What Is PCOS? An Evidence-Based Guide to Symptoms, Diagnosis, and Testing

📷 [String of Pearls sign on ultrasound. Source: ResearchHub.]

What Is PCOS? An Evidence-Based Explanation

Irregular periods, high androgen symptoms, and insulin resistance are often mentioned together, but what does PCOS actually mean?

Polycystic Ovary Syndrome, or PCOS, is one of the most common endocrine disorders in reproductive-age women. Reported prevalence varies depending on which diagnostic criteria are used, but large reviews estimate it at about 6% under NIH criteria and around 10% under Rotterdam criteria. [1]

Despite its name, PCOS is not simply a condition of “cysts on the ovaries.” It is a heterogeneous syndrome defined by combinations of ovulatory dysfunction, hyperandrogenism, and polycystic ovarian morphology, also called PCOM. Ovarian appearance alone does not define PCOS. [2][3]

In PCOS, follicle development and ovulation can be disrupted, and multiple small follicles may be seen on ultrasound. Some people describe this appearance as a “string of pearls,” but that ultrasound pattern is only one possible feature of PCOS, not a requirement for diagnosis. [2][3]

The Three Core Features of PCOS

1. Ovulatory Dysfunction

This usually appears as irregular or infrequent menstrual cycles, such as cycles longer than 35 days, fewer than eight periods per year, or absent periods.

However, ovulatory dysfunction can still occur even when cycles seem regular. If needed, ovulation can be assessed with serum progesterone. [3]

2. Hyperandrogenism

Hyperandrogenism means excess androgen activity. It may appear clinically as hirsutism, acne, or female pattern hair loss, or biochemically on blood testing.

Current guidelines recommend total testosterone and free testosterone as first-line tests for biochemical hyperandrogenism. Free testosterone is often estimated using the free androgen index, or FAI. If those results are not clearly elevated but suspicion remains, androstenedione or DHEAS may sometimes be considered, although they are less specific. [3]

3. Polycystic Ovarian Morphology (PCOM)

PCOM is an ultrasound-defined feature. In adults, follicle number per ovary is now considered the most effective ultrasound marker. The current threshold is FNPO greater than or equal to 20 in at least one ovary when high-quality ultrasound is available.

If older technology is used or image quality is limited, ovarian volume greater than or equal to 10 mL or follicle number per section greater than or equal to 10 can be used instead. [3]

When ultrasound is indicated, the transvaginal approach is the most accurate for evaluating PCOM in adults. But if irregular cycles and hyperandrogenism are already present, ultrasound is not required for diagnosis. [3]

How PCOS Is Diagnosed

Current diagnosis is based on the Rotterdam framework, refined by the 2018 and 2023 International Evidence-Based PCOS Guideline.

In adults, PCOS is diagnosed when two of the following are present, after excluding other causes:

ovulatory dysfunction

clinical or biochemical hyperandrogenism

polycystic ovarian morphology, or elevated AMH used appropriately in adults [2][3]

Other conditions that can mimic PCOS should be excluded, including thyroid disease, hyperprolactinemia, and non-classic congenital adrenal hyperplasia. [3]

This means you can have PCOS without polycystic ovaries on ultrasound. It also means you can still have PCOS even if your cycles appear regular, if ovulatory dysfunction is confirmed in other ways. [2][3]

The Four Rotterdam Phenotypes

Because PCOS diagnosis is based on combinations of three core features, it can present in four phenotype patterns:

Phenotype A: hyperandrogenism + ovulatory dysfunction + PCOM

Phenotype B: hyperandrogenism + ovulatory dysfunction

Phenotype C: hyperandrogenism + PCOM

Phenotype D: ovulatory dysfunction + PCOM

Phenotypes A and B are often described as the more classic hyperandrogenic presentations. Some studies suggest they may show a greater metabolic burden on average, but phenotype alone does not fully predict metabolic risk. Body weight and adiposity remain major determinants of metabolic complications. [4][5]

PCOS Is More Than a Reproductive Condition

PCOS is often associated with insulin resistance, adverse lipid patterns, increased risk of impaired glucose metabolism, and important psychological symptoms such as anxiety and depression.

However, these are not themselves part of the formal diagnostic criteria. They belong to the broader clinical assessment and long-term management of PCOS. [3]

Tests Used in PCOS Evaluation

It helps to separate testing into three categories.

A. Tests that map directly to the diagnostic criteria

Ovulatory dysfunction: menstrual history, and if needed, serum progesterone

Biochemical hyperandrogenism: total testosterone, free testosterone or FAI, and sometimes androstenedione or DHEAS

PCOM: transvaginal ultrasound when indicated, or AMH in adults used appropriately [3]

B. Tests used to exclude other conditions

TSH to exclude thyroid dysfunction

Prolactin to exclude hyperprolactinemia

17-hydroxyprogesterone to help exclude non-classic congenital adrenal hyperplasia [3]

C. Tests used for metabolic assessment

fasting glucose, HbA1c, or oral glucose tolerance testing

fasting insulin

lipid profile

blood pressure and other cardiometabolic risk markers [3]

These metabolic tests are important, but they do not establish the diagnosis of PCOS on their own. [3]

What About AMH?

Anti-Müllerian hormone, or AMH, is now recognized as a possible alternative to ultrasound for defining PCOM in adults.

However, it should not be used as a single stand-alone test to diagnose PCOS. It is also not recommended for diagnosis in adolescents. In addition, AMH levels can be influenced by factors such as age and current or recent hormonal contraceptive use, so results must be interpreted carefully. [3]

Can You Get Pregnant With PCOS?

Yes. PCOS is more accurately linked to subfertility than absolute infertility.

Many people with PCOS conceive naturally, while others may need ovulation induction or other fertility treatment depending on their ovulatory pattern and overall health profile. [3]

Final Takeaway

PCOS is not just “cysts on the ovaries.” It is a syndrome defined by ovulatory dysfunction, hyperandrogenism, and sometimes polycystic ovarian morphology.

Diagnosis requires a structured evaluation, exclusion of similar conditions, and attention not only to reproductive symptoms but also to metabolic and psychological health. [2][3]