What are the diagnostic criteria for polycystic ovary syndrome (PCOS) using the Rotterdam criteria?

Diagnosing Polycystic Ovary Syndrome (PCOS)

Use the Rotterdam criteria to diagnose PCOS: the patient must have at least 2 of 3 features—oligo/anovulation, clinical or biochemical hyperandrogenism, and polycystic ovarian morphology on ultrasound—after excluding other conditions that mimic PCOS. 1, 2, 3

Core Diagnostic Criteria

The Rotterdam criteria remain the international standard for PCOS diagnosis in adults, requiring any 2 of the following 3 features 1, 2, 3:

• Oligo/anovulation: Menstrual cycles >35 days, amenorrhea, or fewer than 8 cycles per year 1
• Hyperandrogenism: Clinical signs (hirsutism, acne, male-pattern balding, clitoromegaly) or biochemical elevation of androgens 1, 2
• Polycystic ovarian morphology: Specific ultrasound findings detailed below 1, 3

Critical caveat: You must exclude other conditions before confirming PCOS, including thyroid disease, hyperprolactinemia, non-classic congenital adrenal hyperplasia, Cushing's syndrome, and androgen-secreting tumors 1, 2.

Ultrasound Diagnostic Thresholds

Follicle number per ovary (FNPO) ≥20 follicles (2-9mm diameter) is the gold standard ultrasonographic marker, with 87.64% sensitivity and 93.74% specificity. 4, 1, 5

When accurate follicle counting is not possible 4, 1:

• Alternative marker: Ovarian volume >10 mL in at least one ovary 4, 1, 6
• Secondary alternative: Follicle number per single cross-section (FNPS) 4, 1

Technical requirements for optimal imaging 1, 7:

• Use transvaginal ultrasound with ≥8 MHz transducer frequency in adults
• Document three dimensions and volume of each ovary
• Ensure no corpora lutea, cysts, or dominant follicles ≥10mm are present
• Count total follicles per ovary measuring 2-9mm

Biochemical Hyperandrogenism Testing

Total testosterone measured by liquid chromatography-tandem mass spectrometry (LC-MS/MS) is the single best initial biochemical marker, with 74% sensitivity and 86% specificity. 1, 2

Additional androgen markers in order of diagnostic utility 1:

• Calculated free testosterone (using Vermeulen equation): 89% sensitivity, 83% specificity—highest sensitivity of all markers
• Free androgen index (FAI): 78% sensitivity, 85% specificity (caution when SHBG <30 nmol/L)
• Androstenedione: 75% sensitivity, 71% specificity (useful when SHBG is low)
• DHEAS: 75% sensitivity, 67% specificity (most reliable for adrenal androgen production, particularly in women <30 years)

Important: All biochemical testing must be performed in the absence of hormonal contraception, as progestin-containing methods suppress the hypothalamic-pituitary-ovarian axis and make hormone levels unreliable 1.

Age-Specific Diagnostic Modifications

Adolescents (<20 years or <8 years post-menarche)

Do not use ultrasound as a diagnostic tool in adolescents due to poor specificity and high false-positive rates from normal multifollicular ovaries. 1, 7, 8, 3

For adolescent diagnosis 8, 3:

• Require BOTH hyperandrogenism AND irregular cycles (not just 2 of 3 Rotterdam criteria)
• Wait at least 2-3 years post-menarche before diagnosing, as irregular cycles are physiologic in 75% of early post-menarchal adolescents 8
• Polycystic ovarian morphology appears in up to 40% of adolescents 2 years post-menarche and is not predictive of future abnormalities 8

Adults (≥18 years, ≥8 years post-menarche)

Full Rotterdam criteria apply with transvaginal ultrasound appropriate and recommended 1, 3.

