The simple idea (no memorising)
Pregnancy is by far the commonest cause of periods stopping. Once it's excluded, run a simple panel — TSH (thyroid), prolactin, and FSH — and sort by the answers:
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The main causes (each with a fingerprint)
- PCOS — the commonest pathological cause: irregular cycles, hair, acne (Part 3).
- High prolactin (prolactinoma) — a pituitary tumour raising prolactin, which switches off the axis → amenorrhoea, sometimes milky discharge (galactorrhoea), headache or visual changes. (Note: no galactorrhoea does not rule it out.) Treated with dopamine‑agonist tablets.
- Thyroid disease — over‑ or under‑active thyroid disturbs ovulation; that's why TSH is checked even without obvious symptoms.
- Sheehan syndrome — after a major postpartum haemorrhage, the pituitary is starved of blood and fails → can't breastfeed + periods never return. The obstetric story is the clue. 🚩
- Functional hypothalamic amenorrhoea (FHA) — from low energy, heavy exercise, big weight loss or stress; the brain dials down GnRH to conserve energy. The fix is restoring energy balance, not just forcing a bleed with a pill.
- Primary ovarian insufficiency (POI) — the ovary failing early → high FSH, like an early menopause.
- Asherman syndrome — scarred, stuck‑together lining after a uterine procedure or TB (Concept 28).
The master shortcut: let FSH point the finger
- FSH high → the ovary has failed (it's not answering, so the brain shouts louder). e.g. POI, Turner.
- FSH low or normal with low estrogen → the brain/pituitary isn't signalling. e.g. Kallmann, FHA.
Why it matters
This calm sequence — pregnancy → TSH/prolactin/FSH → localise — solves an enormous range of cases and prevents dangerous misses (like an unrecognised pregnancy or pituitary tumour).
Quick check ✅
- What is the very first test in secondary amenorrhoea?
- A woman had a major postpartum bleed, then couldn't breastfeed and her periods never came back. Diagnosis?
Remember this 🌟
Where we're going next → Our final part looks at the three gynaecological cancers — and how understanding hormones makes them click. Concept 37.