Important: This is intended as general information only. It may not apply to your specific situation.  It is not a substitute for medical advice.  If you have a question or concern, please raise it with me at your next appointment or contact me sooner if it's urgent.

Polycystic Ovarian Syndrome - What is Polycystic Ovarian Syndrome?

Polycystic Ovarian Syndrome (PCOS) is a big topic so I’ve divided it into two sections.  In this section we will look at what happens in your body when you have PCOS and the symptoms it produces.  See the Treating PCOS information page for treatment options.

Polycystic ovarian syndrome is a common disorder of women which is due to a hormone imbalance.  In women with PCOS we see an imbalance in the amount of androgens (often called ‘male’ hormones although they are present in smaller amounts in normal women) and oestrogens circulating in the body.  This has many effects throughout the body and different women experience different symptoms.  To be diagnosed with PCOS you must have at least two of the following

  • Irregular periods
  • Signs of hyperandrogenism (more about this later)
  • Polycystic ovaries on ultrasound (the appearance of multiple small cysts on the ovaries)

Polycystic Appearing Ovaries

The term ‘polycystic appearing ovaries’ refers to the ultrasound appearance of multiple small cysts on the ovaries.  PCOS is not the only thing that can cause this appearance.  We also see polycystic appearing ovaries in some other conditions and in some completely normal women. Therefore, having the ultrasound appearance alone is not enough to make the diagnosis.  Just to confuse things further, not all women who have PCOS have the typical polycystic appearing ovaries on ultrasound.


The term ‘hyperandrogenism’ means higher than normal blood levels of the androgen group of hormones.  These include testosterone, androstenedione and  dehydroepiandrosterone.  Although these are sometimes called ‘male’ hormones (particularly testosterone), normal women have these hormones present in their blood streams at low levels. 

Hyperandrogenism may cause excessive hair growth in various places including the face, chest, lower abdomen and thighs.  It may also cause oily skin and acne.

The diagnosis of hyperandrogenism can be made clinically (that is, by observing excess hair growth, oily skin and acne) or biochemically (that is, by doing a blood test and seeing that the levels are higher than normal).

Symptoms of PCOS

Women with PCOS may have some, or all, of the following

  • Irregular periods
  • Difficulty falling pregnant
  • Acne
  • Abnormal hair growth
  • Hair loss from the scalp
  • Weight gain or obesity

Cause of PCOS

This is a bit controversial.  There does not seem to be one single cause of PCOS in all women.  PCOS can run in families and it appears that there are genetic factors  at work.  However, there is almost certainly more than one gene involved and, in fact, different combinations of genes in different women.  These genes interact with various environmental factors.

A central factor in PCOS seems to be a problem with the way your body handles the hormone insulin.  Many women with PCOS are less sensitive to the actions of insulin.  This is known as insulin resistance.  The body can compensate for this (to a degree) by producing more insulin resulting in higher insulin levels.  Increased insulin levels affect the ovaries resulting in an imbalance in the hormones produced.  Insulin resistance can be genetic but there are probably many different genes that can cause it.  Gaining weight also causes insulin resistance.

Weight and PCOS

The interplay between PCOS and weight is complex.  It is quite common for women with PCOS to be overweight or obese.  However, many women with PCOS are of normal weight or even slim.   

We know that when people’s weight increases, their insulin resistance also increases.  Therefore, if you are genetically a bit insulin resistant, an increase in your weight might be enough to increase your insulin resistance to the point that you develop PCOS.  For this reason, we advise overweight women who have PCOS to lose weight.  In these women, we are hoping that weight loss will cause them to be more sensitive to insulin, allowing their insulin levels to fall and their hormone imbalance to correct itself.

But what about normal or even skinny women with PCOS?  Presumably, these women are genetically more insulin resistant so that they have higher than normal insulin levels even at normal weights.  There’s not much you can do about your genes.  Women of normal weight should not be encouraged to lose weight as being underweight causes its own problems.  Having said this, a healthy lifestyle and regular exercise is as important for these women as it is for everyone else.

The Menstrual Cycle and PCOS

To understand the effect PCOS has on your menstrual cycle, you first need to understand how a normal menstrual cycle works.  In a normal menstrual cycle, your body spends the first half of the cycle (approximately two weeks) growing an egg.  The egg develops in a small cyst called a follicle, which grows to about 2cm in diamteter.  The cells surrounding the cyst produce oestrogen and this causes the lining of the uterus to grow.  At approximately the middle of the cycle, the egg bursts out of the follicle – this is known as ovulation.  After ovulation, the cells left behind in the follicle change and become something known as a corpus luteum.  The corpus luteum produces progesterone which, among other things, stabilizes the lining of the uterus.  If you don’t fall pregnant, the corpus luteum dies after about 14 days causing the progesterone level to drop.  This falling progesterone level is what causes you to have a period. 

So, in summary: in a normal menstrual cycle you produce oestrogen and grow a follicle in the first two weeks of the cycle, ovulate in the middle of the cycle and produce progesterone (as well as continuing to produce oestrogen) in the second two weeks of the cycle.

In PCOS, the follicles and eggs don’t develop properly.  Your body tries to make follicles but because of the hormone imbalance present in your body, it often can’t quite get there.  The multiple small cysts seen on the ovaries during ultrasounds are follicles that got ‘stuck’ at an early stage of development because of the hormone imbalance.  Because the follicles don’t develop and ovulate each month, you may not have regular periods and it can be difficult to get pregnant. 

Remember that every case of PCOS is different.  Some women ovulate regularly and have regular periods.  Many others ovulate every now and then and have irregular periods.  This means that, while it can be hard for women with PCOS to get pregnant, it is possible.  Many women with PCOS need help to get pregnant.  However, you can’t rely on the fact that you have PCOS to protect you from an unwanted pregnancy – you may ovulate and get pregnant when you least expect it.

Other effects of PCOS

The basic problem of PCOS – the insulin resistance and hormone imbalance – has other effects throughout the body.  Over the course of their lives, women with PCOS are at increased risk of high blood pressure and high cholesterol which can, if untreated, result in heart attacks and strokes.  They are also at risk of type II diabetes. 

Women who don’t ovulate for long periods of time are also at increased risk of cancer of the lining of the uterus (endometrial carcinoma).  This is because, instead of balance between oesterogen and progesterone seen in normal ovulatory cycles, these women produce oestrogen only.  Oestrogen causes the lining of the uterus to grow while progesterone stabilizes it, or ‘calms it down’.   Without ovulation, the lining of the uterus is stimulated to grow by oestrogen but doesn’t get the balancing ‘calming’ effect of progesterone.  Over many years this can increase the risk of the lining of the uterus developing cancer.

There are steps we can take to reduce all these risks, which we will talk about on the Treating PCOS information page.

Diagnosing PCOS

A diagnosis of PCOS is made on the basis of your symptoms, hormone levels and ultrasound findings.  It is also important to test some other hormone levels to make sure that you don’t have another hormone problem masquerading as PCOS.