To evaluate if the administration of corifollitropin alfa on day 7 instead of on day 5 after pre-treatment with oral contraceptive pill results in a reduced total rFSH (recombinant follicle stimulating hormone ) consumption in a GnRH antagonist protocol in donors.

Inclusion Criteria:

• Women 18-35 y old ,with regular spontaneous menstrual cycles of 25-30 days length
• Who had vaginal sexual intercourse or have no inconvenient for vaginal explorations
• Donors can´t have more than 6 children (neither own or after donations)
• Not be adopted or being born after a gamete donation pregnancy
• BMI between 18-28 kg/m2
• Height > 1.55cm
• Gynecological and general examination with Pap smear, HIV, HCV (hepatitis C virus ), HBV (hepatitis B virus ) and RPR(rapid plasma reagin test ) negative serology, and with normal karyotype
• No abnormal Psychological profile
• Discard any disease: blood disorders, neurodegenerative/psychiatric diseases, Fragile X Syndrome, cystic fibrosis carrier, oncology diseases.
• Without psychological/psychiatric family history
• Will conform to the protocol for the duration of the study
• Willingness of adhesion to protocol during the whole study period
• Signed informed consent

Exclusion Criteria:

• Polycystic ovarian syndrome
• Antral follicle count > 20
• Hypersensitivity to the active substance or any of the excipients
• Abnormal vaginal bleeding of unknown ethiology
• Presence of ovarian cysts or increased size ovaries
• History of ovarian hyperstimulation syndrome
• Previous controlled ovarian stimulation cycle with more than 30 follicles ≥ 11mm
• Previous abdominal surgery that contraindicated the practice of follicular puncture
• HIV, HCV, HBV positive serology in women or partner
• Important systemic diseases that could interfere with gonadotrophin treatment (ovarian and hypothalamic tumors…)