The exact cause of polycystic ovary syndrome (PCOS) is unknown, but the following factors often lead to its development.
Resistance to insulin
Insulin is a hormone produced by the pancreas to control the amount of sugar in the blood. It helps to move glucose out of the blood and into cells, where it is broken down to produce energy.
Insulin resistance means that the body's tissues are resistant to the effects of insulin. The body therefore has to produce extra insulin to compensate.
High levels of insulin cause the ovaries to produce too much testosterone (see below), which interferes with the development of the follicles and prevents normal ovulation.
Weight gain
Insulin resistance often makes it more difficult to lose weight, as raised insulin levels can lead to weight gain. Being overweight or obese makes the symptoms of PCOS more pronounced because excess fat causes the body to produce more insulin.
Hormone imbalance
Many women with PCOS are found to have an imbalance in certain hormones:
- Raised levels of testosterone and other male sex hormones results in many of the symptoms of PCOS (all women produce testosterone, but normally in much lower levels than men).
- Low levels of sex hormone binding globulin (SHBG), which means that testosterone levels are more active.
- Raised levels of luteinising hormone (LH), which is created in the pituitary gland to stimulate ovulation and hormone production in the ovaries. This excess is thought to have an abnormal effect on the ovaries.
- Raised levels of prolactin (only in some women with PCOS). This hormone usually stimulates the breast glands to produce milk in pregnancy.
The exact reason how and why this happens is not known. It's been suggested that the problem may start in the ovary itself, in the pituitary gland and part of the brain that controls it. Or it may be caused by the resistance to insulin.
Genetics
Polycystic ovary syndrome (PCOS) can sometimes run in families. If any of your relatives, such as your mother, sister or aunt, have PCOS then the risk of you developing it is often increased.
