PCOS Basics: Understanding Diagnostic Criteria
NIH, Rotterdam, AE-PCOS - which one is right?
Welcome to PCOS Basics series - a guide to Polycystic Ovary Syndrome. Whether you’ve just been diagnosed, think you might have PCOS, or simply want to understand it better, this series walks you through diagnosis, symptoms, treatment, and long-term health so you can feel informed and in control.
If you’ve been Googling your symptoms late at night - irregular periods, unexplained weight fluctuations, acne that won’t quit, excess hair growth - you’ve probably stumbled across PCOS. But here’s what’s confusing: PCOS diagnosis isn’t straightforward. There’s no single test that definitively says “yes” or “no.”
Instead, doctors use a set of diagnostic criteria, and the most widely accepted are the Rotterdam criteria. Let’s break down exactly what these are, how they work, and what you need to know about getting diagnosed.
Why Is PCOS Diagnosis Complicated?
Unlike many conditions, PCOS doesn’t have a single biomarker or definitive test. You can’t just check one hormone level or run one scan and get a clear answer.
PCOS is a syndrome - a collection of symptoms and signs that tend to occur together. This means diagnosis requires piecing together clinical evidence from:
Your menstrual history
Physical exam findings
Blood work
Ultrasound imaging
Ruling out other conditions that can mimic PCOS
Different medical organisations have also proposed different diagnostic criteria over the years, which adds to the confusion.
The Three Main Diagnostic Criteria Sets
1. NIH Criteria (1990) – The Original
The most restrictive criteria, requiring BOTH:
Chronic anovulation (irregular or absent ovulation)
Clinical or biochemical signs of hyperandrogenism (excess male hormones)
2. Rotterdam Criteria (2003) – The Current Gold Standard
The most widely used criteria globally. You need 2 out of 3 of the following:
Irregular or absent ovulation
Clinical or biochemical signs of hyperandrogenism
Ultrasound findings of polycystic-appearing ovaries or elevated anti-Müllerian hormone (AMH) levels (the second part was only added in 2023 - watch a useful recap here)
3. Androgen Excess Society (AE-PCOS) Criteria (2006)
A middle ground, requiring:
Hyperandrogenism (clinical or biochemical) PLUS
Ovarian dysfunction (irregular ovulation) OR polycystic ovaries
For the rest of this post, I’ll focus on the Rotterdam criteria since they’re the most commonly used worldwide.
Next week, we’ll review latest findings which could change how PCOS is diagnosed. Stay tuned… 👀
Breaking Down the Rotterdam Criteria
Remember: you need to meet 2 out of 3 criteria, AND other conditions must be ruled out.
Criterion #1: Oligo-ovulation or Anovulation
What it means: Irregular or absent ovulation, which typically shows up as irregular periods.
In practice:
Oligomenorrhea: Cycles longer than 35 days or fewer than 8-9 periods per year
Amenorrhea: No period for 3+ months (if you previously had regular cycles)
Cycles shorter than 21 days also count
How it’s assessed:
Your menstrual history
Progesterone blood tests (low levels mid-luteal phase suggest you didn’t ovulate)
Ovulation tracking (though this alone isn’t diagnostic)
Important note: If you’re on hormonal birth control, your periods are artificially regulated, so this criterion can’t be properly assessed. Many doctors will ask you to come off birth control for 3-6 months before diagnosis (if medically appropriate).
Criterion #2: Clinical or Biochemical Hyperandrogenism
What it means: Evidence of excess male hormones (androgens).
Clinical Hyperandrogenism (visible signs):
Hirsutism: Excess hair growth in male-pattern areas (face, chest, back, abdomen). Typically assessed using the Ferriman-Gallwey score - a standardised scoring system of hair growth in 9 body areas
Acne: Particularly severe, persistent, or adult-onset acne
Androgenic alopecia: Male-pattern hair loss or thinning at the crown
Important context: What counts as “excess” varies by ethnicity. Hair growth patterns differ significantly across populations, so assessment should be culturally sensitive.
Biochemical Hyperandrogenism (blood tests):
Elevated levels of:
Total testosterone
Free testosterone (often more sensitive)
Androstenedione
DHEA-S
The tricky part:
Androgen levels can be normal in some women with PCOS (hence why you only need 2/3 criteria)
Levels fluctuate throughout your cycle
Different labs use different reference ranges
Birth control suppresses androgens, masking results
Criterion #3: Polycystic Ovaries on Ultrasound or AMH levels
What it means: Your ovaries show a specific appearance on ultrasound. In adults, anti-Müllerian hormone (AMH) levels can be used instead of an ultrasound to identify polycystic ovaries.
