POLYCYSTIC OVARY SYNDROME

✓ Medically ReviewedDISEASEID: MDBT0285🚨 TRIAGE: URGENTICD-10: E28.2

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Definition

CLINICAL DEFINITION

Polycystic ovary syndrome (PCOS) is a heterogeneous endocrine and metabolic disorder characterised by the presence of at least two of three Rotterdam criteria: oligo-ovulation or anovulation, clinical and/or biochemical hyperandrogenism, and polycystic ovarian morphology (PCOM), after exclusion of other causes of androgen excess or ovulatory dysfunction. The 2023 International Evidence-based Guideline retained the Rotterdam diagnostic framework while updating the ultrasound threshold for PCOM to ≥20 antral follicles per ovary (2–9 mm) and endorsing serum anti-Müllerian hormone (AMH) as an alternative to ultrasound in adults. PCOS is not a single disease but a syndrome with reproductive, metabolic, and psychological dimensions.

IN PLAIN ENGLISH

Polycystic ovary syndrome (PCOS) is a common hormonal condition in women of reproductive age. It affects how the ovaries work, leading to irregular periods, extra male-type hormones, and sometimes many small follicles on the ovaries. PCOS also affects metabolism and can increase the long-term risk of diabetes and heart-related problems.

COMMON MISCONCEPTION / WHAT IT DOES NOT MEAN

PCOS is NOT simply the presence of 'cysts' on an ultrasound. Polycystic ovarian morphology (PCOM) is a common finding in healthy women and is only one of three possible criteria; it does not diagnose the syndrome on its own. PCOS is also NOT a single disease with a single cause, and it should not be diagnosed until other causes of hyperandrogenism or ovulatory dysfunction, such as thyroid disease, hyperprolactinaemia, non-classic congenital adrenal hyperplasia, or androgen-secreting tumours, have been excluded.

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Word Breakdown

poly-

=many, excessive (from Greek polys)

cyst-

=sac, bladder (from Greek kystis)

-ic

=pertaining to (from Greek -ikos via Latin -icus)

Literal Meaning: A syndrome of the ovary characterised by many sac-like structures

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Abbreviations

PCOS=Polycystic Ovary Syndrome — the canonical acronym used in clinical practice and literature

PCOM=Polycystic Ovarian Morphology — the ultrasound finding alone, which is not diagnostic of the syndrome

HA=Hyperandrogenism — the clinical and/or biochemical androgen excess that is a cardinal diagnostic feature

OA=Oligo-anovulation — infrequent or absent ovulation, a key diagnostic criterion

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Synonyms & Variants

Stein-Leventhal Syndrome›Polyendocrine Metabolic Ovarian Syndrome›

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Category-Specific Context

PCOS is classified as a Disease because it is a defined syndrome with accepted diagnostic criteria and multisystem implications. It sits at the intersection of reproductive endocrinology and metabolic medicine. The 2023 guideline recognises distinct phenotypes based on which Rotterdam criteria are present, and these phenotypes carry different metabolic risk profiles. PCOS is also the subject of a 2026 international consensus to rename it polyendocrine metabolic ovarian syndrome (PMOS), reflecting its endocrine-metabolic nature, although the ICD-10 code E28.2 remains unchanged.

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Clinical Context & Usage

CLINICAL SETTINGS

Gynaecology Outpatient DepartmentEndocrinology ClinicReproductive Medicine ClinicGeneral PracticeDermatology ClinicGeneral Medicine Ward

USAGE & DOCUMENTATION NOTES

In clinical documentation, PCOS is typically written as 'PCOS' after first definition. Notes commonly record the specific Rotterdam criteria met (e.g., 'oligo-ovulation + clinical hyperandrogenism'), the exclusion of other diagnoses, and the phenotype. Referral letters often mention the presence or absence of metabolic risk factors (BMI, glucose tolerance, lipid profile) alongside reproductive concerns. The 2023 guideline encourages documenting cardiometabolic screening and psychological wellbeing as part of the assessment, not only the gynaecological features.

