The association between treatment parameters on the day of gonadotropin-releasing hormone antagonist initiation during a flexible protocol and oocyte maturation rate.

This study aimed to evaluate the effects of different treatment parameters on the day of GnRH antagonist initiation on oocyte maturation rate. We performed a retrospective cohort study of women aged ≤ 38 who underwent their first IVF-ICSI treatment using a flexible GnRH antagonist protocol in a single university-affiliated medical center during 2005-2015. Treatment parameters of three groups of oocyte maturation rates (<60%, 60-90%,>90%) were compared. Multivariate analysis was conducted to detect an association between treatment parameters on the day of GnRH antagonist initiation and oocyte maturation rate. The cohort included 458 patients, of whom 180 (39%) had a high oocyte maturation rate (≥90%), 211 (46%) had an oocyte maturation rate between 60-90% and 67 (15%) had a low maturation rate (≤60%). Women with a high maturation rate had longer duration of treatment (10.3 ± 2.9 days vs. 9.6 ± 2.5 vs. 9.5 ± 3.2, P = 0.019), lower levels of estradiol (1985 ± 1357 vs. 2406 ± 1666 vs. 2325 ± 1811, P = 0.027) and lower estradiol/maximal follicular diameter ratio on the day of GnRH antagonist initiation (137 ± 89 vs. 165 ± 103 vs. 163 ± 125, P = 0.019) as compared to women with medium and low maturation rates, respectively. Using linear regression multivariate analysis, lower estradiol and lower estradiol/maximal follicular diameter ratio on GnRH antagonist initiation day were associated with higher oocyte maturation rate. Further prospective studies to determine the best timing for GnRH antagonist initiation are needed.