GPAtlas🧭 When to suspect
Functional hypothalamic amenorrhoea (FHA) is the cessation of periods caused by a functional suppression of the hypothalamic–pituitary–ovarian (HPO) axis, with no structural or organic cause.
Reduced pulsatile secretion of gonadotrophin-releasing hormone (GnRH) lowers luteinising hormone (LH) and follicle-stimulating hormone (FSH), which in turn drops oestradiol and stops ovulation.
It is best understood as the body’s protective adaptation to a perceived energy or stress threat, and it accounts for roughly one third of secondary amenorrhoea in women of reproductive age.
Suspect FHA in a woman with secondary amenorrhoea – absence of periods for 3–6 months after previously regular cycles (or 6–12 months if previously oligomenorrhoeic) – in the setting of the classic triad, often in combination:
• Low energy availability (LEA – intake too low for energy expended, whether from dieting, an eating disorder, or heavy training)
• Excessive exercise
• Psychological stress
In athletes and dancers this sits within Relative Energy Deficiency in Sport (RED-S), the modern framework that replaced the older “female athlete triad” of low energy availability, menstrual dysfunction, and low bone density.
Two skills matter most in primary care:
• Confirm FHA only by exclusion – it is never a first-line label.
• Recognise that the real danger is the chronic low-oestrogen state, principally its effect on bone.
The reassuring counterpoint is that FHA is usually reversible: restoring energy balance restores the cycle.
| Cause to exclude first | Pointers |
|---|---|
| Pregnancy | The first step in any woman with amenorrhoea – always do a urine hCG (human chorionic gonadotrophin) before anything else. |
| Hyperprolactinaemia | • Galactorrhoea, headache or visual change • Drug causes (antipsychotics, metoclopramide) • Raised prolactin |
| Thyroid disease | • Weight, temperature or bowel change, goitre • Abnormal TSH (thyroid-stimulating hormone) |
| Polycystic ovary syndrome (PCOS) | • Oligomenorrhoea, hirsutism or acne, often higher body mass index (BMI) • Raised free androgens |
| Premature ovarian insufficiency (POI) | • Under 40 with hot flushes, night sweats, vaginal dryness • Raised FSH and LH on two occasions |
| Uterine/outflow (e.g. Asherman’s) | • Previous uterine surgery or instrumentation • Normal hormone profile with absent bleeding |
| Functional hypothalamic amenorrhoea | • Low energy availability, weight loss, excessive exercise or stress • Low or low-normal LH and FSH with low oestradiol – the diagnosis that remains once the above are excluded |
|
⚠️ Common pitfall • Confusing FHA with PCOS – both cause oligo/amenorrhoea, but they pull in opposite directions and so does their management. • FHA typically shows a low or normal BMI, low androgens, and low gonadotrophins. • PCOS more often shows a higher BMI, clinical or biochemical hyperandrogenism, and a raised LH. • Labelling an underweight, over-training woman as “PCOS” risks missing a treatable energy deficit and progressive bone loss. |
Source: Endocrine Society · RED-S consensus (BASEM/IOC)
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