Blood samples from women with Polycystic Ovarian Syndrome show that gonadotrophin secretion is disordered resulting in increased plasma LH relative to FSH levels. FSH peaks, which characterise ovulatory cycles, are absent and therefore pro-ovulatory follicular development ceases. Thus the granulosa cells do not acquire a fully activated aromatase system and remain unresponsive to LH. Because of this, healthy follicles in polycystic ovaries rarely develop beyond 5mm. Oestrogens are normally converted from androgens in the presence of aromatase which is decreased when high levels of: H exists. In women with Polycystic Ovarian Syndrome therefore, oestrogen synthesis and production of oestradiol from granulosa cells is decreased and atresia of the follicle occurs. This atresia causes a build up of secondary interstitial tissue and ovarian stroma. This disorder of gonadotrophin secretion causes anovulation.

Women with Polycystic Ovarian Syndrome have elevated plasma androgen levels i.e. raised serum concentration of testosterone, and this may represent the most sensitive single biochemical marker of Polycystic Ovarian Syndrome. These increased androgens are secondary to pulsatile release of LH by the pituitary and cause hirsutism and can be associated with acne and oily skin.

Assessment of serum levels of progesterone on day 21 of the menstrual cycle will deternine whether ovulation has occurred by detecting high levels of progesterone which is secreted by the corpus luteum. Other blood tests may be performed to exclude other causes of hyperandrogenism, such as Cushing