What really happens in PCOS?

In order to understand what happens in the polycystic ovary syndrome, it is important to understand a little about how a woman’s reproductive cycle functions.

Every woman knows that her eggs develop in her ovaries. Egg development is controlled by two hormones produced by the pituitary gland: follicle stimulating hormone, FSH, and luteinising hormone, LH.
The pituitary gland is the size of a peanut and is situated behind the eyes. It is connected to the base of the brain by a stalk. In the base of the brain just above the pituitary gland there is a centre than controls the production of FSH and LH in the pituitary gland. This is the brain’s fertility centre. In men, this centre works in a continuous fashion but in women, this centre works in a cyclic fashion, usually in a monthly cycle and, hence, we will refer to it as the fertility clock.

If the fertility clock is exposed to higher than average levels of male hormones in a woman, the clock begins to work in a continuous fashion like a man rather than in a monthly cyclic fashion, making ovulation unlikely.
The ovulation cycle can be turned off by high levels of a pituitary hormone prolactin, sometimes caused by stress and sometimes made excessively by a tumour of the pituitary gland secreting prolactin. This is an uncommon cause of the polycystic ovary syndrome.

Early in a woman’s cycle the fertility clock stimulates the pituitary gland to secrete a large amount of follicle stimulating hormone (FSH). FSH stimulates growth of the egg and the cells lining the follicle, the tiny bubble that holds the egg, so that the follicle enlarges and moves out towards the surface of the ovaries. At this stage, the follicle does not respond to stimulation by luteinising hormones (LH).

Around days 10, 11 or 12 of the cycle, the fertility clock stimulates the pituitary gland to make a very large amount of LH. By this time the follicle has become sensitive to LH stimulation. The surge in LH from the pituitary gland always stimulates the final step of maturation of the follicle after which no further growth is possible. At this stage the follicle and egg are ripe or mature and the follicle will rupture or ovulate, releasing the egg.

If ovulation does not occur, the follicle continues to produce oestrogen for some time, causing the lining of the womb to grow thicker than usual. The situation is made worse because the ovary does not produce progesterone if ovulation has not occurred. The lining of the womb then breaks away in an erratic fashion. This causes the menstrual bleeding to be long, often with large quantities of blood and tissue, causing menstruation that can be heavy, painful and prolonged.

The other obvious consequence of lack of ovulation is reduced fertility.
The long term effects  of this hormonal disturbance are many, and are discussed in another section (Why seek help?)