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: low energy availability (LEA – intake too low for energy expended, whether from dieting, an eating disorder, or heavy training), excessive exercise, and psychological stress, often in combination. 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 – and 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 single most important 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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