PCO vs PCOS: What’s The Difference and Which Do You Have?

Women often confuse Polycystic Ovaries (PCO) and Polycystic Ovarian Syndrome (PCOS) because they share a similar name and symptoms. But having polycystic ovaries does not always mean a woman has PCOS.

So despite their similarities, there are key differences between the two.

In this post, you will learn about both PCO and PCOS. We will first look at what PCO and PCOS are, as well as their symptoms and causes. Then we will talk through the tests Doctors use to diagnose both PCO and PCOS. Ultimately, you will discover the difference between the two and which you may have.

So, let's get started.

What’s the Difference Between PCO and PCOS?

As discussed, while PCO and PCOS may share a similar name, there are however, key differences. In this section, I am going to be identifying exactly what they are. So pay close attention.

What are Polycystic Ovaries (PCO)?

Now, despite the name these are not actually cysts the way you may think of them, but many small follicles. All female ovaries have follicles, these are the sacs that contain the immature eggs.

Normally, these eggs mature and then one egg is released during ovulation. But sometimes women do not ovulate and the follicle does not break to release the egg. As a result, follicles stay in the ovary and the ovaries appear to contain many ‘cysts’. If at least one ovary has 12 or more small ‘cysts’ (2–8 mm) the woman is said to have PCO.

What is PCOS?

Polycystic ovarian syndrome (PCOS) is a complex metabolic and hormonal condition that affects 10-20% of reproductive-age women. Women with PCOS produce too many male hormones, but can also have an imbalance of estrogen and progesterone.

Doctors use the Rotterdam Criteria to diagnose PCOS. Women must show two out of the three signs.

1) High androgens - your body produces high levels of male hormones. You may show signs of this physically, growing excess body or facial hair.

2) An irregular menstrual cycle -  The average menstrual cycle is between 21 to 35 days (on average 28 days). A cycle is irregular if it lasts longer than 35 days or less than 21 days. A missed period would also be an irregular cycle.

3) Polycystic Ovaries - Again, despite the name these are not actually cysts. Because women with PCOS suffer from a hormonal imbalance, they tend to not ovulate. As a result, follicles stay in the ovary and the ovaries appear to contain many ‘cysts’. As discussed, for an ovary to be polycystic, it must contain at least 12 of these 'cysts'.

But, as you can see, despite the name 'Polycystic Ovary Syndrome’, you don’t necessarily need to have polycystic ovaries to be diagnosed with PCOS.

In a Nutshell

While PCO and PCOS women both have multiple ‘cysts’ on their ovaries. There is a clear distinction between them. Women with PCOS often suffer from high male hormones, whilst women with PCO do not.

So, now you know what PCO and PCOS are. Let’s talk about how you can tell the difference between them based on your symptoms.


The Differences Between PCO and PCOS Symptoms

Women with PCO do not experience many symptoms, but the symptoms they do have are similar to PCOS. The symptoms PCO and PCOS have in common include polycystic ovaries, irregular or no periods at all, a lack of ovulation and infertility.

PCOS, however, not only impacts a woman’s reproductive functions, it can also affect her appearance. Women with PCOS can experience acne, hair loss, excess hair growth and weight gain. All because of the increased levels of male hormones they experience. Keep in mind, you do not need to experience all symptoms to be diagnosed with PCOS.

Now, you might be asking yourself.

If I have PCO or PCOS am I infertile?

So here’s the thing.

PCO and PCOS may impact your menstrual cycle and as a result your fertility. However, having PCO or PCOS does not make you infertile forever, it is often temporary. Once you rebalance your hormones, your cycles become regular and you can become fertile once again.

Causes of PCO

High anti-Müllerian hormone (AMH) Levels

As discussed, female ovaries contain follicles, the sacs that contain the immature eggs. Now, these follicles secrete AMH.

AMH in a Normal Ovary

AMH is released to ensure follicles grow at a slow rate to prevent premature development. It does this by reducing the sensitivity of the ovary receptors to follicle-stimulating hormone (FSH). FSH is released by the pituitary gland and its job is to stimulate the growth of follicles.

AMH in the Ovaries of PCO Women

Researchers have found that AMH levels in women with PCO higher than in non-PCO. So the follicles in women with PCO are producing high levels of AMH.

As a result, follicles cannot develop into a dominant egg, so this leads to a build-up of small follicles in the ovary. This is what causes a polycystic ovary.

Lack of Ovulation

Sometimes women just do not ovulate, so an egg is not released. As a result, follicles accumulate in the ovary. Now, there are various possible reasons for why ovulation does not happen including


Being overweight or underweight can affect ovulation.

So here’s the thing.

