 A controlled ovarian stimulation will be previously performed and following routine clinical practice for 10-12 days at standard doses of subcutaneous FSH 150-225 IUday, according to BMI and number of antral follicles. A GnRH antagonist shall be administered, being initiated according to donors follicular growth from greater or equal14 mm diameter follicles. Final maturation shall be performed with a bolus of GnRH agonist when there exist at least 3 follicles greater or equal17 mm diameter, and therefore performing follicular puncture 36 hours after the bolus of agonist has been administered. 