Polycystic Ovary Syndrome

Polycystic ovary syndrome (PCOS) is a common endocrine disorder of reproductive-age women defined by a combination of ovulatory dysfunction, clinical or biochemical hyperandrogenism, and polycystic ovarian morphology. It is the leading cause of normogonadotropic anovulation and is associated with metabolic features such as insulin resistance.

Definition

PCOS is a heterogeneous endocrine syndrome diagnosed, under the Rotterdam criteria, when at least two of three features are present — oligo- or anovulation, clinical or biochemical hyperandrogenism, and polycystic ovarian morphology — after exclusion of conditions that mimic it.

Scope

This topic covers the definition and diagnostic criteria of PCOS, its core endocrine and metabolic features, and its place as the commonest cause of anovulatory infertility. It is a reference overview of the condition and its concepts; it does not provide diagnostic or treatment instructions for individuals.

Core questions

• How do the Rotterdam, NIH, and Androgen Excess Society definitions of PCOS differ?
• What is the role of hyperandrogenism and insulin resistance in the syndrome's pathophysiology?
• Why must other causes of hyperandrogenism and anovulation be excluded before diagnosing PCOS?

Key concepts

• Rotterdam diagnostic criteria
• Hyperandrogenism (clinical and biochemical)
• Oligo-ovulation and anovulation
• Polycystic ovarian morphology on ultrasound
• Insulin resistance and compensatory hyperinsulinemia
• Diagnosis of exclusion
• Metabolic and cardiovascular risk associations

Mechanisms

PCOS reflects interacting endocrine and metabolic disturbances. Increased ovarian androgen production, often amplified by hyperinsulinemia arising from insulin resistance, disrupts normal follicular development so that follicles arrest and ovulation becomes infrequent or absent. Altered gonadotropin secretion, with a relatively elevated LH-to-FSH drive, further contributes to anovulation and to the accumulation of small antral follicles seen as polycystic morphology. The condition is heterogeneous, and no single mechanism explains all phenotypes, which is why it is defined by a constellation of features rather than one marker.

Clinical relevance

Because PCOS is the most frequent cause of anovulatory infertility and carries metabolic associations, understanding its criteria is central to reproductive endocrinology. This entry describes the syndrome for educational orientation; lifestyle, pharmacologic, and fertility management decisions belong to individualized clinical care and are not addressed here as recommendations.

Epidemiology

PCOS is among the most common endocrine disorders in reproductive-age women, with prevalence estimates varying by the diagnostic criteria applied; the broader Rotterdam criteria yield higher estimates than the older NIH definition. Affected women show, on average, differences in dietary and physical-activity patterns and a higher burden of insulin resistance.

History

The syndrome was first described by Stein and Leventhal in 1935 as the association of amenorrhea with enlarged polycystic ovaries. Diagnostic criteria evolved through the 1990 NIH conference, the 2003 Rotterdam consensus that broadened the definition to require two of three features, and later evidence-based international guidelines that standardized assessment.

Debates

Which diagnostic criteria should define PCOS?

The NIH, Rotterdam, and Androgen Excess and PCOS Society definitions differ in whether polycystic morphology alone, without hyperandrogenism, can support the diagnosis, producing different prevalence estimates and phenotype groupings.

Key figures

• Irving Stein
• Michael Leventhal
• Helena Teede
• Richard Legro

Seminal works

• rotterdam-2004
• legro-2013
• teede-2018

Frequently asked questions

What are the Rotterdam criteria for PCOS?

The Rotterdam criteria diagnose PCOS when at least two of three features are present — oligo- or anovulation, clinical or biochemical hyperandrogenism, and polycystic ovarian morphology on ultrasound — once other causes have been excluded.

Why is PCOS called a diagnosis of exclusion?

Several conditions, such as thyroid disease, hyperprolactinemia, and non-classic congenital adrenal hyperplasia, can mimic its features, so they must be ruled out before the diagnosis is made.