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Primary Causes & Pathophysiology

PATHOPHYSIOLOGY

PCOS arises from a self-reinforcing cycle of insulin resistance and hyperandrogenism, modulated by genetic and developmental factors. Systemic insulin resistance leads to compensatory hyperinsulinaemia, which stimulates ovarian theca cells to produce excess androgens and suppresses hepatic sex hormone-binding globulin (SHBG) synthesis, raising free androgen levels. Intra-ovarian androgen excess impairs follicle maturation, producing the characteristic arrest of antral follicles and oligo-anovulation. Elevated luteinising hormone (LH) pulsatility further drives ovarian androgen production, while anti-Müllerian hormone (AMH), produced by the excessive follicle pool, contributes to follicular arrest. Adipose tissue dysfunction amplifies insulin resistance and inflammation, creating a bidirectional metabolic-reproductive cycle. The heterogeneity of PCOS reflects the variable contribution of genetic predisposition, prenatal androgen exposure, and environmental factors such as obesity.

PRIMARY CAUSES

Polygenic genetic predisposition

Familial aggregation and genome-wide association studies implicate variants affecting insulin signalling, androgen biosynthesis, and gonadotropin regulation, producing a heritable susceptibility to the insulin-hyperandrogenism cycle.

Prenatal androgen or metabolic programming

Exposure to excess androgens or endocrine-disrupting chemicals in utero may reprogram the hypothalamic-pituitary-ovarian axis and adipose tissue, predisposing to PCOS phenotype in later life.

Obesity and adipose tissue dysfunction

Excess adipose tissue amplifies insulin resistance and inflammation, exacerbating hyperinsulinaemia and free androgen excess; however, PCOS also occurs in lean individuals, indicating that obesity is an amplifier rather than a sole cause.

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Epidemiology

Prevalence:Global prevalence estimates vary by diagnostic criteria and population, with a 2024 systematic review and meta-analysis reporting a pooled prevalence of approximately 9.2% (95% CI 6.8%–12.5%) using Rotterdam criteria. The WHO estimates PCOS affects approximately 8%–13% of women of reproductive age, with up to 70% of cases remaining undiagnosed. Prevalence is higher in some ethnic groups, notably South Asian immigrants in the UK, in whom community studies have reported polycystic ovarian morphology in up to 52%.

Age Group:Primarily women of reproductive age, with onset typically manifesting in adolescence or early adulthood. Diagnosis in adolescence requires caution because anovulatory cycles and acne are common physiological features; the 2023 guideline recommends avoiding ultrasound-based diagnosis of PCOM within 8 years of menarche. PCOS persists beyond the reproductive years and is associated with ongoing metabolic risk in peri- and postmenopausal women.

Sex Predilection:Female

Geographic Distribution:PCOS is diagnosed worldwide, but reported prevalence and phenotypic expression vary with ethnicity and geographic region. South Asian and Middle Eastern populations often show higher prevalence and more severe metabolic features, including insulin resistance and hirsutism, compared with White European populations. These differences reflect genetic, environmental, and sociocultural factors, as well as variation in diagnostic access and criteria applied.

Red Flags & Triage ★

TRIAGE LEVEL

🚨 URGENT

DO NOT MISS — LIFE-THREATENING PRESENTATIONS

Rapidly progressive virilisation (clitoromegaly, voice deepening, temporal hair loss) — raises concern for an androgen-secreting tumour and requires urgent endocrine evaluation; do not attribute to PCOS without biochemical and imaging assessment.
Acute severe pelvic pain in a woman with PCOS — ovarian torsion should be considered even in the absence of an adnexal mass, because enlarged polycystic ovaries may be at risk; urgent surgical assessment is required.
Abnormal uterine bleeding in a woman with chronic anovulation — endometrial hyperplasia or carcinoma must be excluded, particularly with prolonged amenorrhoea or obesity; endometrial sampling is indicated when clinically suspected.

URGENT EVALUATION TRIGGERS

Sudden severe pelvic pain with nausea or vomiting — evaluate for ovarian torsion
Rapid virilisation or signs of androgen-secreting tumour
Heavy or prolonged uterine bleeding with hemodynamic compromise
Severe metabolic decompensation (e.g., hyperglycaemic symptoms with vomiting) in a patient with known PCOS

Contraindications & Precautions

SPECIAL PRECAUTIONS

Do not diagnose PCOS on ultrasound findings alone; PCOM is common in unaffected women and must be interpreted with ovulatory and androgen status.
Exclude pregnancy
thyroid dysfunction
hyperprolactinaemia
and non-classic congenital adrenal hyperplasia before confirming PCOS.
In adolescents
avoid overdiagnosis: anovulatory cycles and acne are common physiological findings
and pelvic ultrasound should not be used for PCOM within 8 years of menarche.
Screen for cardiometabolic risk factors (BMI
blood pressure
glucose tolerance
lipids) and psychological comorbidity at diagnosis and periodically thereafter.

