Counting follicles to define polycystic ovary morphology: should we change the way we do it?

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Didier Dewailly, M.D.


Since the Rotterdam consensus in 2003, the ultrasound aspect of polycystic ovary morphology (PCOM) has been part of the diagnostic classification of polycystic ovary syndrome (PCOS), in association with at least 1 of the 2 items “oligo-anovulation” and “hyperandrogenism.” At the time, the official definition of PCOM was several follicles of 2–9 mm per ovary (FNPO) ≥12 or an ovarian volume (OV) ≥10 mL. Since then, this definition has evolved, mainly due to the improved performance of ultrasound equipment, which now offers images with much better resolution because of high-frequency endovaginal probes (≥8 MHz). This evolution exclusively concerns the FNPO, the measurement of OV not impacted by technical progress, but this parameter is much less sensitive than the FNPO, which remains the main measurement. With the improvement of follicle counting, the FNPO threshold ≥12 to define PCOM has become obsolete, and a recent international guideline recommends a threshold ≥20 with high-frequency endovaginal probes (≥8 MHz) (1).

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Fertility and Sterility

Editorial Office, American Society for Reproductive Medicine

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