The true difference between PCOS, and Polycystic ovaries (PCO)

I have cysts in my ovaries, so I have PCOS” is a much heard, but incorrect, statement. It is a common misconception that all ovarian cysts are associated with polycystic ovarian syndrome (PCOS). This confusion leads to incorrect diagnosis and insufficient treatment, but also to a head full of worries.

First of all, what is an ovarian cyst?

Cysts are fluid filled sacs, which may occur either on the inside, or on the outside of the ovary, or both ovaries. Ovarian cysts are common, usually asymptomatic and an incidental finding on ultrasound. Because of this, the exact prevalence of ovarian cysts is unknown, but it has been estimated to be between 5 and 10% in women of reproductive age (1).

What is Polycystic ovarian syndrome (PCOS)?

PCOS is the most common fertility issue in women worldwide, characterized by a range of symptoms caused by metabolic and hormonal imbalance. PCOS is not just diagnosed by cysts on the ovaries, and can even be diagnosed without them. To be more specific: you get the diagnosis PCOS if you score two out of three criteria (2):

  1. A high testosterone and/or symptoms that are associated with a high testosterone, such as: acne, excessive hair growth particularly on your face, back and chest, or the opposite - excessive hair loss.

  2. A long or irregular cycle (a cycle longer than 38 days and shorter than 6 months), or just no cycle at all (no period for more than 6 months).

  3. With an ultrasound, we can detect a large number of follicles or cysts in one or both of the ovaries, which can look like a string of pearls. Having 12 or more in one of the ovaries is a symptom of PCOS.

In short: PCOS is a metabolic disorder which can disrupt many processes in the body. Despite the widespread impact of PCOS, the syndrome is best known for causing problems with ovulation. Follicles that are supposed to grow and ovulate under hormonal control each month, may fail to do so. Instead of ovulating, they can then develop into the characteristic cysts that we see on ultrasound.

If you are interested in knowing more about PCOS, read our blogs on PCOS and fertility or general health.

What are Polycystic ovaries (PCO)?

PCO and PCOS are not the same thing. PCO simply refers to the polycystic pattern seen on ultrasound (similar to PCOS), however in PCO the metabolic component is absent. Therefore other PCOS-like symptoms, or hormonal abnormalities, are absent too.

‘Polycystic ovaries’ refers to an abnormal behavioural pattern of the growing follicles. This may refer to the amount of follicles, the pattern in which they present, or their appearance. PCO is usually an incidental finding on examination and can appear normal again with a follow-up scan. In addition, polycystic ovaries are very common, not dangerous, and do not cause any symptoms (such as abdominal pain). While PCOS occurs in approximately 10% of women (3), the prevalence of PCO is about 15 to 30% (4, 5) .

Another difference between PCOS and PCO, is that PCO is not associated with ovulation problems and thus normal periods exist. PCO is also not related to long-term health, does not cause fertility issues, pregnancy complications or other hormonal imbalance. All very important differences!

Functional vs Pathological cysts: differences and similarities

Next to PCOS and PCO, other types of ovarian cysts exist. There is a distinction to be made between normal ovarian cysts (also called ‘functional’ or physiological), and pathological cysts. Pathological cysts refer to an abnormal pattern, but can either be benign or malignant.

Functional cysts

During each cycle a few follicles grow under hormonal stimulation. These are distributed normally throughout the ovaries and grow during the first two weeks of your cycle. One egg - or two eggs - ovulate, while the other follicles dissolve. Some cysts may occur during this process. These are called functional cysts, of which two main types exist:

  • A follicular cyst (when the follicle that was supposed to ovulate, fails to do so), or

  • A corpus luteum cyst (which forms in the sac that is left behind in the ovary after releasing an egg).

Both cysts generally cause little to no pain, and resolve spontaneously. On ultrasound they will appear as perfectly round fluid filled balls of different sizes. Surgical removal is only necessary with larger cysts, since these can rupture, or cause twisting of the ovary.

Pathological cysts

Abnormal cysts develop through different processes. We have listed the most common types for you:

  • Dermatomas (also ‘dermoid cysts’ or ‘teratomas’) are one of the most common types of cyst in women between 20 and 40 years old, and account for about 70% of ovarian masses (6). These cysts consist of an egg cell, but may also contain fat tissue, teeth or hair. Surgical removal is offered as treatment, since a low percentage of dermatomas can become malignant.

