Polycystic ovary syndrome

Diagnostic criteria (Polycystic Ovarian Morphology - PCOM)

Diagnosis requires one of the following findings in either ovary (exclusion of corpus luteum, cysts, or dominant follicles required):

• Follicle Number per Ovary (FNPO): $\ge$ 20 follicles measuring 2–9 mm in diameter.
  • Note: This threshold applies when using high-frequency transvaginal transducers ($\ge$ 8 MHz). If older technology is used, the follicle count is unreliable, and ovarian volume should be used instead.
• Ovarian Volume: > 10 ml.
  • Formula: $Length\times Width\times Height\times 0.5$ (or $0.523$).
  • This is often considered the most reliable metric if image quality prevents accurate follicle counting.

Guideline evolution (The "12 vs 20" Trap)

• Rotterdam Criteria (2003): Originally defined PCOM as $\ge$ 12 follicles or volume > 10 ml.
• 2018/2023 Guidelines: Raised the threshold to $\ge$ 20 follicles due to improvements in ultrasound resolution.
• Exam strategy: If an exam question stems from older literature, '12 follicles' may still be the intended answer. However, for current practice and modern boards, $\ge$ 20 is the evidence-based standard.

Exclusion criteria

• If a dominant follicle (> 10 mm) or corpus luteum is present, the scan should be repeated during the early follicular phase (Days 2–5) to accurately assess volume and FNPO.
• Adolescents: Pelvic ultrasound is not recommended for the diagnosis of PCOS in patients < 8 years post-menarche due to the high physiological prevalence of multi-follicular ovaries.

Differential diagnosis

• Multi-follicular Ovaries (MFO):
  Often seen in puberty or hypothalamic amenorrhea. Typically have normal ovarian volume and roughly 6–10 follicles scattered throughout the stroma (not strictly peripheral).