The Association between Treatment Parameters on the Day of Initiation of Gonadotropin-Releasing Hormone Antagonist in Flexible IVF Protocol and Oocyte Maturation Rate

Introduction: GnRH antagonist initiation in GnRH antagonist protocols is scheduled either on the sixed day of ovarian stimulation (fixed protocol) or according to the maximal follicle diameter (flexible protocol). Treatment outcomes in both regimens are comparable.

Aim: To evaluate treatment parameters that may affect oocyte maturation rate in GnRH antagonist cycles.

Materials and methods: A retrospective cohort study of women aged ≤38 who underwent their first IVF treatment using a flexible GnRH antagonist protocol. Treatment parameters of cycles with high oocyte maturation rate (≥80%) were compared to cycles with low maturation rate (<80%).

Results: The cohort included 462 patients; 236 patients (51%) had a high oocyte maturation rate. Compared to women with low maturation rate, women with high maturation rate had higher gravidity and parity, higher progesterone level on the trigger day, greater number of high quality embryos and frozen embryos, and lower number of retrieved oocytes (12.80±7.2 vs. 14.07±7.3, P=0.005). Regarding treatment parameters on the day of initiation of GnRH antagonist, women in the high maturation group had lower levels of estradiol (2064±1323 vs. 2403±1796, P=0.007), lower estradiol/ maximal follicle diameter ratio (142±85 vs. 165±115, P=0.012), and longer duration of treatment with GnRH antagonist (5.2±1.8 vs. 4.6±2.1 days, p=0.003) compared to women with low maturation rate, respectively.

Conclusions: In GnRH antagonist cycles, higher oocyte maturation rate was found when initiation of the antagonist treatment occurred at lower estradiol levels, lower estradiol/ maximal follicle diameter ratio, and longer duration of treatment with GnRH antagonist, possibly reflecting enhanced follicular synchronization.