The normal menstrual cycle & HPO axis — structured SAQ (15 marks)

(a) Classify the level of axis failure (4 marks)

One mark per point, maximum four. ^[1][4]

• Hypogonadotropic hypogonadism — an energy deficit from training and dietary restriction has silenced the GnRH pulse generator, so FSH, LH and oestradiol are all low.^[3][4]
• Expected day-3 pattern: low FSH, low LH, low oestradiol — the hypothalamic/pituitary level.^[1]
• Contrast the profile to localise: low = hypothalamus/pituitary; normal = PCOS; high (FSH) = premature ovarian insufficiency.^[4][5]
• Exclude mimics before concluding: pregnancy (always), thyroid disease, hyperprolactinaemia.^[3]

(b) Two-cell two-gonadotrophin theory (4 marks)

One mark per point. ^[1]

• LH receptors are on theca cells, where LH drives androgen (androstenedione) synthesis.
• FSH receptors are on granulosa cells, where FSH induces aromatase, converting theca-derived androgens to oestrone and then oestradiol.
• Oestradiol synthesis therefore needs both cell types and both gonadotrophins.^[1]
• This woman is hypo-oestrogenic because her FSH and LH are suppressed (no GnRH pulses), so neither theca nor granulosa are driven — the two-cell cooperation stalls and the follicle cannot make the oestradiol needed for the endometrium.^[1][3]

(c) Confirming ovulation (3 marks)

One mark per point. ^[1][2]

• The single best test of ovulation is a midluteal serum progesterone (about day 21 of a 28-day cycle, or 7 days before the expected next menses).
• A value in the ovulatory range confirms a functioning corpus luteum.
• In an amenorrhoeic woman, ovulation cannot be timed this way; the first objective is to restore cycles, then confirm ovulation with a midluteal progesterone in a subsequent cycle.^[1]

(d) Restoring the axis and the risk of non-treatment (4 marks)

One mark per point. ^[3][4]

• First-line is restoring energy availability — nutrition, weight restoration, reducing training intensity — because the lesion is functional, not structural.
• If cycles do not return, evaluate for other causes and consider oestrogen replacement.
• Oestrogen replacement protects bone and cardiovascular health in the woman not seeking pregnancy.^[3]
• Risk of leaving it untreated: progressive bone loss (and cardiovascular/sexual-health morbidity) from chronic hypo-oestrogenism; reassurance without action is not safe.^[3]