How do GnRH agonist and antagonist protocols differ in IVF?

• A. GnRH agonists cause immediate suppression of gonadotropins, while antagonists require a lead-in period.
• B. Both phases rely on suppression of LH from the start.
• C. GnRH agonists cause an initial flare of gonadotropins followed by suppression; antagonists provide immediate suppression to prevent a premature LH surge.
• D. GnRH agonists and antagonists have no effect on LH during stimulation.

Answer: (C)

The key idea is controlling the pituitary LH surge to time ovulation during ovarian stimulation. GnRH agonists work by first briefly stimulating the pituitary, causing a surge of LH and FSH (flare) before they desensitize the receptors and suppress endogenous gonadotropin production. This requires a lead‑in downregulation phase before starting exogenous gonadotropins, so follicular growth is driven in a more controlled, often longer protocol.

GnRH antagonists, on the other hand, block GnRH receptors immediately, so there is no flare and LH is suppressed right away as stimulation begins. An antagonist is added when there’s a risk of a premature LH surge (usually once follicles reach a certain size), allowing a shorter, more flexible cycle without prior downregulation.