Complications

DOWNSTREAM CLINICAL COMPLICATIONS

Type 2 diabetes mellitus — insulin resistance drives a 5- to 10-fold increased risk compared with women without PCOS; screening with oral glucose tolerance testing is recommended.
Endometrial cancer — chronic anovulation with unopposed oestrogen exposure is associated with an approximately 2.7- to 3-fold increased risk; risk is higher in the presence of obesity and prolonged amenorrhoea.
Cardiometabolic risk cluster — hypertension
dyslipidaemia
and obstructive sleep apnoea are more prevalent; the independent contribution of PCOS to cardiovascular events remains incompletely established
but risk-factor screening is recommended.
Psychological morbidity — depression and anxiety are more common in women with PCOS and should be screened for as part of comprehensive care.
Infertility — oligo-anovulation is a leading cause of anovulatory subfertility; ovulation induction is often required.

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Confused With (LASA & DDx) ★

LEXICAL (LASA) — SIMILAR NAMES

PCOD (Polycystic Ovarian Disease)

Often used interchangeably with PCOS in lay and some clinical contexts, but PCOD is an older, non-specific term; PCOM (polycystic ovarian morphology) describes only the ultrasound appearance and is not a diagnosis. Confusing the morphological finding with the syndrome can lead to overdiagnosis.

PMOS (Polyendocrine Metabolic Ovarian Syndrome)

The 2026 international consensus name proposed to replace PCOS. The terms refer to the same condition, but PMOS is not yet universally adopted in coding or clinical documentation; ICD-10 E28.2 remains assigned to PCOS.

CLINICAL DIFFERENTIAL DIAGNOSES (DDx)

Non-classic congenital adrenal hyperplasia (NCAH)

Key Distinguishing Feature: Basal or ACTH-stimulated 17-hydroxyprogesterone is elevated; hirsutism and oligo-ovulation can mimic PCOS, but NCAH has a distinct biochemical signature.

Hyperprolactinaemia

Key Distinguishing Feature: Serum prolactin is elevated; may cause amenorrhoea and hirsutism, but galactorrhoea and the absence of PCOM help distinguish it. Prolactin measurement is part of the exclusion work-up.

Thyroid dysfunction

Key Distinguishing Feature: Thyroid-stimulating hormone (TSH) is abnormal; hypothyroidism can cause irregular cycles, weight gain, and secondary hyperprolactinaemia, mimicking PCOS features.

Androgen-secreting ovarian or adrenal tumour

Key Distinguishing Feature: Rapid onset and progressive virilisation (clitoromegaly, voice deepening, temporal balding), markedly elevated testosterone or DHEAS, and imaging evidence of a mass; requires urgent endocrine evaluation.

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Clinical Pearls

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PCOS is a diagnosis of exclusion as well as inclusion: the Rotterdam criteria require both the presence of two features and the exclusion of mimics such as thyroid disease, hyperprolactinaemia, and NCAH. A positive ultrasound alone is insufficient.

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The 2023 guideline lowered the diagnostic weight of ultrasound by raising the follicle-count threshold to ≥20 per ovary and allowing AMH as an alternative in adults; this reduces overdiagnosis in women with incidental PCOM but requires assay-specific, age-adjusted interpretation.

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Insulin resistance is present in many women with PCOS independent of BMI, and post-load glucose testing may reveal impaired glucose tolerance when fasting glucose is normal. Cardiometabolic screening should not be deferred in lean patients.

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Endometrial protection is a core consideration in women with chronic anovulation who are not seeking pregnancy; cyclical progestogen or combined hormonal contraception should be discussed to reduce the risk of endometrial hyperplasia.

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The 2026 consensus to rename PCOS as polyendocrine metabolic ovarian syndrome (PMOS) reflects the condition's systemic nature, but the diagnostic criteria and ICD-10 code E28.2 are unchanged; clinical documentation should remain aligned with local coding and guideline terminology.

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Example Usage & SOAP

CLINICAL SENTENCE

""24-year-old woman with a 3-year history of oligomenorrhoea (cycles every 45–60 days), clinical hirsutism (modified Ferriman-Gallwey score 12), and pelvic ultrasound showing ≥20 antral follicles per ovary; TSH, prolactin, and 17-hydroxyprogesterone are normal, consistent with PCOS.""