Anti-Müllerian Hormone (AMH) Considerations

AMH should NOT be used for clinical diagnosis of PCOS due to lack of standardization, no validated cut-offs, and significant overlap between women with and without PCOS. 1, 5

While AMH levels are 2-3 times higher in women with PCOS compared to controls 5, critical limitations prevent clinical adoption 5:

• Inconsistent cut-off values ranging from 24.29 to 100 pmol/L across studies
• Substantial assay variability and discrepancies in between-assay conversion factors
• Age-dependent variability requiring age-specific reference ranges that don't exist
• Significant overlap with normal women, particularly in younger age groups

Exception: AMH may be useful in adolescents within 8 years of menarche where ultrasound is contraindicated, but this remains investigational 5.

Mandatory Exclusion of Other Diagnoses

Before confirming PCOS, systematically exclude 1, 2:

• Cushing's syndrome: Look for buffalo hump, moon facies, hypertension, abdominal striae
• Androgen-secreting tumors: Rapid onset and severe hyperandrogenism warrant immediate evaluation
• Non-classic congenital adrenal hyperplasia: Check 17-hydroxyprogesterone
• Thyroid disease: TSH measurement
• Hyperprolactinemia: Prolactin level
• Primary hypothalamic amenorrhea or primary ovarian failure: FSH, LH assessment
• Acromegaly: If clinical suspicion exists

Required Metabolic Screening After Diagnosis

All women with PCOS must be screened for metabolic complications regardless of BMI, as insulin resistance occurs independently of body weight. 1, 2

Mandatory screening includes 1, 6, 2:

• Two-hour oral glucose tolerance test (especially if BMI >30 kg/m²)
• Fasting lipid profile (triglycerides, HDL cholesterol)
• BMI and waist-hip ratio calculation
• Blood pressure measurement
• Cardiovascular risk factor assessment

Common Diagnostic Pitfalls to Avoid

Up to one-third of reproductive-aged women without PCOS have polycystic ovarian morphology on ultrasound—ultrasound findings alone are insufficient for diagnosis. 1

Additional pitfalls 1, 7:

• Transient multifollicular appearance can occur after discontinuing birth control and does not represent true PCOS
• Excessive exercise (e.g., twice daily, 6 days/week) can cause hypothalamic suppression and amenorrhea mimicking PCOS
• IUDs do not interfere with ovarian imaging as they sit within the endometrial cavity while ovaries are separate lateral structures 7
• Ovarian volume <3 cm³ with <5 antral follicles suggests diminished ovarian reserve, not PCOS, and requires different workup 1

Practical Diagnostic Algorithm

1. Document clinical history 1:

   • Menstrual cycle pattern (cycle length >35 days suggests chronic anovulation)
   • Signs of androgen excess (acne, hirsutism, balding, onset and duration)
   • Medication use (including exogenous androgens, hormonal contraception)
   • Family history of cardiovascular disease and diabetes
   • Lifestyle factors (diet, exercise, alcohol, smoking)

2. Perform physical examination 1:

   • Calculate BMI and waist-hip ratio
   • Assess for hyperandrogenism signs (acne, balding, hirsutism, clitoromegaly)
   • Measure blood pressure

3. Order biochemical testing 1:

   • Total testosterone via LC-MS/MS (first-line)
   • Calculated free testosterone using Vermeulen equation
   • Consider androstenedione, DHEAS, FAI based on initial results
   • TSH, prolactin to exclude mimicking conditions
   • 17-hydroxyprogesterone if non-classic CAH suspected

4. Obtain transvaginal ultrasound (if ≥8 years post-menarche) 1, 7:

   • Count follicles 2-9mm per ovary (goal: FNPO ≥20)
   • Measure ovarian volume (alternative threshold: >10 mL)
   • Use ≥8 MHz transducer frequency

5. Apply Rotterdam criteria: Confirm at least 2 of 3 features present after exclusions 1, 2, 3

6. Complete metabolic screening: OGTT, fasting lipids, cardiovascular risk assessment 1, 6, 2