Polycystic ovary syndrome (PCOS) is the most common hormonal disorder in women of reproductive age. The name comes from the observation of small follicles (or "cysts") that often appear on the ovaries. However, not everyone with PCOS has these follicles, and they are not the cause of the condition.
PCOS is diagnosed when a person has at least two of the following three features: irregular menstrual periods, high testosterone or related symptoms (like excess facial hair), or polycystic ovaries found on an ultrasound. A blood test for high levels of anti-Müllerian hormone can replace the ultrasound in the diagnosis. Other symptoms associated with PCOS are heavy periods, acne, difficulty getting pregnant, and patches of darker skin.