Inclusion Criteria:  Patients undergone ART with frozen embryo transfer, blastocyst or cleavaged stage embryo transfer, from 18-45 years of age Normal BMI HRT for Endometrial preparation in FET cycles  Exclusion Criteria:  Oocyte donor cycles Surrogacy IVM PGT Abnormal Uterine (firbroids 0 -> 3 according to FIGO classification, polyp, adenomyosis, congenital malformation) Uterus fibroids type 4,5 (Figo classification) > 4cm History of recurrent implantation failure Endometrial thickness <7mm on the day of ET Cesarean scar defect (isthmocele)