Ovarian stimulation protocol will include the use of a GnRH agonist (Superfact; Aventis Pharma Deutshlan, Frankfurt, Germany) administered in the long (down-regulation) protocol and the subsequent addition of FSH (Gonal F, Sereno, Switzerland). Embryos will be initially cultured in G1.V5 medium) Vitrolife-Sweden)TM on day 1 and 2, being transferred from this medium to G2.V5 ) Vitrolife-Sweden)TM on day 3. Embryos will be transferred on day 5, depending on the degree of expansion of the blastocyst.