  • Endometriomas can occur in women with endometriosis. Another more descriptive name for this type is a ‘chocolate cysts’, referring to the old dark blood that they contain. About 17 to 44% of women with endometriosis develop these cysts, which are most commonly found on the ovaries (7).

  • Hemorrhagic cysts can develop after ovulation, when the follicles bleed and encapsulate this at the same time.

  • Cystadenomas are most common in women over 40 years old, and have a different origin. These cysts develop from the outer part of the ovary, which means that they often grow into the abdomen, attached to the ovary through a stalk.

Can ovarian cysts impact my fertility?

Yes, some types of ovarian cysts may impact your fertility, depending on the underlying cause, such as PCOS. However the good news is that most cysts do not.

In the worst case scenarios, some cysts need to be surgically removed, which may sometimes result in removal of the whole ovary. Research has shown that this does not impact fertility, and chances of conceiving are similar in women with one or two ovaries (8).

What should I look out for?

As we said, ovarian cysts often present without symptoms and are usually harmless. Still, there are some signs you can look out for:

  • Irregular menstrual cycles, and symptoms associated with a high testosterone (PCOS).

  • Extremely painful or uncomfortable, and heavy periods (endometriosis).

  • Unimaginable and sudden abdominal pain, often in combination with nausea and vomiting (rupture of a cyst of twisting of the ovary).

  • Abdominal distention, frequent urination (large cysts, or other masses).

  • Unexplained weight loss (cancerous masses)

If you are experiencing any of these symptoms, or you are worried about ovarian cysts for another reason, this should be discussed with your family doctor.

How can I know if I have ovarian cysts?

The only way to find out if you actually have an ovarian cyst/polycystic ovaries, is by having an ultrasound performed (or other imaging, such as CT/MRI). This will usually only happen on indication, which means: if you present with symptoms or your doctor has another reason for suspecting ovarian problems.

As mentioned before, most often cysts are found incidentally when performing an ultrasound for a different reason (e.g. placing of an IUD). Depending on the type of cyst, your doctor will either wait-and-see, or refer you for treatment.

Can I avoid getting ovarian cysts?

Unfortunately ovarian cysts can’t be prevented, but we can make sure to manage your symptoms as well as possible. And, as always, a healthy life-style goes a long way.

Worried you might have an ovarian cyst?

Wait no longer, and make sure to go see your doctor!


  1. Mobeen S, Apostol R. Ovarian Cyst. [Updated 2021 Jun 10]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2021 Jan-. Available from:

  2. Rotterdam ESHRE/ASRM-Sponsored PCOS Consensus Workshop Group (2004). Revised 2003 consensus on diagnostic criteria and long-term health risks related to polycystic ovary syndrome. Fertility and sterility, 81(1), 19–25.

  3. Norman, R. J., Dewailly, D., Legro, R. S., & Hickey, T. E. (2007). Polycystic ovary syndrome. Lancet (London, England), 370(9588), 685–697.

  4. Koivunen, R., Laatikainen, T., Tomás, C., Huhtaniemi, I., Tapanainen, J. and Martikainen, H. (1999), The prevalence of polycystic ovaries in healthy women. Acta Obstetricia et Gynecologica Scandinavica, 78: 137-141.

  5. Farquhar CM, Birdsdall M, Manning P, Mitchell JM.Transabdominal versus transvaginal ultrasound in the diag-nosis of polycystic ovaries of randomly selected women.Ultrasound Obstet Gynecol 1994; 4: 54–9

  6. Sinha, A., & Ewies, A. A. (2016). Ovarian Mature Cystic Teratoma: Challenges of Surgical Management. Obstetrics and gynecology international, 2016, 2390178.

  7. Hoyle AT, Puckett Y. Endometrioma. [Updated 2021 Jul 25]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2021 Jan-. Available from:

  8. Bellati, F., Ruscito, I., Gasparri, M.L. et al. Effects of unilateral ovariectomy on female fertility outcome. Arch Gynecol Obstet 290, 349–353 (2014).