 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. 