In women with PCOS, the ovary doesn't make all of the hormones needed for any of the eggs to fully mature. However, no egg matures sufficiently to become dominant and thus ovulation does not occur.
Furthermore, the hormone progesterone is not produced.
When it matures, the follicle breaks open, releasing the egg to travel towards the fallopian tube – the process known as ovulation.
The remaining cells that surrounded the follicle secrete progesterone.
If that is not sufficient and the woman is not trying to get pregnant, hormonal contraception regimens can generate a more predictable cycle.
While this controls the symptoms, it does not cure PCOS and the menstrual cycle will become abnormal again if the pill is stopped.
Fortunately, it can generally be treated with medication to induce ovulation.