What is commonly used as a trigger for final oocyte maturation?

• A. Progesterone administration
• B. GnRH antagonist administration
• C. hCG trigger for final oocyte maturation
• D. No trigger

Answer: (C)

Final oocyte maturation is driven by a surge in LH-like activity. In assisted reproduction, the common way to induce this maturation is an injection of human chorionic gonadotropin. hCG acts on LH receptors in the dominant follicle, prompting the oocyte to resume meiosis, promoting cumulus expansion, and triggering ovulation-like events so retrieval can occur at the optimal time (about 34–36 hours later). The reason hCG is favored is its LH-like effect lasts longer than the body's natural LH surge, providing a robust and reliable maturation signal and a predictable timing window for oocyte collection. Progesterone administration does not initiate maturation; it is mainly used for luteal-phase support after retrieval. A GnRH antagonist is used during stimulation to prevent an premature LH surge, not to trigger maturation. (In some protocols, a GnRH agonist can be used as a trigger in antagonist cycles to reduce OHSS risk, but the traditional and most common trigger remains hCG.)