Definition and epidemiology
Polycystic ovary syndrome (PCOS) is a heterogeneous endocrine disorder defined by a combination of ovulatory dysfunction, androgen excess, and polycystic ovarian morphology. It is sometimes informally referred to as a "polyendocrine metabolic ovarian syndrome" because it spans reproductive, metabolic, and endocrine axes simultaneously.
- Prevalence: approximately 6-12% of women of reproductive age, varying by diagnostic criteria used
- Most common cause of anovulatory infertility worldwide
- Onset typically around menarche, though diagnosis is often delayed until the late teens or twenties
- Strong association with obesity, though a lean phenotype (10-20% of cases) exists
- Familial clustering suggests a genetic component with polygenic inheritance
- Rotterdam criteria require 2 of 3: oligo/anovulation, hyperandrogenism, polycystic ovaries on ultrasound
- Elevated LH:FSH ratio (often >2:1) is classic but not required for diagnosis
- Insulin resistance is central to pathophysiology, independent of obesity
- First-line infertility treatment is letrozole, not clomiphene, per current guidelines
- Combined oral contraceptives are first-line for menstrual regulation and endometrial protection
- Chronic anovulation causes unopposed estrogen, raising endometrial hyperplasia/cancer risk
- Acanthosis nigricans is a cutaneous marker of underlying insulin resistance
- Must exclude non-classic CAH (17-OHP), hyperprolactinemia, and thyroid disease before diagnosing PCOS
Etiology and risk factors
The exact etiology is not fully understood, but PCOS is thought to arise from an interaction between genetic predisposition and environmental/metabolic factors.
- Genetic factors: polygenic inheritance; first-degree relatives have higher risk
- Insulin resistance: central to pathogenesis in most patients, independent of body mass index
- Obesity: amplifies insulin resistance and hyperandrogenism but is not required for diagnosis
- Intrauterine environment: prenatal androgen exposure theories have been proposed
- Risk factors: family history of PCOS or type 2 diabetes, obesity, sedentary lifestyle, premature adrenarche
Pathophysiology
PCOS pathophysiology centers on a self-reinforcing cycle involving the hypothalamic-pituitary-ovarian axis, ovarian androgen production, and peripheral insulin resistance.
Key mechanisms
- Increased GnRH pulse frequency leads to relatively increased LH secretion relative to FSH, raising the LH:FSH ratio
- Elevated LH stimulates ovarian theca cells to overproduce androgens (testosterone, androstenedione)
- Relatively low FSH impairs normal follicular maturation, causing follicular arrest and the classic "string of pearls" appearance
- Insulin resistance causes compensatory hyperinsulinemia; insulin acts synergistically with LH to further stimulate theca cell androgen production and suppresses hepatic sex hormone-binding globulin (SHBG), raising free testosterone
- Peripheral conversion of androgens to estrone in adipose tissue creates unopposed estrogen exposure on the endometrium, raising long-term endometrial hyperplasia/cancer risk
Clinical features
Presentation is variable, reflecting the syndrome's heterogeneity.
- Menstrual irregularity: oligomenorrhea or amenorrhea due to chronic anovulation
- Hyperandrogenism: hirsutism (terminal hair in male-pattern distribution), acne, androgenic alopecia
- Infertility: due to chronic anovulation
- Obesity: often central/abdominal, present in a majority but not all patients
- Acanthosis nigricans: velvety hyperpigmented skin at neck/axillae, marker of insulin resistance
- Metabolic features: dyslipidemia, impaired glucose tolerance, higher risk of metabolic syndrome
- Psychiatric: increased rates of anxiety, depression, and body image concerns
Diagnosis
PCOS is a clinical diagnosis of exclusion, most commonly made using the Rotterdam criteria (ESHRE/ASRM), requiring at least 2 of the following 3 after excluding other etiologies:
- Oligo-ovulation or anovulation
- Clinical (hirsutism, acne) and/or biochemical hyperandrogenism (elevated free testosterone)
- Polycystic ovaries on transvaginal ultrasound (12 or more follicles 2-9mm, and/or increased ovarian volume)
Workup
- Hormonal panel: total/free testosterone, LH, FSH (LH:FSH ratio often >2:1, not required for diagnosis), TSH, prolactin
- Exclude mimics: 17-hydroxyprogesterone (congenital adrenal hyperplasia), prolactin (hyperprolactinemia), TSH (thyroid disease), DHEAS and imaging if virilization is rapid or severe (androgen-secreting tumor)
- Metabolic screening: fasting glucose/HbA1c or oral glucose tolerance test, lipid panel, given high association with insulin resistance
- Pelvic ultrasound: transvaginal preferred, assesses follicle count and ovarian volume
Other diagnostic frameworks (NIH criteria, Androgen Excess Society criteria) exist and differ slightly in required features; Rotterdam is the most widely used internationally.
Differential diagnosis
| Condition | Distinguishing feature |
|---|---|
| Congenital adrenal hyperplasia (non-classic) | Elevated 17-hydroxyprogesterone, often earlier/more severe virilization |
| Hyperprolactinemia | Elevated prolactin, possible galactorrhea |
| Thyroid dysfunction | Abnormal TSH, other systemic thyroid symptoms |
| Androgen-secreting tumor (ovarian/adrenal) | Rapid-onset severe virilization, very high testosterone/DHEAS |
| Cushing syndrome | Central obesity, striae, hypertension, elevated cortisol |
| Hypothalamic amenorrhea | Low gonadotropins, low estrogen, often low body weight/excess exercise |
Management
Management is individualized based on the patient's primary concern: menstrual irregularity, hyperandrogenism, infertility, or metabolic risk. There is broad consensus (ESHRE, Endocrine Society, ACOG) that lifestyle modification is first-line for all phenotypes.
