Polycystic Ovary Syndrome

Polycystic ovary syndrome (PCOS) is a common endocrine disorder of reproductive-age women defined by some combination of hyperandrogenism, ovulatory dysfunction, and polycystic ovarian morphology. From the metabolic standpoint it is closely tied to insulin resistance and obesity, which both contribute to and worsen its hormonal and reproductive features, placing it at the crossroads of reproductive and metabolic endocrinology.

Definition

Polycystic ovary syndrome is a heterogeneous endocrine disorder, typically diagnosed when at least two of the following are present after excluding other causes: clinical or biochemical hyperandrogenism, oligo- or anovulation, and polycystic ovarian morphology on ultrasound; it is frequently accompanied by insulin resistance and metabolic disturbance.

Scope

The topic covers the diagnostic concept of PCOS, its hormonal and metabolic features, the central role of insulin resistance, and its long-term cardiometabolic associations. It is framed here as a metabolic-endocrine disorder; a companion node under ovulatory dysfunction addresses its reproductive dimension. The entry is a reference overview and not a basis for individual diagnosis or treatment.

Core questions

• What features define PCOS, and why do diagnostic criteria vary?
• How does insulin resistance link the reproductive and metabolic features of PCOS?
• What long-term metabolic risks are associated with the syndrome?

Key concepts

• Hyperandrogenism
• Ovulatory dysfunction (oligo- or anovulation)
• Polycystic ovarian morphology
• Insulin resistance and compensatory hyperinsulinaemia
• Diagnosis of exclusion and heterogeneous phenotypes
• Cardiometabolic risk association

Mechanisms

Insulin resistance with compensatory hyperinsulinaemia is a central feature in many women with PCOS. Elevated insulin acts on the ovary to augment androgen production and lowers hepatic sex-hormone-binding globulin, raising free androgen levels; the resulting hyperandrogenism disrupts follicular development and contributes to anovulation. Excess adiposity amplifies insulin resistance, creating a self-reinforcing loop between metabolic and reproductive disturbance. These mechanisms underlie the syndrome's frequent association with impaired glucose tolerance, dyslipidaemia, and increased cardiometabolic risk.

Clinical relevance

PCOS is one of the most common endocrine disorders in reproductive-age women and a frequent context for insulin resistance and metabolic risk, making it important across reproductive and metabolic medicine. This entry summarises its definition, mechanisms, and associations for educational reference and does not provide individualised diagnostic criteria, drug choices, or dosing.

Epidemiology

PCOS is among the most prevalent endocrine disorders in women of reproductive age, with reported prevalence varying substantially by the diagnostic criteria applied. It is strongly associated with overweight and obesity and with an elevated risk of impaired glucose tolerance and type 2 diabetes.

Evidence & guidelines

Major society and international evidence-based guidelines define the diagnostic approach and frame management of PCOS, and authoritative reviews synthesise its pathophysiology. This entry references those guidelines and reviews to describe the syndrome but does not reproduce their clinical recommendations for individual application.

History

The syndrome was described by Stein and Leventhal in 1935 as an association of amenorrhoea with enlarged polycystic ovaries. Over subsequent decades its definition broadened from the ovarian morphology to a hormonal and metabolic syndrome, with successive consensus criteria (including the recognition of hyperandrogenism and ovulatory dysfunction) and growing emphasis on insulin resistance and cardiometabolic risk.

Debates

Which diagnostic criteria best define PCOS?

Different consensus criteria yield different phenotypes and prevalence estimates, and debate continues over how to define the syndrome consistently while capturing its heterogeneity.

Key figures

• Richard Legro
• Helena Teede
• Hector Escobar-Morreale

Seminal works

• legro-2013
• teede-2018
• escobar-morreale-2018

Frequently asked questions

Why is PCOS discussed under energy metabolism and obesity?

Because insulin resistance and obesity are central to its pathophysiology, linking its reproductive features to metabolic disturbances such as impaired glucose tolerance and increased cardiometabolic risk.

How is PCOS defined?

It is commonly diagnosed when at least two of hyperandrogenism, ovulatory dysfunction, and polycystic ovarian morphology are present after excluding other causes, which is why prevalence estimates vary with the criteria used.