GnRH Antagonist Pre-treatment for the Prevention of Asynchronous Follicular Growth

In the study the investigators would like to examine the effect of GnRH antagonist administration at the beginning of the follicular phase in patients presenting with high baseline estradiol levels of 200 pmol/L or above with a leading follicle of 11-13 mm. In the unit's practice, patients presenting for cycle initiation with a leading follicle \> 10 in the presence of E2 \> 200 pmol/L (54 pg/ml) are deferred and receive a priming antagonist protocol in their sequential cycle. The aim of this intervention is to suppress FSH levels at the beginning of the cycle thus preventing estradiol secretion of the leading follicle. This may contribute to better synchronization of the remaining antral follicles cohort and allow for a better cycle outcome instead of cancellation or one-month postponement. As previous studies using GnRH antagonist pre-treatment prior to GT initiation for synchronization purposes demonstrated positive results (including different patient population) , no deleterious effects are expected.