Final oocyte maturation for in vitro fertilization: a comprehensive review with investigators’ recommendations

The use of gonadotropin-releasing hormone (GnRH) antagonist protocols in assisted reproductive technology provides various options for achieving final follicular maturation. The choice of agent should be tailored to the patient characteristics and the mechanism of action of the triggers. The two primary agents used for this purpose are human chorionic gonadotropin, which acts as a luteinizing hormone analogue, and GnRH agonist, which induces the release of internal gonadotropin stores. Although these agents aim to achieve the same goal, they differ in the mechanism of action and downstream effects. Human chorionic gonadotropin binds to the luteinizing hormone receptors in the ovarian follicles and promotes oocyte maturation and ovulation through continuous luteotropic activity. This prolonged effect can increase the risk of ovarian hyperstimulation syndrome. GnRH agonists trigger ovulation by stimulating an endogenous gonadotropin surge. This process more closely resembles natural ovulation but is transient because of the short half-life. Another option is the dual trigger approach, when human chorionic gonadotropin is combined with GnRH agonist with the aim to optimize oocyte maturation while balancing safety and efficacy. Understanding the underlying mode of action of the triggers is crucial for tailoring individualized treatment protocols, achieving optimal oocyte yield and quality, enhancing clinical outcomes while appropriately mitigating the risks. With this manuscript, we aim to provide an in-depth review of each ovulation trigger agent and their combination and summarize recommendations on the basis of the most common patient characteristics.