Optimal leading follicle size for final oocyte maturation in POSEIDON group 3 and 4 poor responders undergoing assisted reproductive technology cycles.

Objective: The aim of this retrospective cohort study was to evaluate the relationship between leading follicle size at the time of human chorionic gonadotropin (hCG) trigger and live birth rates in Patient-Oriented Strategies Encompassing Individualised Oocyte Number (POSEIDON) groups 3 and 4 undergoing assisted reproductive technology cycles using a gonadotropin releasing hormone (GnRH) antagonist protocol. The objective was to identify the optimal leading follicle size for maximizing live birth outcomes in this challenging patient population.

Material and methods: This retrospective cohort study included POSEIDON groups 3 and 4 poor responders aged 20-42 years undergoing intracytoplasmic sperm injection with GnRH antagonist protocol between January 2015 and July 2021. Patients were categorized based on the occurrence of premature ovulation. The primary outcome measures were number of oocytes retrieved, number of metaphase II (MII) oocytes, MII oocyte ratio and follicle oocyte index (FOI). These outcomes were compared across different leading follicle size categories at the time of hCG trigger.

Results: Among the 294 subjects included, 47 (16.2%) had premature ovulation between the trigger and oocyte pick-up days. The mean size of the leading follicle on the day of trigger was significantly higher in the premature ovulation group (19.8±2.4 mm vs.18.7±2 mm, respectively; p<0.001). Multivariate logistic regression analyses identified baseline luteinizing hormone [odds ratio (OR) 1.144, 95% confidence interval (CI) 1.052-1.243; p=0.002], number of follicles >11 mm on the day of trigger (OR 0.580, 95% CI 0.438-0.767; p<0.001), and leading follicle size (OR 1.361, 95% CI 1.130-1.641; p=0.001) as independent predictors of premature ovulation. The FOI and MII/antral follicle count ratios peaked when the leading follicle size was between 16-17 mm.

Conclusion: Individualized triggering based on leading follicle size may provide optimal oocyte retrieval after ovarian stimulation in POSEIDON expected poor responders. While a late trigger may result in premature ovulation, an early trigger may also result in less MII. Triggering when the leading follicle size is between 16.5 and 17 mm may help to prevent these negative outcomes and achieve optimal cycle outcome.