20-30% of the female population have ovarian cysts. They are very common and usually harmless. Ovarian cysts are not the same thing as polycystic ovaries. You can read more about the differences here.
Polycystic ovaries are usually diagnosed using pelvic ultrasound scans. The highest quality data is obtained through transvaginal scans, however, not all women are comfortable with this, so scans can be performed via abdominal ultrasound instead. Discovering that you have polycystic ovaries does not mean that you have PCOS. However, if you have 12 or more follicles in each ovary measuring 2–9 mm in diameter, and/or an increased ovarian volume (10 mL or more), PCOS might be considered and your doctor may wish to test you against the other diagnostic criteria.