Polycystic ovary syndrome, or PCOS, is a hormonal disorder that affects an estimated 10 to 13% of women of reproductive age worldwide. In medical terms, it is classified as an endocrine and metabolic condition defined by a combination of excess androgen hormones, irregular ovulation, and characteristic changes to the ovaries visible on ultrasound. Up to 70% of women with PCOS remain undiagnosed, partly because the condition looks different from person to person.
The Rotterdam Diagnostic Criteria
The standard medical framework for diagnosing PCOS is known as the Rotterdam criteria, established by an international consensus panel and still used today. Under these criteria, a diagnosis requires the presence of at least two of three clinical findings: hyperandrogenism, ovulatory dysfunction, and polycystic ovarian morphology. Because only two of the three are needed, a woman can have PCOS without actually having visible cysts on her ovaries, which is one of the most commonly misunderstood aspects of the condition.
This two-out-of-three approach also means PCOS presents in several distinct subtypes. One person may have excess androgens and irregular periods but normal-looking ovaries. Another may have polycystic ovaries and high androgen levels but still ovulate regularly. Each combination is considered a valid diagnosis, though the metabolic risks can vary between subtypes.
What “Hyperandrogenism” Actually Means
Hyperandrogenism refers to higher-than-normal levels of androgens, a group of hormones that includes testosterone. In clinical practice, it can be identified in two ways: through blood tests showing elevated androgen levels (biochemical hyperandrogenism) or through visible physical signs (clinical hyperandrogenism). The most common physical sign is hirsutism, which is excess hair growth in areas where women typically have minimal hair, such as the face, chest, and back.
Doctors assess hirsutism using the modified Ferriman-Gallwey scoring system, which grades hair growth across nine body areas on a scale. A score of 4 to 6 or above is generally used to flag hirsutism in a clinical setting, though the threshold can vary by ethnicity. Evidence of PCOS, such as elevated androgen levels or irregular cycles, appears in about 50% of women who score between 3 and 5 on this scale, and in 70 to 90% of those who score above 5. Other clinical signs of hyperandrogenism include persistent acne and thinning hair on the scalp.
Ovulatory Dysfunction
Ovulatory dysfunction is the medical term for irregular or absent ovulation. In practical terms, this shows up as unpredictable menstrual cycles, cycles that are consistently longer than 35 days, or periods that stop entirely for months at a time. Some women with PCOS do ovulate, but infrequently or inconsistently, which is why the condition is one of the leading causes of difficulty conceiving.
The hormonal mechanism behind this involves an imbalance between two key signaling hormones from the pituitary gland. In many women with PCOS, the ratio of luteinizing hormone (LH) to follicle-stimulating hormone (FSH) is elevated to 1:1 or higher, when it would normally be lower. This imbalance disrupts the normal process by which a single egg matures and is released each month. Instead, multiple small follicles begin developing but none reaches full maturity, which is what creates the characteristic appearance on ultrasound.
What “Polycystic Ovaries” Looks Like on Imaging
The term “polycystic” is somewhat misleading. The small round structures visible on ultrasound are not true cysts but immature follicles, each measuring 2 to 9 millimeters. Under the most current 2023 international guidelines, polycystic ovarian morphology (PCOM) is defined as 20 or more of these follicles in at least one ovary when using modern transvaginal ultrasound technology.
When image quality is limited or the scan is performed through the abdomen rather than transvaginally, the threshold drops to either an ovarian volume of 10 milliliters or more, or 10 or more follicles visible per cross-section of the ovary. These updated numbers reflect improvements in ultrasound resolution. Older machines detected fewer follicles, so earlier thresholds were set lower and would now produce too many false positives with current equipment.
It is worth noting that polycystic-appearing ovaries on ultrasound are common in young women who do not have PCOS. This is why the finding alone is never sufficient for a diagnosis, and why the Rotterdam criteria require at least one additional feature.
Metabolic and Cardiovascular Risks
PCOS is not purely a reproductive condition. It carries significant metabolic consequences that can affect long-term health. Insulin resistance is present in a majority of women with the syndrome, regardless of body weight. The body produces extra insulin to compensate, and this excess insulin further stimulates the ovaries to produce more androgens, creating a self-reinforcing cycle.
The downstream effects are measurable. Women with PCOS have significantly higher rates of type 2 diabetes, prediabetes, and metabolic syndrome compared to women without the condition. A large prospective study published in the European Journal of Endocrinology found that by their mid-40s, women with PCOS had elevated blood pressure and were using blood pressure medication at roughly double the rate of women without the diagnosis, with about 23 to 31% on antihypertensive medication compared to around 15% in the general population. These cardiovascular risks persist regardless of which specific diagnostic criteria were used to identify the PCOS.
How PCOS Is Medically Classified
In formal medical coding, PCOS falls under the International Classification of Diseases as code E28.2, referring to polycystic ovarian syndrome. It sits within the broader category of ovarian dysfunction under endocrine, nutritional, and metabolic diseases. This classification reflects the modern understanding that PCOS is a systemic metabolic disorder with reproductive consequences, not simply an ovarian problem.
Clinically, PCOS is sometimes divided into phenotypes based on which combination of the Rotterdam criteria are present. Phenotype A (all three features) and Phenotype B (hyperandrogenism plus ovulatory dysfunction) tend to carry the highest metabolic risk. Phenotype C (hyperandrogenism plus polycystic ovaries, with regular cycles) and Phenotype D (ovulatory dysfunction plus polycystic ovaries, without excess androgens) are generally considered milder metabolic profiles, though all phenotypes benefit from long-term monitoring.
What Gets Ruled Out First
Because the symptoms of PCOS overlap with several other conditions, diagnosis is partly a process of elimination. Before confirming PCOS, clinicians test for thyroid disorders, elevated prolactin levels, and a condition called non-classic congenital adrenal hyperplasia, all of which can mimic PCOS symptoms. Cushing’s syndrome and androgen-secreting tumors are rarer but also considered when androgen levels are extremely high. Once these are excluded and at least two Rotterdam criteria are confirmed, the diagnosis stands.