The purpose of this study is to determine whether Medroxyprogesterone Acetate (MPA) administration in follicular phase prevents premature luteinization with equal efficiency as GnRH antagonists and otains similar clinical results in oocyte donation.

Within the new guidelines for stimulation, the use of oral progesterone in follicular phase allows GnRH analogue administration, resulting in greater comfort for patients as well as a reduction in cost. Obtained results are similar to those from conventional protocols in terms of: early luteinization, number of oocytes, embryos number and rate of implantation and gestation or appearance of congenital malformations. Another advantage is the lower incidence of OHSS (Ovarian Hyperstimulation Syndrome).

From a scientific point of view, it would allow a better understanding of folliculogenesis, of progesterone mechanism of action on blocking LH secretion and its effect on ovarian and later embryonic level.

From a clinical point of view, it would simplify COS (Controlled Ovarian Stimulation) by reducing the number of medication administered subcutaneously and their possible side effects on both systemic and local levels. It would be of special interest in 2 groups of patients, for example, oocyte donors and patients undergoing preservation of fertility. To date, there is a lack of studies along these lines.

Inclusion Criteria:

• Age between 18-35 years (both included)

• Regular Menses (between 25-35 days)

• Absence of physical and psychic pathologies at the time of oocyte donation

• BMI: 18-28 kg(m2 at the time of oocyte donation.

• Other criteria to comply with:

  i. With no relevant personal or family medical history ii. Signing of Informed Consent iii. From a medical point of view:

  1. Healthy ovaries and uterus, with no organic pathology

  2. Ovaries without polycystic aspect

  3. Antral Follicle Count > 12 in the sum of both ovaries

  4. Normal Karyotype

  5. Negative results in infectious illness screening (Hepatitis B Virus; Hepatitis C Virus, VIH Virus Syphilis)

  6. Results within range of general analysis of hemogram, hemostasia y biochemistry.

     Exclusion Criteria:

• Any systemic or metabolic disorder which contraindicate the use of Gonadotrophines

• Medical background of Trombophlebitis or thromboembolic phenomena or Arterial Hypertension

• Severe hepatic insufficiency, cardiovascular illness

• Suspicion or evidence of malignity of mamarian glands or other hormone dependant genital organs

• Known infection of Hepatitis B Virus; Hepatitis C Virus or VIH Virus

• Known hypersensitivity to PMA or its excipients

• Any reason or cause which excluede from the oocyte donation program

• Participation in another clinical trial in the two months prior to the inclusion on this study