Functional hypothalamic amenorrhoea: periods that stop with low energy

The menstrual cycle depends on a rhythm of signals from a region of the brain called the hypothalamus. When the body senses that fuel is scarce, it protects itself by switching down the reproductive system. Egg release stops, oestrogen falls and periods disappear. Nothing is wrong with the ovaries themselves, which is why they usually respond again when the brain restarts the signal.

This is different from premature ovarian insufficiency, where the ovaries are the problem and hormone tests show a high follicle-stimulating hormone. In FHA, the hormones that come from the brain are typically low or low-normal.

FHA is seen in athletes and dancers, in people who diet strictly or lose weight quickly, and in people with eating disorders. The NHS says anorexia nervosa can stop periods and lead to fertility problems and bone loss. It also occurs in people who are neither underweight nor in treatment for an eating disorder, when training load, restrictive eating and psychological stress add up.

Teenagers need particular attention, because periods that never start or stop early in adolescence can affect peak bone gain. The NHS advises seeing a GP if periods stop for three cycles in a row.

A GP will ask about eating, exercise, weight change, stress, medicines and other symptoms. A pregnancy test comes first. Blood tests commonly include thyroid function, prolactin, and the pituitary and ovarian hormones, and a pelvic scan may be arranged. If PCOS is suspected the picture can look similar on the surface, so careful interpretation matters.

Where the cause remains unclear or a pituitary problem is suspected, referral to an endocrinologist or gynaecologist follows, and imaging of the pituitary is sometimes needed. A bone density scan may be offered if periods have been absent for a long time.

• Pregnancy test.

• Thyroid function, prolactin, FSH, LH and oestradiol.

• Pelvic ultrasound.

• Bone density scan when amenorrhoea has lasted a long time.

• Pituitary imaging if hormone results or symptoms suggest it.

The core treatment is not a drug. It is raising energy intake, reducing training load where it is excessive, and addressing stress or eating-disorder behaviours. For people with anorexia nervosa the NHS describes talking therapies such as cognitive behavioural therapy and specialised approaches for adults, and family therapy for younger patients.

Support from a dietitian experienced in sport or eating disorders, a sports physician, and a psychologist is common. Small, steady changes tend to be more sustainable than abrupt ones, and the timeline to the first period varies from weeks to many months.

Taking the combined contraceptive pill gives a monthly bleed, but it does not reverse the underlying problem and the withdrawal bleed is not a true period. It has not been shown to rebuild bone in the way recovery of the natural cycle does. Clinicians may use oestrogen replacement in certain cases, such as in young people with delayed bone development, and the choice should be specialist-led. Calcium and vitamin D intake should be adequate.

Because ovulation has stopped, conception is unlikely until the cycle returns. Many people ovulate naturally once energy balance recovers. If they do not, a fertility specialist may offer ovulation induction with gonadotrophin treatment, which the NHS lists among its medicines for ovulation problems, although recovery first generally gives the healthiest start to pregnancy.

Pregnancy places high energy demands, so those who conceive while still underweight or restricting benefit from early antenatal support, as there are risks for both parent and baby.

Fainting, chest pain, a very slow pulse, or being unable to eat or drink needs urgent medical attention through 999, A&E or NHS 111. Anyone worried that their eating or exercise has become compulsive can see a GP without waiting for periods to stop.