Causes

The exact cause of polycystic ovary syndrome (PCOS) is unknown, but it's thought to be related to abnormal hormone levels.

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 from bloodinto cells, where it's broken down to produce energy.

Insulin resistance meansthe 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, which interferes with the development of the follicles (the sacs in the ovaries where eggs develop) and prevents normal ovulation.

Insulin resistance can also lead to weight gain, which can make PCOS symptoms worse, because having excess fat causes thebody to produce even more insulin.

Hormone imbalance

Many women with PCOS are found to have an imbalance in certain hormones, including:

• raised levels of testosteronea hormone oftenthought of asa male hormone, although all women usually produce small amounts of it
• raised levels of luteinising hormone (LH)this stimulates ovulation, but mayhave an abnormal effect on the ovaries if levels are too high
• low levels of sex hormone-binding globulin (SHBG)a protein in the blood, which binds to testosterone and reduces the effect of testosterone
• raised levels of prolactin (only in some women with PCOS) hormone that stimulates the breast glands to produce milk in pregnancy

Theexactreasonwhythese hormonal changes occurisn't known. It's been suggested that the problem may start in the ovary itself, inother glands that produce these hormones, orin the part of the brain that controls their production.The changesmay also be caused by the resistance to insulin.

Genetics

PCOS sometimes runs in families. If any relatives, such as your mother, sister or aunt, have PCOS, then the risk of youdeveloping it is often increased.

This suggests there may be a genetic link to PCOS, although specific genesassociated with the condition haven't yet been identified.