Linear regression analysis between patient’s age and number of oocytes in the GnRH agonist group (A) and the GnRH antagonist group (B). In GnRH antagonist protocol it was observed a positive correlation between number of oocytes and patient’s age: the luteo-follicular transition induces FSH levels above the treshold for a short-period until hormonal feedback occurs, leading to the initiation of follicular growth of a few leading follicle. After exogenous FSH administration, FSH levels arise above threshold again and will initiate several additional follicles to grow, leading to a less synchronization of the follicular cohort, and a more natural recruitment of follicles. In GnRH antagonist protocol no correlation was observed between number of follicles and patient’s age. In GnRH agonist protocol, FSH levels remain above the threshold following pituitary downregulation and FSH exogenous administration, resulting in a more synchronized follicular recruitment (Depalo et al., Gynecol Endocrinol. 2009).