IN A SOAP NOTE

S: 24-year-old woman reports infrequent periods every 2–3 months for 3 years, unwanted facial hair, and difficulty losing weight. O: BMI 28 kg/m²; modified Ferriman-Gallwey score 12; blood pressure 118/76 mmHg; pelvic ultrasound: ≥20 antral follicles per ovary (2–9 mm), ovarian volume 11 mL; total testosterone 2.8 nmol/L (upper limit of reference), SHBG low; TSH 2.1 mIU/L; prolactin 320 mIU/L; 17-OHP 3.1 nmol/L; fasting glucose 5.4 mmol/L; 2-hour OGTT glucose 7.6 mmol/L (impaired glucose tolerance). A: PCOS (Rotterdam criteria: oligo-ovulation + clinical hyperandrogenism + PCOM), with impaired glucose tolerance. P: Lifestyle intervention with diet and exercise; combined oral contraceptive initiated for cycle regulation and endometrial protection; repeat OGTT in 12 months; consider metformin if metabolic risk persists; screening for anxiety and depression.

DIFFERENTIAL DIAGNOSIS CONTEXT

Differential for a woman presenting with oligomenorrhoea and hirsutism: (1) PCOS — confirm two Rotterdam criteria and exclude mimics; (2) non-classic congenital adrenal hyperplasia — check 17-hydroxyprogesterone; (3) hyperprolactinaemia — measure prolactin and assess for galactorrhoea; (4) thyroid dysfunction — check TSH; (5) androgen-secreting tumour — consider if virilisation is rapid or testosterone is markedly elevated; (6) Cushing's syndrome — consider if cushingoid features are present. The working diagnosis of PCOS is supported only after alternative causes have been reasonably excluded.

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Classifications & Scoring

SCORING TOOL

Modified Ferriman-Gallwey Score

Visual scoring system for hirsutism assessing terminal hair growth on nine body areas (upper lip, chin, chest, upper back, lower back, upper abdomen, lower abdomen, upper arm, thigh), each scored 0–4, with a total range of 0–36. A score ≥8 is commonly used to define hirsutism, though thresholds vary by ethnicity; the tool is the accepted standard for quantifying hirsutism in PCOS.

Clinical Calculator ↗

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Prognosis

SHORT-TERM OUTCOME

Short-term reproductive prognosis depends on the presenting phenotype and treatment goal. With lifestyle intervention and ovulation induction, many women achieve ovulation and pregnancy, although response rates vary with BMI and metabolic status. Menstrual regularity can be improved with combined oral contraceptives or cyclical progestogen. Cardiometabolic risk factors may already be present at diagnosis and require concurrent management.

LONG-TERM PROGNOSIS

PCOS is a lifelong condition with persistent metabolic and reproductive implications. In a 24-year follow-up, 19% of women with PCOS had developed type 2 diabetes versus 1% of controls. Endometrial cancer risk remains elevated, particularly with chronic anovulation and obesity. Cardiovascular risk-factor burden is increased, although evidence for an independent increase in cardiovascular mortality is inconsistent; long-term risk-factor surveillance and lifestyle management are central to care.

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References & Coding

ICD-10 DIAGNOSTIC CODE

E28.2

LITERATURE CITATIONS & GUIDELINES

[1]Rotterdam ESHRE/ASRM-Sponsored PCOS Consensus Workshop Group. Revised 2003 consensus on diagnostic criteria and long-term health risks related to polycystic ovary syndrome. Hum Reprod. 2004;19(1):41-47. doi:10.1093/humrep/deh098.

[2]Teede HJ, Tay CT, Laven J, et al. Recommendations from the 2023 International Evidence-based Guideline for the Assessment and Management of Polycystic Ovary Syndrome. Fertil Steril. 2023;120(4):767-793.

[3]Salari N, Nankali A, Ghanbari A, et al. Global prevalence of polycystic ovary syndrome in women worldwide: a comprehensive systematic review and meta-analysis. Arch Gynecol Obstet. 2024;310(3):1303-1314.

[4]SingHealth. Polycystic Ovary Syndrome (PCOS). Available at: https://www.singhealth.com.sg/symptoms-treatments/polycystic-ovary-syndrome. Accessed 2026.

[5]Yildiz BO, Bolour S, Woods K, Moore A, Azziz R. Visually scoring hirsutism. Hum Reprod Update. 2010;16(1):51-64.

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