How is PCOS diagnosed? The Rotterdam criteria, blood tests, ultrasound, and how to prepare for your appointment with documented cycle data.
PCOS takes an average of 2 years to diagnose. Part of the reason is that it's diagnosed by pattern — a combination of criteria rather than a single test. Understanding how diagnosis works helps you advocate for yourself and bring the right information to your appointment.
PCOS is diagnosed using the Rotterdam criteria (established in 2003 and still the global standard). A diagnosis requires meeting at least 2 of the following 3 criteria:
| Criterion | What it means | How it's assessed |
|---|---|---|
| 1. Irregular or absent ovulation | Cycles over 35 days, under 21 days, or absent | Cycle history + BBT chart |
| 2. Clinical or biochemical androgen excess | High testosterone on blood test, or acne/hirsutism/hair loss | Blood tests + clinical exam |
| 3. Polycystic ovarian morphology | 12+ small follicles per ovary on ultrasound (or enlarged ovarian volume) | Transvaginal or transabdominal ultrasound |
You do not need all three — two are sufficient for a PCOS diagnosis. And importantly, you do not need to have "polycystic ovaries" on ultrasound to be diagnosed with PCOS.
| Test | What it checks | Notes |
|---|---|---|
| Total testosterone (or free androgen index) | Androgen excess | Best done in the morning, days 2–5 of cycle |
| LH and FSH | LH:FSH ratio (elevated in PCOS) | Days 2–5 of cycle for accuracy |
| TSH (thyroid) | Rule out thyroid cause of irregular cycles | Any time |
| Prolactin | Rule out high prolactin as cause | Fasting, morning blood draw |
| Fasting glucose + insulin | Insulin resistance assessment | Fasted (no food 8+ hours) |
| DHEAS | Adrenal androgen (rules out adrenal cause) | Any time |
| AMH (anti-Mullerian hormone) | Ovarian reserve — often elevated in PCOS | Any time in cycle |
Criterion 1 (irregular ovulation) is assessed primarily through your cycle history. A single appointment where you say "my periods are irregular" is easy to dismiss. Six months of documented cycle data — showing cycles of 38, 52, and 44 days, with symptom logs — is far harder to dismiss and significantly speeds up the diagnostic process.
This is the practical value of cycle tracking: it turns your lived experience into medical evidence.
Be specific. Instead of "my periods are irregular," say: "Over the last 6 months, my cycle lengths have been [X, X, X, X] days. I've been logging symptoms including [acne pattern, energy crashes, weight changes] since [date]. I'd like blood tests for testosterone, LH/FSH, TSH, prolactin, and fasting insulin, and a referral for a pelvic ultrasound."
If your GP doesn't take you seriously, you are entitled to a second opinion or a self-referral to a gynaecologist in many health systems.
Before confirming PCOS, a doctor should rule out:
This is why multiple blood tests are needed — PCOS is a diagnosis of exclusion as well as of pattern.
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Start tracking →PCOS diagnosis typically involves blood tests (testosterone, LH, FSH, thyroid function, prolactin, fasting insulin or glucose) and a pelvic ultrasound to look for multiple small follicles on the ovaries. There is no single definitive PCOS test — diagnosis is based on meeting at least 2 of 3 Rotterdam criteria.
The Rotterdam criteria (used globally since 2003) require at least 2 of: (1) irregular or absent ovulation, (2) clinical or biochemical signs of androgen excess (high testosterone, acne, hirsutism), (3) polycystic ovarian morphology on ultrasound. You don't need all three.
Yes. The ultrasound criterion is just one of three Rotterdam criteria. If you have irregular periods and clinical signs of high androgens (acne, hirsutism), you can be diagnosed with PCOS even if your ultrasound looks normal.
Ask your GP for: total testosterone (or free androgen index), LH and FSH (ideally done on days 2–5 of your cycle), fasting glucose and insulin, thyroid function (TSH), prolactin, and DHEAS. Some GPs may not order all of these — bring a list and advocate for what you need.