34. Puberty and Delayed Puberty

First principle: reactivation of pulsatile GnRH, in sequence

• Thelarche = estrogen effect (usually the first sign).
• Pubarche = androgen effect — a different hormonal axis (adrenarche).
• Menarche follows breast development; early cycles are often anovulatory/irregular.

Two clinical levers this gives you

• Breast development = evidence of estrogen action — a single observation that powerfully narrows primary amenorrhoea (Concept 35).
• Because breast and hair run on different hormones, their dissociation separates look‑alikes (MRKH vs CAIS).

When to investigate delayed puberty

Discriminators (first split)

• No breasts + high FSH → gonadal failure (e.g. Turner).
• No breasts + low FSH → hypothalamic/pituitary (e.g. Kallmann, constitutional delay).

Pitfalls

• Using outdated age cut‑offs.
• Forgetting that constitutional delay (a normal variant, often familial) is the commonest cause of delayed puberty — but a diagnosis of exclusion.

Pearls

• 🎯 Thelarche→pubarche→growth→menarche; breasts = estrogen present. Investigate: no breasts by 13, no menarche by 15.
• 🩺 A short girl with delayed puberty and high FSH → check a karyotype for Turner.

Next → When menses never begin — a two‑question map (Concept 35).