Delayed Initiation of GnRH Antagonist Does Not Increase Premature Ovulation or Impair Oocyte and Embryo Quality in PCOS Patients Undergoing IVF: A Retrospective Cohort Study

Background: We aimed to evaluate whether delayed initiation of gonadotropin hormone-releasing hormone (GnRH) antagonist treatment affects premature ovulation and the number of good-quality blastocysts. We retrospectively reviewed the medical records of polycystic ovary syndrome (PCOS) patients who underwent in vitro fertilization (IVF) treatment at our clinic between 2017 and 2025. Patients were divided into two groups: Group 1: Patients in whom GnRH antagonist injections were initiated when at least three dominant follicles measured ≥17 mm. Group 2: Patients in whom GnRH antagonist injections were initiated when the leading follicle measured ≤14 mm. The groups were compared in terms of premature ovulation, estradiol (E ₂ ) level at GnRH antagonist initiation, total number of retrieved oocytes, number and proportion of metaphase II (MII) oocytes, fertilization rate, blastocyst number and rate, and good-quality blastocyst grades. Results: A total of 89 patients were included in the study. Of these, 38 patients were assigned to Group 1 and 51 to Group 2. here were no statistically significant differences in age or body-mass index (BMI) between the groups. Serum E ₂ levels at GnRH antagonist initiation were significantly higher in Group 1. The “median-(Interquartile Range (IQR))” total oocyte count was 33 (27–41) in Group 1 and 30 (26–40) in Group 2. The median 2PN count was 19.5 (12.75–27) in Group 1 and 19.0 (15–22) in Group 2. There were no statistically significant differences between the groups in terms of MII oocyte or two pronuclei (2PN) count. Blastocyst outcomes were comparable between the groups; the median number of day 5–6 blastocysts was 7.0 (5-11.5) in Group 1 and 8.0 (5–11) in Group 2. Furthermore, the median number of Grade A blastocysts was 4.0 (3–10) in Group 1 and 5.0 (min–max: 4–8) in Group 2, and there was no statistically significant difference between the groups regarding Grade‑A blastocyst counts. No premature ovulation occurred in either group. Conclusion: Delayed initiation of GnRH antagonist treatment in PCOS patients does not increase the risk of premature ovulation and does not impair oocyte or embryo quality.