General and metabolic
- Lifestyle modification: weight loss (even 5-10% body weight) improves ovulation, insulin sensitivity, and hyperandrogenism; first-line in overweight/obese patients
- Metformin: improves insulin sensitivity; used for metabolic features and sometimes to aid ovulation, particularly in combination with lifestyle change or clomiphene
Menstrual irregularity / endometrial protection
- Combined oral contraceptives: first-line for regulating cycles, treating hirsutism/acne, and protecting the endometrium from unopposed estrogen exposure
- Cyclic progestins as an alternative if estrogen is contraindicated
Infertility (ovulation induction)
- Letrozole: first-line ovulation induction agent per current guidelines (superior live birth rates compared with clomiphene in several trials)
- Clomiphene citrate: alternative ovulation induction agent
- Gonadotropins or laparoscopic ovarian drilling: second-line if oral agents fail
- In vitro fertilization: reserved for refractory cases
Hirsutism/acne
- Combined oral contraceptives first-line
- Spironolactone or other anti-androgens added if inadequate response (contraindicated without reliable contraception due to teratogenicity risk)
- Topical eflornithine, cosmetic hair removal as adjuncts
Guideline note: international guidelines agree on lifestyle and combined oral contraceptives as first steps; some variability exists regarding timing/threshold for adding metformin or anti-androgens.
Complications and prognosis
PCOS is a chronic condition with lifelong metabolic and reproductive implications, though symptoms and risks can be substantially managed.
- Type 2 diabetes mellitus: significantly increased lifetime risk due to underlying insulin resistance
- Metabolic syndrome and cardiovascular risk: dyslipidemia, hypertension, increased cardiovascular risk factors
- Endometrial hyperplasia and endometrial cancer: from chronic unopposed estrogen exposure due to anovulation
- Infertility and pregnancy complications: increased risk of gestational diabetes, pregnancy-induced hypertension, and miscarriage
- Obstructive sleep apnea: more common than in the general population
- Psychological impact: higher rates of anxiety and depression
Prognosis is generally favorable with long-term management; fertility can often be achieved with ovulation induction, and metabolic risks can be mitigated through sustained lifestyle intervention and surveillance.
PCOS = "ABCD": Anovulation, Biochemical/clinical hyperandrogenism, Cysts (polycystic ovaries), Diabetes risk (insulin resistance)
Practice questions
1. A 22-year-old woman presents with irregular menses since menarche, facial acne, and hirsutism. BMI is 29. Pelvic ultrasound shows 14 small follicles in each ovary. Serum 17-hydroxyprogesterone, prolactin, and TSH are normal. Which of the following best supports the diagnosis?
2. A 28-year-old woman with PCOS and a BMI of 32 wishes to conceive. She has tried lifestyle modification for 6 months without success. Her partner's semen analysis is normal and her fallopian tubes are patent. Which medication is the most appropriate first-line agent for ovulation induction?
3. A 35-year-old woman with longstanding PCOS and chronic oligomenorrhea has not been on hormonal therapy for several years. She now presents with intermenstrual bleeding. Which of the following is the most important long-term risk this presentation raises concern for?
Frequently asked questions
What causes PCOS?
PCOS results from a combination of genetic predisposition and insulin resistance that disrupts the hypothalamic-pituitary-ovarian axis. Increased LH relative to FSH drives ovarian androgen overproduction, while hyperinsulinemia worsens hyperandrogenism and lowers sex hormone-binding globulin. The exact cause isn't fully known, but family history and obesity are major contributing risk factors.
What are the first symptoms of PCOS?
The earliest signs are usually irregular or absent menstrual periods beginning around menarche, along with hirsutism (excess facial/body hair) and acne. Weight gain, particularly central obesity, and darkened velvety skin patches (acanthosis nigricans) at the neck or armpits may also appear early. Not all women show every feature, and severity varies widely.
How is PCOS diagnosed?
PCOS is diagnosed clinically using the Rotterdam criteria, requiring at least two of three features: irregular ovulation, signs of excess androgens (clinical or on blood tests), and polycystic ovaries on ultrasound. Other causes of these findings, such as thyroid disease, high prolactin, or congenital adrenal hyperplasia, must be ruled out with blood tests first.
Is PCOS curable?
PCOS is not curable, but it is highly manageable. Lifestyle changes, hormonal therapy, and medications targeting insulin resistance or fertility can effectively control symptoms, regulate cycles, and improve chances of pregnancy. Long-term management focuses on reducing metabolic and reproductive complications rather than achieving a cure.
PCOS vs congenital adrenal hyperplasia — what is the difference?
Both cause hyperandrogenism, but non-classic congenital adrenal hyperplasia is caused by an enzyme deficiency (usually 21-hydroxylase) and is confirmed by an elevated 17-hydroxyprogesterone level, often with earlier or more severe virilization. PCOS has normal 17-hydroxyprogesterone and is diagnosed by Rotterdam criteria after excluding CAH and other causes.
Key drugs
Related conditions and differentials
Sources and further reading
StatPearls (NCBI Bookshelf)MedlinePlusWHO ICD-10: E28.2
Educational content for medical students, prepared by the WhiteCoat Pro editorial team with AI assistance; every page is reviewed by a second AI model for factual errors. It is not medical advice and does not replace the product label, local guidelines or a clinician.