Optimal timing for triggering oocyte maturation during in vitro fertilization cycles varies between gonadotropin-releasing hormone agonist and human chorionic gonadotropin use.

Objective: To investigate the optimal timing for triggering oocyte maturation by evaluating the interval from the trigger to oocyte retrieval and the subsequent in vitro fertilization outcomes. The administration of human chorionic gonadotropin (hCG) or gonadotropin-releasing hormone agonist (GnRHa) is a critical trigger for the final maturation of oocytes within in vitro fertilization cycles. The interval between the trigger and oocyte retrieval has typically been set at 34-40 hours. However, the best timing on the basis of the type of trigger is still unclear. Design: A single-center retrospective cohort study. Subjects: A total of 59,206 oocyte retrieval cycles were investigated at our clinic between April 2010 and March 2024. Cycles with luteinizing hormone surge and those undergoing oocyte retrieval on the day after the trigger were excluded. Exposure: The interval from trigger to oocyte retrieval was from GnRHa or hCG administration to oocyte retrieval initiation. The subjects were categorized into the following two groups according to the type of oocyte maturation trigger used: GnRHa group (buserelin [600 μg] nasal spray) and hCG group (hCG [3,000-10,000 IU] or choriogonadotropin alfa [250 μg] subcutaneously). Main Outcome Measures: The primary outcome measure was the total number of mature metaphase II (MII) oocytes retrieved. Results: The GnRHa trigger group had a higher number of MII oocytes retrieved with a longer interval than with a shorter interval (7.2 ± 6.5 vs. 4.3 ± 5.3), whereas the hCG trigger group had fewer oocytes with a longer interval than with a shorter interval (4.0 ± 4.6 vs. 6.9 ± 5.8). The differences between shorter and longer intervals became more pronounced in older age groups. Although the MII ratio per oocyte did not show significant difference with the interval duration, the blastocyst formation rate and total number of blastocysts were markedly higher when the interval was longer than 36.5 hours in the GnRHa group. Conclusion: The optimal interval varies between the GnRHa trigger and the hCG trigger, with the hCG trigger associated with a shorter interval for obtaining the maximum number of MII oocytes than the GnRHa trigger.