The Rotterdam Criteria for PCOS, Explained Plainly

If a doctor mentioned the Rotterdam criteria for PCOS and you left the appointment thinking, “Lovely, another phrase I now have to decode in my spare time,” this is for you. The Rotterdam criteria are not a quiz you pass or fail at home. They are a clinical framework a doctor uses to decide whether your symptoms, blood tests and sometimes ultrasound findings fit PCOS. The short version is surprisingly simple: there are three main features, and a clinician usually needs two of the three after ruling out other causes.

What is PCOS, briefly?

PCOS, or polycystic ovary syndrome, is a common hormone-related condition that can affect ovulation, skin, hair growth, metabolism and long-term health. You may also see the newer name PMOS, polyendocrine metabolic ovarian syndrome, after a May 2026 international consensus renamed the condition to better reflect that it is more than “cysts on ovaries.” Estimates vary, but PCOS is often described as affecting around 1 in 10 women, with newer global work putting it closer to 1 in 8. It is under-diagnosed, frequently misunderstood and, importantly, manageable with the right medical support.

The three Rotterdam criteria for PCOS, in plain language

The Rotterdam criteria were created so clinicians had a shared way to diagnose PCOS. They look for three clusters: irregular or absent ovulation, signs of higher androgens, and polycystic ovarian appearance on ultrasound. “Polycystic” is a historically confusing word here. The follicles seen on ultrasound are usually small egg-containing follicles, not dangerous cysts.

The key idea: a doctor does not need to find all three. In adults, PCOS can usually be diagnosed when two of the three are present, other explanations have been checked, and the full clinical picture fits. That last part matters. Rotterdam is a clinical tool, not a self-diagnosis checklist.

1. Irregular or absent ovulation

Ovulation is when an ovary releases an egg. If ovulation happens irregularly, periods often become irregular too. In real life, that can look like cycles longer than about 35 days, periods that vanish for months, or fewer than eight periods in a year. Some people bleed unpredictably rather than simply “late.” Others have a period most months but do not ovulate consistently, which is deeply unfair of the body but not unheard of.

What a doctor checks usually starts with your cycle history. They may ask how old you were when your periods started, how many bleeds you have each year, whether your cycle length has changed, what contraception you use, and whether pregnancy, thyroid problems, high prolactin, stress, weight change, perimenopause or other conditions could explain the pattern.

They may also order a progesterone blood test to check whether ovulation likely happened. People often call this a “day-21 progesterone” test, but that name assumes a 28-day cycle. If your cycles are longer, the useful timing is often around seven days before an expected period. With irregular cycles, your clinician may need to time the test differently or repeat it.

This is where tracking can be genuinely useful. A few months of dates, bleeding patterns, acne flares, hair changes, mood, energy and possible ovulation signs can give a GP or gynaecologist a much clearer story than “my cycle is weird,” even though “my cycle is weird” is a valid opening sentence.

2. Signs of high androgens

Androgens are hormones such as testosterone. Everyone has them, but in PCOS they can be higher or act more strongly in the body. Clinicians look for two kinds of evidence: clinical hyperandrogenism, meaning visible signs, and biochemical hyperandrogenism, meaning blood-test evidence.

Visible signs can include darker or thicker hair growth on the chin, upper lip, chest, abdomen or thighs; persistent adult acne; oily skin; and scalp hair thinning in a pattern that feels a little too “why is my parting wider than last year?” These signs can be emotionally loaded. You are allowed to want a medical explanation without wanting your face, hair or skin discussed like a lab specimen.

What a doctor checks may include a skin and hair history, sometimes a hirsutism score, and blood tests. Useful bloods often include total or free testosterone and SHBG, which stands for sex hormone-binding globulin. SHBG acts a bit like a hormone taxi service; when it is lower, more testosterone can be available to tissues. Depending on your situation, your clinician may also check DHEAS, androstenedione, thyroid function, prolactin, 17-hydroxyprogesterone or other markers to rule out adrenal or pituitary causes.

One important caveat: androgen testing is not perfect. Results can vary by lab method, contraception, cycle timing and medication. A normal blood test does not always erase obvious clinical signs, and visible signs do not automatically mean PCOS. The job is to put the puzzle pieces together carefully.

3. Polycystic ovaries on ultrasound

The third Rotterdam feature is polycystic ovarian morphology, usually checked by ultrasound. In the original Rotterdam definition, this meant at least 12 small follicles measuring 2-9 mm in one ovary, or an ovarian volume greater than 10 ml. Newer ultrasound machines can see much more detail, so some modern guidelines use higher follicle-count thresholds. Translation: do not panic if you see slightly different numbers across medical websites. Your clinician should use the guideline and ultrasound method that fits your setting.

The ultrasound does not “diagnose PCOS” by itself. Some people have polycystic-looking ovaries without PCOS. Some people have PCOS without the classic ultrasound appearance. And if you are an adolescent, clinicians are usually more cautious with ultrasound because ovaries can naturally look multi-follicular in the years after periods begin.

