Impact of the Presence of the Corpus Luteum on Pregnancies Obtained Through Frozen Embryo Transfer(FET)

Inclusion Criteria: * Female patients 18- 37 years old (both included) at the time of oocyte retrieval and less than 41 years of age at the time of embryo transfer. * Regular menstrual cycles between 24 and 35 days. * Availability of cryopreserved blastocysts from own gametes * Indication for single embryo transfer. * Patients who will be included in the LUTI study are candidates for either of the two procedures under study, and will have no contraindications for either procedure. Exclusion Criteria: * Recurrent pregnancy loss (3 or more). * Recurrent implantation failure in previous IVF treatments (3 or more unsuccessful embryo transfers). . * Diagnosis of polycystic ovarian syndrome, diabetes mellitus, chronic arterial hypertension, maternal heart disease and autoimmune diseases (Systemic Lupus Erythematosus (SLE) or Antiphospholipid syndrome (APS)). * Active treatment with aspirin, heparin or other anticoagulant therapy, antihypertensives or other drugs used to treat circulation or coagulation disorders . * Indication for PGT (Preimplantation Genetic Testing). * Multiple pregnancy.