What is Polycystic Ovary Syndrome (PCOS)?

Introduction

Polycystic Ovary Syndrome (PCOS) is the most common hormonal disorder affecting women of reproductive age, with a prevalence of approximately 4–21% depending on the diagnostic criteria used and the population studied. It is one of the leading causes of female infertility, a significant driver of metabolic disease risk, and a major contributor to psychological distress in millions of women worldwide.

Despite its prevalence, PCOS is frequently misunderstood — both by patients and healthcare providers. It is often reduced to "having cysts on your ovaries" (a misleading simplification) or dismissed as a cosmetic or fertility issue, when in fact it is a complex, multisystem endocrine-metabolic syndrome with lifelong health implications.

Defining PCOS

PCOS is named for the polycystic appearance of the ovaries on ultrasound — dozens of small, immature follicles arrested at an early stage of development. But "polycystic ovaries" alone do not make a diagnosis of PCOS. Up to 20–30% of healthy women with no symptoms can have polycystic-appearing ovaries on ultrasound.

A diagnosis of PCOS requires the presence of two out of three Rotterdam criteria (established in 2003 and still the most widely used today):

• Hyperandrogenism: Clinical (hirsutism
• acne
• androgenic alopecia) or biochemical (elevated serum testosterone or other androgens)
• Ovulatory dysfunction: Oligo-ovulation or anovulation
• manifesting as irregular or absent menstrual periods
• Polycystic ovarian morphology: ≥12 small follicles per ovary on transvaginal ultrasound
• or elevated AMH (anti-Müllerian hormone)

Crucially, two criteria (any combination) are sufficient — a woman can have PCOS without visible polycystic ovaries on ultrasound, if she has hyperandrogenism and irregular cycles.

The Core Features

Hyperandrogenism

Excess androgens (testosterone, androstenedione, DHEA-S, and recently characterised 11-oxygenated androgens) produce clinical signs: hirsutism (excess coarse hair in androgen-sensitive areas: upper lip, chin, chest, abdomen, inner thighs

Ovulatory Dysfunction

Most women with PCOS have oligomenorrhoea (cycles >38 days, fewer than 9 periods/year) or amenorrhoea (absent periods). This results from chronic anovulation — the HPO axis fails to produce the appropriate FSH and LH signals for sequential follicle development and ovulation. Instead, multiple follicles are stimulated but none matures fully or ovulates. The result is irregular bleeding patterns and difficulty conceiving.

Polycystic Ovarian Morphology

The characteristic ultrasound appearance — 12 or more small follicles (each 2–9 mm in diameter) arranged peripherally in the ovary — resembles a "string of pearls." Ovarian volume is typically enlarged (>10 mL). The 2023 International PCOS Guideline recognises that AMH (anti-Müllerian hormone

Associated Features

Beyond the three diagnostic criteria, PCOS is associated with a cluster of metabolic and psychological features:

• Insulin resistance: Present in 50–80% of women with PCOS
• regardless of BMI. Hyperinsulinaemia amplifies ovarian androgen production and reduces SHBG.
• Obesity: 40–60% of women with PCOS are overweight or obese; however
• a significant minority are lean or "normal weight" PCOS.
• Metabolic syndrome: Elevated fasting glucose
• dyslipidaemia
• hypertension
• and central adiposity — present in up to 40% of PCOS patients.
• Type 2 diabetes: Up to 40% of PCOS women develop type 2 diabetes by their 40s.
• Sleep apnoea: Highly prevalent
• especially in obese women with PCOS — up to 50%.
• Mental health: Anxiety and depression rates 2–3 times higher than in the general population.
• Infertility: PCOS is the leading cause of anovulatory infertility.

Who Gets PCOS?

PCOS affects women across all ethnicities, though prevalence and phenotype vary. South Asian women tend to have more severe insulin resistance relative to their BMI. Women of Middle Eastern descent have higher clinical hyperandrogenism rates. The syndrome appears in puberty (or earlier, with maternal and in utero influences) and persists throughout the reproductive years, often evolving post-menopause into metabolic risk without the hormonal features.

Is There a Cure?

There is currently no cure for PCOS. However, it is highly manageable. Treatment is tailored to the woman\'s primary concerns (irregular periods, acne/hirsutism, fertility, metabolic risk) and always begins with lifestyle modification — which, even modestly, can restore ovulation and improve most features of the syndrome.

References: Rotterdam Consensus Criteria 2003; 2023 International PCOS Guideline; Bozdag G et al., Hum Reprod 2016 (prevalence); Teede H et al., Nat Rev Endocrinol 2023.