Causes of PCOS

Polycystic Ovary Syndrome: What causes PCOS?

Although first described over 65 years ago, we still do not know the exact cause of PCOS. Theories regarding the mechanism(s) include the effects of abnormal pituitary hormone secretion, high levels of insulin, and abnormal production of male hormones by the ovary.

The pituitary gland secretes two hormones, luteinizing hormone (LH) and follicle-stimulating hormone (FSH). In general, LH controls the production of female hormones (estrogen and progesterone) in the ovary and FSH controls the development and release of eggs in the ovary. LH and FSH are released in pulses from the pituitary gland in response to stimulation by gonadotropin releasing hormone (GnRH) from the brain. LH and FSH secretion normally varies throughout the menstrual cycle, and it appears that different patterns of GnRH pulses from the brain affect the different patterns of LH and FSH secretion. Specifically, fast GnRH pulses appear to favor LH secretion, and slow GnRH pulses favor FSH secretion. Estrogen and progesterone from the ovary regulate how frequently the brain secretes GnRH pulses, and also the amount of GnRH secreted per pulse.

A key point is that the pulses of GnRH are slowed by the elevated levels of estrogen and progesterone that normally occur after ovulation. Studies suggest that this slowing of GnRH allows for later FSH secretion (at the time of menstruation), which normally leads to egg development in the next cycle. These same studies would suggest that if GnRH pulses are not slowed down, subsequent FSH production is diminished. One can therefore see that this ability to slow GnRH pulses seems to be quite important for subsequent FSH secretion, and therefore subsequent development of an egg.

Studies have shown that GnRH secretion in patients with PCOS is relatively fast, and that it does not slow down very well in response to estrogen and progesterone. We believe that this helps to explain why PCOS patients frequently do not ovulate. Women with PCOS often have high levels of LH secretion. High levels of LH contribute to the high levels of androgens (male hormones such as testosterone), and this along with low levels of FSH contributes to poor egg development and an inability to ovulate. A lack of ovulation also leads to relative deficiencies of progesterone production by the ovary, which often leads to absence of menstrual periods.