What is considered an enlarged ovarian volume in patients with Polycystic Ovary Syndrome (PCOS)?

Enlarged Ovarian Volume in PCOS

According to international evidence-based guidelines, an ovarian volume ≥10ml in either ovary is considered enlarged and diagnostic of polycystic ovarian morphology (PCOM) in patients with PCOS. 1

Diagnostic Criteria for Ovarian Volume in PCOS

The International Evidence-based Guideline for PCOS provides clear criteria for ovarian volume assessment:

• Using endovaginal ultrasound transducers with a frequency bandwidth that includes 8MHz, an ovarian volume ≥10ml on either ovary is considered enlarged 1
• This threshold applies regardless of whether using newer or older ultrasound technology 1
• The finding must be present in at least one ovary to be considered diagnostic 2
• Measurements should be taken when no corpus luteum, cysts, or dominant follicles (≥10mm) are present 1

Technical Considerations for Accurate Assessment

When measuring ovarian volume, several technical factors should be considered:

• Transvaginal ultrasound is the preferred approach for accurate ovarian volume assessment if sexually active and acceptable to the patient 1
• For transabdominal ultrasound, which may be less reliable for follicle counting, focus primarily on ovarian volume measurement 1
• Three-dimensional measurements of the ovary should be taken to calculate volume 1
• If a follicle >10mm is present, the scan should be repeated at a time of ovarian quiescence 2

Clinical Context and Interpretation

The significance of enlarged ovarian volume must be interpreted within the broader clinical context:

• Ovarian volume should be assessed alongside other diagnostic criteria for PCOS, including clinical/biochemical hyperandrogenism and ovulatory dysfunction 1, 3
• In patients with irregular menstrual cycles and hyperandrogenism, ultrasound is not necessary for PCOS diagnosis, though it helps identify the complete phenotype 1
• 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

Alternative Diagnostic Approaches

While ovarian volume is important, other parameters may be considered:

• Follicle number per ovary (FNPO) ≥20 is an alternative criterion for PCOM using high-resolution ultrasound 1, 4
• More recent recommendations suggest increasing the FNPO threshold to ≥25 follicles when using newer high-resolution technology (transducer frequency ≥8 MHz) 4
• Serum AMH shows promise as a surrogate marker for PCOM but is not yet recommended as a substitute for ultrasound assessment 1

Common Pitfalls and Caveats

Several important considerations should be kept in mind:

• Not all PCOS patients have enlarged ovaries; studies have shown that up to 29% of confirmed PCOS cases had normal ovarian volume 5
• Ovarian volume has less diagnostic potential for PCOM compared with follicle number per ovary 4
• The presence of PCOM alone (without hyperandrogenism or ovulatory dysfunction) is not sufficient for PCOS diagnosis 1, 2
• Age-specific cut-off values for PCOM should be considered, as ovarian volume and follicle counts decrease with age 1

The threshold of ≥10ml for ovarian volume has remained consistent in guidelines since 2003 2, despite updates to follicle count thresholds, indicating its reliability as a diagnostic marker for PCOM in PCOS.