What the doctor sees is usually a pattern of many small follicles around the ovary and/or increased ovarian volume. These are not the same thing as big painful ovarian cysts. They are often follicles that started developing but did not move through a regular ovulation pattern.

Why you only need 2 of 3

This is the part that trips people up. You can meet Rotterdam criteria for PCOS without polycystic ovaries on ultrasound if you have irregular ovulation and signs of high androgens. You can also meet them with irregular ovulation and polycystic ovaries, even if androgen signs are not obvious. Or you can meet them with androgen signs and polycystic ovaries, even if bleeding looks more regular.

That “2 of 3” rule matters because PCOS does not show up the same way in every body. It also stops the ultrasound from becoming the main character. A normal ultrasound does not automatically close the conversation if your cycle and androgen picture are strong. A polycystic-looking ovary does not automatically settle it if the rest of the picture does not fit.

What the Rotterdam criteria do not tell you

The Rotterdam criteria help doctors decide whether the diagnostic pattern fits PCOS. They do not diagnose insulin resistance, explain every symptom, measure cardiovascular risk, or catch every condition that can mimic PCOS. They also do not replace a proper differential diagnosis. Adrenal conditions, thyroid disease, high prolactin, hypothalamic amenorrhoea, medication effects, perimenopause and rare androgen-secreting tumours can all sit in the “please rule me out” category.

There are also other criteria sets. NIH criteria are narrower and focus on ovulatory dysfunction plus hyperandrogenism. AE-PCOS criteria put androgen excess more centrally. Rotterdam is broader, which means it may identify more people, but it can also create more variation inside the diagnosis. That is why a good clinician does not stop at a label. They ask: what pattern do you have, what else needs checking, and what support actually fits your body?

What to do next

First, track your cycle and symptoms for 2-3 cycles if you can. Note bleed dates, cycle length, acne, chin or body hair changes, scalp shedding, pelvic pain, cravings, sleep, mood, energy, weight changes and anything that seems to repeat. If your periods are missing for several months, do not wait forever just to make a neat spreadsheet. Medical care beats a perfect tracker.

Second, book a GP or gynaecology appointment and be direct. You can say: “My periods are irregular and I have [acne / chin hair / hair thinning / missed periods / symptoms that fit you]. I’d like to be screened against the Rotterdam criteria for PCOS and to rule out other causes.”

Third, use symptom tools as preparation, not proof. Belle’s free PCOS self-test can help you organise the pattern of what you are noticing, but it does not diagnose PCOS. Think of it as a way to walk into the appointment with clearer notes, not a verdict from the internet wearing a tiny white coat.

If tracking is part of your next step, Belle’s guides to choosing a PCOS tracker and tracking ovulation with PCOS can help you decide what is worth recording without turning your life into a data-entry internship.

FAQ

Can I have PCOS without all three Rotterdam criteria?

Yes. In adults, doctors usually look for 2 of the 3 Rotterdam criteria after ruling out other causes: irregular or absent ovulation, signs of high androgens, and polycystic ovaries on ultrasound. You do not need all three for a clinician to consider PCOS.

Do I need an ultrasound to be diagnosed with PCOS?

Not always. If you have irregular ovulation and clear clinical or blood-test signs of high androgens, a doctor may not need ultrasound to meet Rotterdam criteria. Ultrasound can still be useful in some cases, especially when the picture is unclear.

What's the difference between Rotterdam, NIH, and AE-PCOS criteria?

Rotterdam criteria are broader and require 2 of 3 features. NIH criteria are narrower and focus on ovulatory dysfunction plus hyperandrogenism. AE-PCOS criteria put androgen excess at the centre of the diagnosis. Your clinician may use these frameworks differently depending on age, symptoms and local guidance.

Can the Rotterdam criteria miss PCOS?

They can miss or complicate some cases, especially when symptoms are mild, lab tests are borderline, contraception is masking signs, or another condition overlaps. They can also include different PCOS patterns under one label. That is why clinical context and follow-up matter.

How accurate is a PCOS symptom quiz?

A PCOS symptom quiz can be useful for organising what you are experiencing, but it cannot confirm or rule out PCOS. Diagnosis needs a clinician, medical history, blood tests and sometimes ultrasound, plus checks for other causes.

References

1. Rotterdam ESHRE/ASRM-sponsored PCOS consensus workshop group – Revised 2003 consensus on diagnostic criteria and long-term health risks related to PCOS. Original Rotterdam consensus criteria.
2. International evidence-based guideline for the assessment and management of PCOS, 2018. International guideline led by Monash/ESHRE/ASRM partners.
3. International evidence-based guideline for the assessment and management of polycystic ovary syndrome, 2023. Updated diagnostic and management recommendations.
4. Endocrine Society – Polyendocrine Metabolic Ovarian Syndrome name change, 2026. Current naming context for PCOS/PMOS.