2018 criteria define polycystic ovaries as:
20 or more follicles (small fluid-filled sacs) in at least one ovary, OR
Ovarian volume greater than 10 mL (in adults)
Because the Rotterdam criteria use a “2 out of 3” approach, women can have PCOS with different combinations of symptoms, creating four distinct phenotypes.
Critical misconceptions to clear up:
❌ These are NOT cysts – They’re follicles, which are normal structures. Every menstruating woman has follicles; in PCOS, you just have more of them arrested in development.
❌ You don’t need polycystic ovaries to have PCOS – Remember, it’s 2 out of 3 criteria. You can have PCOS with completely normal-looking ovaries if you meet the other two criteria.
❌ Having polycystic ovaries alone doesn’t mean you have PCOS – Up to 20-30% of women have polycystic-appearing ovaries on ultrasound but no other symptoms. This is called “polycystic ovarian morphology” and is considered a normal variant.
Technical note: Transvaginal ultrasound is more accurate than abdominal ultrasound for visualising ovarian morphology. The criteria I mentioned (20+ follicles) applies to transvaginal ultrasound. If you haven’t been sexually active, transabdominal or transrectal ultrasound may be used, though they’re less precise.
What Else Needs to Be Ruled Out?
PCOS is a diagnosis of exclusion, meaning your doctor must rule out other conditions that can look like PCOS:
Thyroid disorders (hypothyroidism can cause irregular periods)
Hyperprolactinemia (elevated prolactin can disrupt ovulation)
Non-classic congenital adrenal hyperplasia (genetic disorder affecting hormone production)
Cushing’s syndrome (excess cortisol)
Androgen-secreting tumours (rare but serious)
Pregnancy (obvious, but needs to be ruled out!)
Your doctor will typically order blood tests to check thyroid function (TSH, free T4), prolactin, and sometimes additional tests based on your symptoms.
What to Expect During the Diagnostic Process
Initial Visit:
Your doctor will take a detailed history:
Menstrual pattern history
Weight changes
Skin and hair symptoms
Family history of PCOS, diabetes, or infertility
Physical exam looking for clinical hyperandrogenism
Blood Work:
Comprehensive panel typically includes:
Reproductive hormones: LH, FSH, estradiol, testosterone (total and free), DHEA-S, androstenedione, AMH
Metabolic markers: Fasting glucose, fasting insulin, HbA1c, lipid panel
Thyroid function: TSH, free T4
Prolactin
Timing matters: Ideally, reproductive hormones are checked early in your cycle (days 2-5), but if your cycles are very irregular, timing may be less critical.
Pelvic Ultrasound:
Transvaginal ultrasound to assess:
Ovarian morphology (follicle count, ovarian volume)
Endometrial thickness
Rule out other pelvic pathology
Follow-up:
If initial findings are ambiguous, your doctor may:
Repeat blood work at different cycle phases
Ask you to track cycles for 3-6 months
Request additional testing
Moving Forward After Diagnosis
If you meet the Rotterdam criteria for PCOS, your doctor should:
Assess metabolic health: Screen for insulin resistance, prediabetes, or diabetes
Evaluate cardiovascular risk: Check blood pressure, lipid panel
Discuss symptom management: Address your specific concerns (acne, hair growth, irregular periods, fertility)
Create a monitoring plan: Regular screening for metabolic complications
Discuss lifestyle interventions: Diet, exercise, stress management, sleep
The Bottom Line
PCOS diagnosis using the Rotterdam criteria requires:
2 out of 3 features: irregular ovulation, hyperandrogenism, or polycystic ovaries
Exclusion of other conditions that can mimic PCOS
Comprehensive evaluation including history, physical exam, blood work, and imaging
The diagnosis isn’t always straightforward, and it may take time to gather all the necessary information.
If you suspect you have PCOS:
Find a doctor knowledgeable about PCOS (reproductive endocrinologist, gynecologist, or endocrinologist)
Keep detailed menstrual cycle records
Document your symptoms (photos can be helpful for tracking acne or hair growth)
Ask questions about which specific criteria you meet
Request copies of your test results
Don’t hesitate to seek a second opinion if something doesn’t feel right
Understanding the diagnostic criteria empowers you to be an informed advocate for your own health. PCOS is complex, but with proper diagnosis and management, women with PCOS live full, healthy lives 🩵