Randomised, prospective, investigator-blinded, controlled, single-centre study to assess the impact on the ongoing pregnancy rate with the use of two progesterones with different administration routes, in recipients of fresh embryos from donor oocytes, undergoing endometrial preparation for fresh embryo transfer.

Exploratory study with a control group treated according to our Service's usual therapeutic regimen for the transfer of embryos with donor oocytes.

The controlled ovarian stimulation protocol in oocyte donors is always calculated according to the standard protocol at the Bernabeu Institute. Endometrial preparation will be carried out following the standard protocol of the Bernabeu Institute as follows: the oestrogen will be administered transdermally and patients with maintained ovarian function undergo medical hypophysectomy with depot GnRH agonists administered in the mid-luteal phase of the previous cycle.

On the day of oocyte retrieval, the patient will be randomised: Group A will be administered subcutaneous progesterone 25 mg/day (Prolutex), and Group B will be administered vaginal progesterone in capsules 200 mg/3 times a day (Progeffik).

The embryo transfer will be performed on day 5 of the embryo culture (Day +5). A biochemical pregnancy test beta- hCG and the P4 analysis will be performed 14 days after oocyte retrieval.

All the cycles will be monitored according to the Department's standard criteria, using transvaginal ultrasound to assess embryonic development and endometrial thickness, as well as analytical controls.

The study will be blinded to the investigator. The evaluating professionals will not know if the subject has been administered vaginal progesterone or subcutaneous progesterone. The medication will be delivered by a person who does not participate in the evaluations and who is dedicated to group assignment, to data centralisation, and to delivering the medication.

The aim of this study is to determine if the ongoing pregnancy rate in patients undergoing a fresh embryo transfer cycle with donor oocytes is affected by the progesterone administration route.

Inclusion Criteria:

• Female, aged from 18 to 49 years (both inclusive)
• Woman who wishes to become pregnant
• Endometrial thickness greater 7 mm on the day of patient randomisation to one of the progesterone groups
• Six or more donor retrieved oocytes
• Patient programmed for fresh embryo transfer on day +5 of embryo culture
• BMI lower than 30 Kg/m2
• Infertility that justifies treatment with donor oocytes
• Male with no known karyotype alterations
• Semen by ejaculation from either the partner or from a bank
• Uterus able to support embryo implantation and pregnancy
• Absence of pregnancy before starting the embryo transfer cycle
• Has given prior written consent

Exclusion Criteria:

• - Important systemic diseases, endocrine-metabolic abnormalities involving the pituitary, thyroid, adrenals, pancreas, liver or kidney.
• HIV, HBV or HCV seropositivity
• Undiagnosed vaginal bleeding
• Pregnancy, breastfeeding or any contraindication to becoming pregnant
• Malformation of sexual organs incompatible with pregnancy
• Known allergy to progesterone preparations or their excipients
• Current dependence on alcohol, drugs or psychotropic medication
• Concurrent participation in another study
• Concomitant medication that could interfere with the study medication: different hormonal treatments used in the study, except thyroid hormones, antipsychotics, anxiolytics, hypnotics, sedatives, chronic treatment with prostaglandin inhibitors