The normal menstrual cycle & HPO axis — structured oral station (12 minutes)

Opening prompt — "Talk me through the physiology that has gone wrong here."

Model response — sequence it from the axis up: ^[1][2]

• "This is a hypogonadotropic state. Her energy deficit has silenced the hypothalamic GnRH pulse generator, so FSH and LH fall, the ovary is not driven, and oestradiol is low — the endometrium sees no oestrogen and does not proliferate, so she stops bleeding."
• "To make oestradiol you need both gonadotrophins: LH on theca cells makes the androgens, FSH on granulosa cells aromatises them — the two-cell two-gonadotrophin theory. With both suppressed, that cooperation stalls."^[1]

Probe 1 — "How does that compare with PCOS and with premature ovarian insufficiency?"

• "I classify anovulation by the gonadotrophin profile. Low FSH/LH and low oestradiol is hypothalamic or pituitary — her picture. Normal gonadotrophins with disordered feedback is PCOS. High FSH with low oestradiol is a failing ovary — premature ovarian insufficiency."^[3][4]

Probe 2 — "Her day-3 bloods confirm low FSH, low LH, low oestradiol. What else must you check before concluding it is functional?"

• "Pregnancy first — always. Then thyroid function and prolactin, which both suppress the GnRH pulse generator and mimic functional hypothalamic amenorrhoea. I would also screen for an eating disorder and assess her training and intake."^[3]

Probe 3 — "How would you confirm whether she ovulates once cycles return?"

• "The single best test is a midluteal serum progesterone — about day 21 of a 28-day cycle, or 7 days before her expected menses. A value in the ovulatory range proves a corpus luteum. I would not rely on a single random hormone level, and anti-Müllerian hormone measures reserve, not ovulation."^[1]

Probe 4 — "She is distressed about her fertility. What do you say?"

This is a scored communication domain — demonstrate it out loud: ^[1]

• Move to her eye level, use her name, acknowledge the fear: "Your fertility is at risk right now because your body is protecting itself — when energy is scarce, reproduction switches off. The good news is that this is usually reversible, and the first step is not a drug, it is restoring your energy balance."
• Be honest that ovulation induction is possible later but that restoring cycles naturally, and protecting her bones with oestrogen if needed, comes first. Offer dietetic and psychological support and a follow-up plan.^[3]

Probe 5 — "What is the risk if she does nothing?"

• "Chronic hypo-oestrogenism loses bone — she is accumulating osteoporosis silently — and carries cardiovascular and sexual-health morbidity. Reassurance without action is not safe. I would also counsel her on adequate energy intake relative to her training."^[3]