The primary purpose of this study is to evaluate the effect of the two different protocols (long protocol vs antagonist protocol) on oocyte / embryo quality.

The cycles with antagonists of the GnRHa present a series of advantages with respect the GnRHa in an oocyte donation program: treatment cycles are simpler and shorter, a lower amount of dose of gonadotrophins is needed for stimulation, and most important, a decreased rate of ovarian hyperstimulation syndrome is observed. Nevertheless, several clinical trials relate their use to a greater rate of abortion and worse oocyte/ embryo quality. In order to discriminate the endometrial factor from the quality of oocyte cohort, the best strategy is the oocyte donation model. In the present study, for the first time, the effect of different protocols (long versus antagonist protocol) will be studied in the same donor, acting as its own control, undergoing COH. We will compare the COH´s parameters and IVF outcome obtained in the same donor submitted to, firstly, GnRH antagonist protocol (Cetrorelix- n= 45) versus another consecutive cycle with long protocol (Ac. Leuprolide- n= 45).

Inclusion Criteria:

• oocyte donors with age range: 18 - 34; BMI: 18 - 29 kg/m2;

Exclusion Criteria:

• PCO