Efficacy of Micronized Natural Progesterone vs GnRH Antagonist in the Prevention of LH Peak During Ovarian Stimulation.

Inclusion Criteria: * Eligibility for the oocyte donation program at Instituto Bernabeu. * Age between 18 and 33 years * BMI \>18 and \<30 * Overall antral follicle count \>8 * Presence of both ovaries * Ability to participate and comply with the study protocol * Oral and written comprehension of Spanish * Having given written consent Exclusion Criteria: * Endometriosis at any stage * Any ovarian tumor whether benign or malignant * Concurrent participation in another study * Malabsorptive syndromes that may alter the efficacy of Seidigestan ® such as bariatric surgery, ulcerative colitis or Crohn's disease * Irregular periods * Hypogonadotropic hypogonadism * Having received in the previous two months treatment with ovulation stimulators * Having previously participated in the present study