

Two caveats matter. In anyone within about eight years of their first period, ultrasound should not be used as a criterion at all: young ovaries very often look polycystic normally, and irregular cycles are expected in that window. A firm diagnosis is usually deferred and reviewed later. Second, if a high-resolution scanner isn’t available the follicle-count threshold isn’t dependable; anti-Müllerian hormone (AMH) is increasingly used as a stand-in for the scan, though it is not yet a settled replacement.

Polycystic-looking ovaries are a finding, not a diagnosis. If your cycles are regular and you have no signs of androgen excess, a scan report using the word “polycystic” does not mean you have PCOS.

Why it is a diagnosis of exclusion

PCOS looks like several other things. Before anyone settles on it, a few conditions that are treated completely differently need ruling out:

• Thyroid disease. An underactive or overactive thyroid disturbs cycles and is corrected with treatment. A TSH is standard.
• High prolactin. Raised prolactin suppresses ovulation and can cause milky nipple discharge. Causes range from medication to a small benign pituitary adenoma.
• Non-classical congenital adrenal hyperplasia. An inherited enzyme difference that produces near-identical symptoms — irregular cycles and androgen excess. A 17-hydroxyprogesterone taken early in the cycle, ideally in the morning, screens for it. It is far less common than PCOS but genuinely matters, partly for inheritance.
• Rarer causes of androgen excess — Cushing’s syndrome, or an androgen-secreting tumour of the ovary or adrenal gland. These are uncommon, but rapid onset points towards them (see the urgent section below).

This is why a diagnosis made purely from a scan report, or purely from symptoms typed into a form, isn’t good enough. The blood tests are not box-ticking; they are how the other explanations get excluded.

The metabolic side that gets neglected

Most PCOS care is framed around periods and fertility. That framing quietly drops the part with the longest reach.

Insulin resistance sits underneath PCOS for a substantial proportion of people with it — and importantly, it occurs in lean women too, which is why “just lose weight” is both unkind and clinically incomplete. Higher insulin levels drive the ovary to make more androgen, which in turn worsens the cycle disruption. It is a loop, not a one-way street.

What follows from that is a raised long-term risk of type 2 diabetes, and often unfavourable lipids and blood pressure. None of this is inevitable, and none of it is a reason for alarm — it is a reason for a modest, boring monitoring schedule that most people never get offered.

This monitoring is worth doing regardless of whether you ever want children. That is the single most commonly missed point in PCOS care: the metabolic follow-up is not a fertility service, and it doesn’t stop mattering once your family is complete or if you never wanted one.

Protecting the lining of the womb

If you ovulate rarely, the lining of the womb is exposed to estrogen without the monthly progesterone that normally opposes it and sheds it. Over years, that can allow the lining to thicken abnormally — endometrial hyperplasia — and, uncommonly, progress further.

The practical rule most gynecologists work to — and one ACOG sets out for patients — is that if you are having fewer than about four bleeds a year, that should be addressed rather than ignored. It is straightforward to fix. A combined pill, a progestogen-only option, the hormonal coil, or cyclical progestogen for a few days every few months will all do the job; the choice depends on what else you want from it.

Any bleeding that is unusually heavy, prolonged or unpredictable deserves assessment rather than assumption — the pattern in PCOS can mask other causes. Our article on heavy periods and when to worry sets out where that line sits.

The levers that actually work

Movement. Regular activity improves insulin sensitivity and often cycle regularity, and it does so independently of any change on the scales. Resistance work alongside something aerobic is the combination with the best evidence. This is worth doing for its own sake, not as a weight-loss instrument.

Diet. No specific PCOS diet has proven superior to any other. What helps is a pattern you can actually sustain that steadies blood sugar. Where someone is carrying extra weight, even a modest loss can restore ovulation in a meaningful number of people — but that is offered as one option among several, never as a precondition for treatment.

The combined pill. The workhorse for cycle control, endometrial protection and androgen symptoms together. It does not treat insulin resistance, and it doesn’t “fix” PCOS underneath — it manages it, and symptoms usually return when it is stopped.

Metformin. Useful for the metabolic side, and it modestly helps cycle regularity for some people. Gastrointestinal side effects are common early and usually settle if the dose is built up slowly.

Letrozole. Now the first-line drug for inducing ovulation in PCOS, having overtaken clomifene on live birth rates in trial evidence. It must be prescribed and monitored properly, with scans in the early cycles — multiple pregnancy and over-response are real risks. Our fertility services page covers how that is arranged, and when to seek help trying to conceive covers the timing question.

Hair and skin. Mechanical hair removal, topical treatments, and anti-androgens such as spironolactone or cyproterone-containing pills where appropriate — these require reliable contraception. Improvement is slow by nature: hair follicles turn over across months, so three to six months is the honest expectation, not weeks.

Inositol supplements. Popular, and the evidence is genuinely mixed: some encouraging small studies, no firm conclusion on live birth, and no place yet in the NHS treatment guidance. Low risk, not a substitute for the above. If someone wants to try it, we say so plainly rather than either endorsing or dismissing it.

When to seek urgent or same-day care

Most of PCOS is managed unhurriedly. These are the exceptions:

• Rapid onset of androgen features — hair growth, voice deepening or clitoral enlargement developing over weeks to months rather than years. This suggests a different cause and needs prompt investigation.
• Bleeding soaking through a pad or tampon every hour for several hours, or bleeding with dizziness, breathlessness or fainting.
• Symptoms of very high blood sugar — marked thirst, passing large volumes of urine, unexplained weight loss, blurred vision, drowsiness or vomiting. Same day.
• Sudden severe one-sided pelvic pain, particularly with nausea or vomiting.
• A positive pregnancy test with pain or bleeding — needs same-day assessment to exclude ectopic pregnancy.
• On ovulation induction: rapid abdominal swelling, sharp weight gain over days, or breathlessness — possible ovarian hyperstimulation.
• Any bleeding after the menopause, which is never part of PCOS and always needs investigation.

The part that isn’t in the leaflet

A PCOS diagnosis often lands as a package of losses: fertility worries, appearance, a body that feels uncooperative. Rates of depression, anxiety and disordered eating are higher in people with PCOS than without, and that is not a character flaw or an overreaction — it is part of the condition’s footprint. It also deserves treatment in its own right, not as an afterthought once the bloods are sorted.

It’s worth saying clearly: PCOS is manageable, most people with it who want children do have them, and the diagnosis is not a verdict on your future. But nobody has to be cheerful about it on day one.

What a consultation would actually cover

A first PCOS appointment at HeliosCheck.com is mostly listening, then narrowing. Expect to go through your cycle pattern over the past year, the timeline of any hair or skin changes, medication history, and family history of type 2 diabetes or PCOS. We’ll agree which bloods you need and when in the cycle to take them, since timing changes the interpretation, and arrange them locally.

We will be direct about the limits. An online consultation cannot perform a physical or internal examination, and it cannot perform the ultrasound. Where a scan or examination is needed, we arrange it and then review the results with you — how it works explains that pathway. Nobody is diagnosed on a video call alone.

You should leave with a written plan covering three things: what is being done about cycles and endometrial protection, what metabolic monitoring is scheduled, and what happens next if you are trying to conceive or expect to in future. If anything in that plan is unclear, our frequently asked questions may help, or bring it back at review.