Synopsis
Approach absent menstruation from pregnancy and anatomy through ovarian and hypothalamic-pituitary physiology, identify urgent endocrine disease, and protect bone, endometrium and fertility while treating the cause.
- Exclude pregnancy first in every person with pregnancy potential, regardless of stated infertility, contraception, sexual orientation or cycle irregularity.
- Primary amenorrhoea concerns menstruation that has not begun by the age or pubertal stage in current guidance; secondary amenorrhoea is loss of established bleeding for a clinically significant interval.
- The presence of breasts, uterus, cervix and androgen signs directs primary amenorrhoea assessment before a long laboratory list is ordered.
- High FSH with low oestrogen indicates ovarian insufficiency, while low or inappropriately normal FSH and LH suggests hypothalamic-pituitary suppression or failure.
- Functional hypothalamic amenorrhoea is caused by low energy availability, excessive exercise, stress or illness after alternative causes are excluded; a normal BMI does not exclude it.
- Raised prolactin may reflect pregnancy, medicines, stress, renal disease, macroprolactin or a pituitary lesion; confirm appropriately before imaging unless mass symptoms demand urgency.
- Hyperandrogenism with irregular cycles commonly suggests PCOS, but rapid virilisation, severe testosterone elevation and Cushing features require a different pathway.
- Amenorrhoea on hormonal contraception may be an expected medicine effect, but new pregnancy symptoms, pain or systemic endocrine features still require assessment.
- Management is cause specific and must protect bone during hypo-oestrogenism and endometrium during chronic anovulation, while discussing contraception and fertility explicitly.
Key red flags
Galactorrhoea, low libido, headache or visual change with suppressed gonadotrophins suggests prolactin excess, although galactorrhoea may be absent and medicine causes are common.
Normal breast development with absent uterus suggests Müllerian agenesis or androgen insensitivity, while cyclic pain with retained blood suggests outflow obstruction requiring gynaecological assessment.
Rapid hair change, deep voice, clitoromegaly or marked testosterone abnormality suggests an ovarian or adrenal source rather than uncomplicated PCOS.
Acute headache, ophthalmoplegia, visual loss, collapse, vomiting or severe postural hypotension can indicate apoplexy or cortisol deficiency and needs immediate treatment.
Investigation priorities
Exclude pregnancy before endocrine testing, imaging choices or hormone treatment.
Management branches
Previously established menstruation has stopped beyond the current clinical threshold.
- Test for pregnancy and assess pain, bleeding, haemodynamic symptoms, contraception, lactation, medicines, weight or intake change, exercise, stress and chronic illness.
- Examine blood pressure, thyroid, galactorrhoea, androgen and Cushing features and signs of energy deficiency, using trauma-informed discussion of eating and pregnancy possibility.
- Measure FSH, LH, oestradiol, prolactin and thyroid function, adding androgen or adrenal tests when the phenotype supports them.
- Direct care to POI, functional hypothalamic, PCOS, prolactin, thyroid or structural pathways and plan bone or endometrial protection while definitive treatment proceeds.