Currently, controlled ovarian stimulation (COS) in oocyte donors is performed by daily injections of gonadotropins( recombinant FSH) plus a GnRH Antagonist usually form 5th-6th stimulation day until ovulation induction with a bolus of another injection of a gonadotropin-releasing hormone (GnRH) Agonist. Injections of the GnRH Antagonist avoid untimely luteinizing hormone (LH) surge and spontaneous ovulation prior to follicular aspiration. There is a preparation of long-acting recombinant follicle stimulating hormone (rFSH= (corifollitropin alfa (FSH-CTP), Elonva®, MSD), that allows that a single subcutaneous injection substitutes the first 7 days of daily gonadotropin injections. On the other hand, a contraceptive oral progesterone only( Desogestrel, DSG) is available for contraception, avoiding the LH surge.

In donors, by administering a single injection of FSH-CTP and oral desogestrel since the first menstruation day, the total number of injections administered is reduced and less discomfort is experienced without adverse impact on ovarian response.

Other authors have reported good results using similar synthetic progestins (Medroxyprogesterone, dihydrogesterone, and natural progesterone).

No description of the hormonal and ovarian response under this protocol has been published. Direct comparison between this novel protocol and the classical GnRH- antagonist plus daily gonadotropins has not been reported.

Inclusion Criteria:

-Fulfilling inclusión medical and legal criteria (RD - Spanish law adapting european rule-9/2014)

• Who had had undergone previously convencional COS (controlled ovarian stimulation) with FSH-CTP and daily antagonist injections
• Given signed consent form.

Exclusion Criteria:

• Previous low response to COS
• Previous ovarian hyperstimulation syndrome.
• Ovarian cysts.

- Population: donors (18-35 ) from candidates of Donor program