Oocyte donation is a well established procedure in assisted reproduction treatments (ART). It is demonstrated that the use of hormonal substitution therapy, for the synchronization of the cycles between the recipients and the donors, provides good results, similar to the ones obtained with the natural cycle. In the patients - recipients with preserved ovarian function, the recipient's natural cycle is annulled, thus preventing the spontaneous Luteinizing Hormone surge. Simultaneously and while waiting for the suitable donor, her endometrium is prepared. When the donation occurs and fertilization with the husband sperm takes place, her cycle is stimulated again in order to synchronize her window of implantation with the donor's ovulation. Two different medications are commonly used to inhibit spontaneous ovulation: either GnRHa agonist or GnRH antagonists. The present study consists of the comparison between the single dose GnRH agonist (Decapeptyl 3,75 IM) and the 7 day dosage of GnRH antagonist (Cetrotide 0,25 mg). The administration of GnRHa is used fundamentally as a long liberation formulation, administered in a single intramuscular injection (IM), which is more practical in terms of use. Nevertheless, the unnecessary persistence and the potentially unfavorable action of GnRHa during the luteal phase and early gestation have questioned its use. The recovery of the Hypophysarian function begins only 8 weeks after the single injection of long liberation of triptorelina 3.75 mg. The GnRH antagonist (Cetrotide 0,25 mg) makes the hypofisary inhibition shorter than with the analogues and can prepare similar endometrium characteristics as a natural cycle. The recipients will be assigned randomly to a group of treatment or another.