UMBILICAL CORD DONORS  Donors of umbilical cord blood will be women (and their partners, if applicable) who give birth to a live newborn(s) in the Gynecology and Obstetrics service of HUP La Fe; the same umbilical cord collection criteria will be followed as standardized in HUP La Fe for the donation of this biological product.  GROUP A  Inclusion Criteria:  Patient information sheet and signed informed consent. Female, acting voluntarily, aged between 18 and 48 years at the time of recruitment. BMI ≥ 18 kg/m2 and ≤ 35 kg/m2. Patients with premature ovarian failure (amenorrhea prior to 40 years of age and FSH > 40 IU/L).  Exclusion Criteria:  Active genital infection proven at the time of recruitment; chronic endometritis. Known endometrial pathology. Psychological disorder that may hinder study follow-up. Positive results after viral safety analysis (HBsAg, HBcAb, HCV, HIV1, HIV2, syphilis). Presenting any syndrome or condition that, from the principal investigator's point of view, could pose a risk to the study or to the patient. Any significant clinical anomaly detected during the recruitment process; simultaneous participation in another clinical study that could affect the objectives of the present study or previous participation in this same study.  GROUP B  Inclusion Criteria:  Information and signed informed consent. female, acting voluntarily, aged between 18 and 48 years at the time of recruitment. body mass index (BMI): ≥ 18 kg/m2 and ≤ 35 kg/m2. Patients undergoing an assisted reproduction cycle. Endometrial thickness < 5mm despite estrogen administration for more than 10 days and/or evidence of Asherman's Syndrome.  Exclusion Criteria:  Active genital infection proven at the time of recruitment; chronic endometritis. Known endometrial pathology. Psychological disorder that may hinder study follow-up. Positive results after viral safety analysis (HBsAg, HBcAb, HCV, HIV1, HIV2, syphilis). Presenting any syndrome or condition that, from the principal investigator's point of view, could pose a risk to the study or to the patient. Any significant clinical anomaly detected during the recruitment process; simultaneous participation in another clinical study that could affect the objectives of the present study or previous participation in this same study.