The aim of this study is to compare predecidualization and endometrial receptivity as gene expression by using subcutaneous progesterone 25 mg/day versus intramuscular progesterone 50 mg/day in healthy women of childbearing age. Both, the two drugs and the doses administered in this clinical trial, are routine clinical practice.~A controlled ovarian stimulation will be previously performed and following routine clinical practice for 10-12 days at standard doses of subcutaneous FSH 150-225 IU/day, according to BMI and number of antral follicles. A GnRH antagonist shall be administered, being initiated according to donor's follicular growth from greater or equal14 mm diameter follicles. Final maturation shall be performed with a bolus of GnRH agonist when there exist at least 3 follicles greater or equal17 mm diameter, and therefore performing follicular puncture 36 hours after the bolus of agonist has been administered.~If the donor meets the inclusion criteria, she will be informed of the study and, if she agrees, she will sign the informed consent. Randomization shall be performed in 2 arms; arm 1 will be administered subcutaneous progesterone 25 mg/day (Prolutex; Angelini, Spain), and arm 2, intramuscular progesterone 50 mg/day (Prontogest IBSA, Italy). In each arm 12 donors (ITT population) will be included.~The randomization to a treatment group shall be performed the day the follicular puncture has been programmed. To that purpose, a randomized consecutive sampling will be used by means of assignment tables. The medication will be administered by a person not involved in the assessments and responsible for group assignment, data centralization and drug assignment.~At day 5 (5 days after follicular puncture):endometrial thickness measurement by means of transvaginal ultrasound and perform endometrial biopsy and take two samples: 1 sample to Anatomical Pathology and 1 sample to Endometrial Receptivity Array (ERA).
Study the endometrial predecidualization by using subcutaneous progesterone 25 mg/day versus intramuscular progesterone 50 mg/day, to determine whether there are differences in the endometrial transformation and endometrial receptivity.