Polycystic ovaries contain a large number of harmless follicles that are up to 8mm (approximately 0.3in) in size.
The follicles are underdeveloped sacs in which eggs develop. In PCOS, these sacs are often unable to release an egg, which means ovulation does not take place.
It's difficult to know exactly how many women have PCOS, but it's thought to be very common, affecting about 1 in every 5 women in the UK.
More than half of these women do not have any symptoms.
Signs and symptoms
If you have signs and symptoms of PCOS, they'll usually become apparent during your late teens or early 20s.
They can include:
- irregular periods or no periods at all
- difficulty getting pregnant as a result of irregular ovulation or failure to ovulate
- excessive hair growth (hirsutism) – usually on the face, chest, back or buttocks
- weight gain
- thinning hair and hair loss from the head
- oily skin or acne
What causes PCOS?
The exact cause of PCOS is unknown, but it often runs in families.
It's related to abnormal hormone levels in the body, including high levels of insulin.
Insulin is a hormone that controls sugar levels in the body.
Many women with PCOS are resistant to the action of insulin in their body and produce higher levels of insulin to overcome this.
This contributes to the increased production and activity of hormones like testosterone.
Being overweight or obese also increases the amount of insulin your body produces.
There's no cure for PCOS, but the symptoms can be treated. Speak to a GP if you think you may have the condition.
Medications are also available to treat symptoms such as excessive hair growth, irregular periods and fertility problems.
If fertility medications are not effective, a simple surgical procedure called laparoscopic ovarian drilling (LOD) may be recommended.
This involves using heat or a laser to destroy the tissue in the ovaries that's producing androgens, such as testosterone.
With treatment, most women with PCOS are able to get pregnant.