Determination of the optimal follicle size at the time of trigger in patients with diminished ovarian reserve undergoing ICSI cycle

Patients with diminished ovarian reserve (DOR) typically have fewer retrieved oocytes and lower pregnancy rates than normal responders. Therefore, maximizing oocyte yield is particularly important to improve their reproductive outcomes. The purpose of this study was to improve reproductive outcomes in assisted reproductive technology (ART) by determining the optimal follicle size to induce final oocyte maturation in patients with DOR. A total of 430 follicles from 98 DOR patients were included in this study. Controlled ovarian stimulation was conducted by a GnRH antagonist protocol, with ovulation triggered when the leading follicle reached ≥ 17 mm, followed by oocyte retrieval 36 h later. On the day of oocyte retrieval, in the operating theatre, all follicles were carefully measured, one by one, by a second trained individual just before aspiration. Then, each follicle was aspirated separately and collected in a separate tube. Throughout the laboratory process, oocytes were tracked and managed based on the size of the follicle from which they originated. Based on follicle size, 11–14 mm, 15–17 mm, and ≥ 18 mm, the follicles were divided into three groups. Reproductive outcomes in this study were included Cumulus Oocyte Complex (COC) retrieval rate, metaphase II (MII) oocyte rate, fertilization rate, and top-quality embryo (TQE) rate. The final analysis included a total of 430 follicles were measured and aspirated. Follicles measuring 15–17 mm exhibited a significantly higher COC retrieval rate (88.1%), MII oocyte rate (83.3%), fertilization rate (97.1%), and TQE rate (65.4%), in comparison to follicles measuring 11–14 mm and ≥ 18 mm (p < 0.05). The COC retrieval rate and the MII retrieval rate were 79.16% and 66.66%, for follicles measuring 14 mm, and were 45.09% and 33.33%, for follicles measuring 13 mm, respectively (p < 0.05). ROC analysis identified an optimal follicle size of 14.5–15.5 mm for COC retrieval. The incidence of premature ovulation was 13.27% and the mean size of the leading follicle on the day of trigger was 18.6 mm in patients with premature ovulation. Our study suggests that oocyte retrieval, maturation and embryo development are optimized by triggering final oocyte maturation at a follicle size of 15–17 mm. In addition, there is a need to reconsider the standard trigger criteria in these patients.