How are PCO and PCOS diagnosed?

The “cysts” in PCO are actually small immature follicles, which, as explained above, are normal features of all ovaries; when large numbers of antral follicles are visible on ultrasound scan (>20 in the most recent guidelines released in 2018) and/or the volume of the ovary is increased, the ovary is considered to be polycystic.

For a diagnosis of PCOS, two out of three of the following criteria need to be present:

  1. Polycystic appearing ovaries (PCO) on ultrasound.
  2. Irregular, infrequent or absent periods, which reflect infrequent or absent ovulation (ovulation is the release of an egg from the ovary).
  3. Increased levels of male hormones or signs of increased male hormone effects, such as excessive body hair growth.