Is a specific ovary size a determining factor for Polycystic Ovary Syndrome (PCOS)?

Ovary Size Criteria for PCOS Diagnosis

According to current international guidelines, an ovarian volume ≥10 ml on either ovary is one of the established ultrasound criteria for polycystic ovarian morphology (PCOM), which is a component of PCOS diagnosis, but ovary size alone is not sufficient to diagnose PCOS. 1, 2

Ultrasound Criteria for PCOM

The International Evidence-based Guideline for PCOS provides specific ultrasound criteria for identifying polycystic ovarian morphology:

• Ovarian Volume: ≥10 ml on either ovary 1
• Follicle Count: ≥20 follicles (2-9 mm in diameter) per ovary using endovaginal ultrasound with 8MHz transducer 1

Either criterion (ovarian volume or follicle count) is sufficient to establish PCOM on ultrasound 1.

Important Diagnostic Considerations

1. PCOM is only one component of PCOS diagnosis:

   • PCOS diagnosis requires two of three Rotterdam criteria:
     • Oligo/anovulation
     • Clinical/biochemical hyperandrogenism
     • Polycystic ovarian morphology on ultrasound 2

2. Technical specifications matter:

   • Transvaginal ultrasound is preferred for accurate assessment 1
   • For transabdominal ultrasound, only ovarian volume (≥10 ml) should be used due to difficulty in reliably assessing follicle count 1
   • Ultrasound should be performed when ovaries are quiescent (no dominant follicles, corpus luteum, or cysts) 1

3. Age-specific considerations:

   • Ultrasound should not be used for PCOS diagnosis in those with gynecological age <8 years (less than 8 years after menarche) due to high incidence of multi-follicular ovaries in this life stage 1, 2

Diagnostic Accuracy of Ultrasound Markers

Recent evidence from a diagnostic meta-analysis indicates:

• Follicle number per ovary (FNPO) is the most accurate diagnostic marker (sensitivity: 84%, specificity: 91%, AUC: 0.905) 1
• Ovarian volume has good but slightly lower diagnostic accuracy (sensitivity: 81%, specificity: 81%, AUC: 0.856) 1

Common Pitfalls to Avoid

1. Relying solely on ovary size: PCOS diagnosis requires more than just ovarian morphology 2

2. Using ultrasound in adolescents: Avoid using ultrasound criteria in young adolescents (<8 years post-menarche) as multi-follicular ovaries are common in this age group 1, 2

3. Ignoring technology limitations: Older ultrasound technology may not accurately visualize follicles, making ovarian volume (≥10 ml) the more reliable criterion in these cases 1

4. Failing to exclude other disorders: Other conditions that can cause similar presentations must be ruled out before confirming PCOS diagnosis 2

5. Misinterpreting normal variations: Geographic differences in diagnostic accuracy exist, potentially due to variations in age, BMI, and diagnostic criteria 1

By following these evidence-based criteria and avoiding common pitfalls, clinicians can more accurately use ovarian size as one component in the comprehensive evaluation of potential PCOS.