(PCO) The full name (almost never used) is micro-polycystic ovaries: it's a diagnosis best made on transvaginal ultrasound, with lots of medium-sized follicles visible around the rim of the ovaries; can be part of the polycystic ovary syndrome. (The 'cysts' are not real cysts. Think of them as stalled follicles. They don't need to be treated.) A very common condition: about 20% of women have it, though only a few women have the full syndrome.

Early experience with superovulation for in vitro fertilisation, particularly at the original US program in Norfolk VA, saw women patients classified into three classes of responders, depending on how many eggs were obtained at egg retrieval. Poorer than usual outcomes could occur with either a low response or a high response (the high responders generally have polycystic ovaries, with a risk of ovarian hyperstimulation syndrome (OHSS). Many maneuvers have been used to try and retrieve more eggs among low responders, such as starting high dose FSH on day 1, the adding of growth hormone, the avoidance of GnRH-agonists etc., all generally without improving the results. Day 3 serum FSH levels can be high in low responders, indicating a depletion of eggs in the ovaries.

(PCOS) A syndrome that consists of polycystic ovaries associated with any clinical symptom or sign of too much male hormone effect, such as acne, excess body hair (hirsutism), or long or absent cycles (oligomenorrhea or amenorrhea). Often called polycystic ovarian disease in the US (PCOD).