Most people know that the female ovaries produce estrogen, but what most people don’t know however is that our fat cells also make estrogen. To ovulate, your body needs an appropriate amount of estrogen. Too much estrogen, created by too many fat cells, can throw your hormones off and, in turn, stop ovulation from happening.

But on the other hand, being a very low body weight can also affect ovulation. Low body weight or body fat percentage can affect the ovaries and their ability to produce estrogen. This is because adequate amounts of estrogen are needed to help release the egg from the ovary.

But not only this a low body weight can stop menstruation altogether. You see menstruation and ovulation require lots of energy from the body. So, a woman that is not consuming adequate amounts of energy signals to the body that it is in a state of stress. As a result, the body shuts off all unnecessary functions like reproduction. Our body does this to conserve energy in order to keep you safe.



Stress is more than financial worries, work or school deadlines. It includes stressors like intense exercise and a lack of sleep.


The hypothalamus (a region in the brain) is in charge of the stress response but it also sends signals to the pituitary gland (another region in the brain) to produce hormones. The pituitary gland is considered the 'control centre' for reproduction and it is highly sensitive to stress. So when a woman is experiencing long term stress and cortisol (the primary stress hormone) levels are chronically elevated normal levels of reproductive hormones are suppressed resulting in no ovulation.

Causes of PCOS

As discussed women with PCOS suffer from high male hormones. But you might be wondering, well what exactly is causing the high androgens in the first place?

Well, this is where things can get a little bit complicated. There isn't one thing that is causing high androgens in every woman with PCOS. In fact, there are three potential causes: insulin resistance, high cortisol and inflammation.

Insulin Resistant PCOS

Insulin resistance is the most common root cause of PCOS, with about 70% of women suffering from this.

So our bodies main source of energy is glucose (sugar) and we get this from the food we eat. The sugar we get from food enters our bloodstream after digestion. Now insulin is a hormone created by the pancreas, that signals to our cells to take sugar out of the bloodstream and use it as fuel. But when someone is insulin resistant, the cells don't respond to the signal insulin is giving. As a result, there is a build-up of sugar in the bloodstream.

To reduce blood sugar levels the pancreas starts producing even more insulin. High levels of insulin in the body then has the unwanted side effect of telling the ovaries to produce more androgens. Which then causes the PCOS symptoms women experience.

We often think overconsumption of carbs/simple sugars, to be the only reason for too much insulin. But, lifestyle factors such as inadequate sleep and lack of exercise can also cause insulin resistance.

High Cortisol causes Adrenal PCOS

When we are stressed we go into fight or flight mode. Our body evolved to keep us safe in the wild and cannot distinguish between you needing to run away from a tiger and you feeling stressed due to a work meeting. The body responds in the same way, with the adrenals releasing cortisol into the bloodstream.

In addition to the release of cortisol, the adrenals produce androgens including DHEA, DHEA-S, and androstenedione. These male hormones try to protect the body from the damaging effects of too much cortisol. However, the longer cortisol stays high, the more androgens are released. This then causes a hormonal imbalance and the development of PCOS.

What Causes Stress

We often associate stress as running late for work or studying for an exam. But stress is more than that. Below is a list of possible stressors that you may be experiencing on a daily basis.

  • Over-Exercising and High-Intensity Exercise
  • Low-Calorie Dieting
  • Inflammation
  • Lack of Sleep
  • Over Consuming Caffeine
  • Autoimmune Disease
  • Environmental Toxins

This is the root cause of about 20-30% of women’s PCOS.

How Inflammation Causes PCOS

Inflammation is a response the immune system takes to protect us from viruses and bacteria.

Researchers have found that PCOS women suffer from chronic inflammation. This inflammation occurs when the immune system believes it is always under threat.

A study found inflammation directly stimulates the ovary to produce male hormones. And as a result PCOS symptoms.

You might be wondering.

What Causes Inflammation?

There is no clear answer to this question, inflammation can be caused for various reasons. Below are just a few of the possible causes of inflammation in women with PCOS.

  • Environmental toxins
  • Stress
  • Chronic infections
  • Over-exercising
  • Lack of nutrients including antioxidants
  • Allergies
  • Eating foods, you are intolerant to
  • Unhealthy gut

The role of Epigenetics in PCOS

Epigenetics is the study of how heritable chemical marks on our DNA can adjust the expression of our genes. In other words, epigenetics control which genes are turned on and off. But it's not just about the marks that we inherit. The science is showing, that environmental factors like diet and lifestyle can also impact our genes for better or worse.

Studies reveal epigenetic changes can occur in women who are predisposed to PCOS. Meaning the gene is turned on and the symptoms are experienced.

So do not feel helpless if you are genetically predisposed to have PCOS. You can overcome it, by making beneficial diet and lifestyle choices that can potentially 'turn off' this part of your genetics. How cool is that? The body really is an amazing thing!

