Polycystic ovary syndrome
Insulin resistance drives compensatory hyperinsulinaemia that pushes the ovary to overproduce androgens and arrests follicle development, producing the combination of hyperandrogenism, anovulation and polycystic ovaries.
In a nutshell
Insulin resistance causes compensatory hyperinsulinaemia, which drives ovarian theca cells to overproduce androgens and suppresses hepatic SHBG, raising free androgen. Excess androgens and disturbed LH signalling arrest follicle development before ovulation, producing anovulation, hyperandrogenism and the polycystic ovarian appearance.
Classic presentation
Oligomenorrhoea or amenorrhoea with hirsutism, acne and subfertility, often in a woman with obesity or other features of insulin resistance.
Key points
- Diagnosis needs 2 of 3 Rotterdam criteria: oligo/anovulation, clinical or biochemical hyperandrogenism, polycystic ovaries on ultrasound.
- Hyperinsulinaemia lowers SHBG, so free androgen can be raised even when total testosterone looks only mildly abnormal.
- The polycystic ovary appearance reflects arrested antral follicles, not true cysts.
- Chronic anovulation causes unopposed oestrogen exposure, raising endometrial hyperplasia risk if untreated.
- Weight loss directly improves insulin sensitivity and can restore ovulation: it targets the root cause, not just symptoms.
- Letrozole is now generally preferred over clomifene for ovulation induction in PCOS-related subfertility.
First-line investigation
Pelvic ultrasound plus serum testosterone and SHBG (free androgen index), alongside LH/FSH, prolactin and TFTs to exclude other causes.
First-line management
Weight loss and lifestyle change as the foundation; COCP for cycle regulation and endometrial protection, ovulation induction agents for those seeking fertility.
Exam traps
- Polycystic ovaries on ultrasound alone, without oligo/anovulation or hyperandrogenism, do not make the diagnosis of PCOS.
- Rapid-onset severe virilisation is not typical PCOS and should prompt investigation for an androgen-secreting tumour.
- LH:FSH ratio is a classically taught but not required Rotterdam criterion: do not rely on it alone to diagnose or exclude PCOS.
Educational content pending clinical review. Not medical advice.