To find out the root cause of your PCOS, check out my Types of PCOS: Ultimate Guide (2020).

Bottom Line

No simple or straightforward explanation exists for what causes PCO and PCOS. But research suggests PCO and PCOS occur due to hormonal imbalances.

A discussed, despite there being a genetic influence, symptoms of PCOS can be reversed. The study of epigenetics suggests we no longer have to feel like victims to our genes. We have the ability to reverse it.

So, I have covered the differences between PCO and PCOS. You might now be wondering.

How Do I Know If I Have PCO Or PCOS?

As discussed in the symptoms section, there are clear differences between PCO and PCOS so it is possible to make the distinction. But it is always best to visit your doctor to undergo the necessary tests.

What are the PCO Tests?

Doctors diagnose polycystic ovaries using an ultrasound. A transvaginal ultrasound is considered the gold standard for diagnosing PCO. But in cases where the woman is a virgin, doctors will do an abdominal ultrasound.

Doctors undertaking an ultrasound will be looking out for the features listed below.

Figure 1: PCOS, Copyright-free use, via Wikimedia Commons

Features include:

  • increased follicle number per ovary (FNPO) at least one ovary with 12 or more small ‘cysts’ (2–8 mm) is defined as polycystic.
  • individual follicles are generally similar in size and measure 2-9 mm in diameter
  • the follicles arranged on the edge of the ovary; this can give a string of pearls appearance (as seen in Figure 1)
  • an ovarian volume greater than 10 mL- As the number of eggs accumulate, the ovaries become larger. An ultrasound will assess the volume of each ovary by measuring the length, width and depth.
  • significantly greater ovarian stromal volume (the outer part of the ovary is made up of connective tissue called ‘a stroma’) and blood vessels than normal ovaries. The ultrasound detects this based on brightness and color.

The features mentioned above can be present in either one or both ovaries.

What are the PCOS Tests?

As mentioned in the 'What is PCOS?' section above, to be diagnosed with PCOS, you must meet 2 out of the 3 from the Rotterdam Criteria.

So to test you against this criteria, a doctor will carry out a blood test and ultrasound. But before this, they will run a medical history test and a physical exam.

The doctor will perform the analysis in this order.

Medical History: The doctor may ask questions about your health, menstrual cycle and family history. Finding out if you have an irregular menstrual cycle (number 2 in the Rotterdam Criteria).

Physical Exam: During a physical examination, the doctor may check your blood pressure, body weight and waist size.

Ultrasound: An ultrasound of the ovaries can identify whether there are ‘cysts’ on your ovaries (number 3 on the Rotterdam Criteria). The ultrasound will either be an abdominal or transvaginal scan.

Blood Test: An ultrasound is not enough to diagnose PCOS. This is because if doctors only looked for ≥12 follicles, based upon the definition of polycystic ovaries then experts indicate 73% of the healthy female population would have met this definition.

To know for sure if you have PCOS, you need to get a blood test. Using the blood test, your doctor can see your hormone levels and establish if you have high androgens (number 1 in the Rotterdam Criteria). Your doctor will be looking out for high male hormones like testosterone. But also further signs of hormone imbalance such as low progesterone and low SHBG levels.


In a Nutshell

An ultrasound will indicate if an ovary is polycystic, but this is not enough to diagnose PCOS. A blood test along with an ultrasound is necessary to be formally diagnosed with PCOS.

PCOS is a hormonal condition so without evidence of high male hormones, a PCOS diagnosis cannot be given. So be aware that if you only have polycystic ovaries this does not always mean you have PCOS. An ovary with multiple follicles is not considered a problem if there is no other evidence of high male hormones.

Do You Have PCO Or PCOS?

To sum up, PCOS is a complex hormonal condition in which women produce too many male hormones. While PCO is the development of multiple follicles in the ovary without any evidence of high male hormones. Both PCOS and PCO have some similar symptoms. Such as polycystic ovaries, irregular period, a lack of ovulation and infertility. The key difference, however, is that PCOS women also struggle with symptoms like, acne, facial hair and hair loss because of the high male hormones.

Do The Tests

If you are suffering from any of the PCOS symptoms discussed, it is critical that you visit your doctor immediately. Doctors use an ultrasound to view a female’s ovaries and take a blood test to check hormone levels.

PCO and PCOS symptoms can be managed when you address what is causing the hormone imbalance.


Hey there! I am Despina Pavlou, founder of PCOS Oracle, certified personal trainer and corrective exercise specialist.  I want to share with you the diet and lifestyle changes I made to naturally reverse my PCOS and achieve hormonal balance. I believe using my holistic approach you too can take back control from PCOS.

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