Effect of endometrial scratch on repeat implantation failure following in vitro fertilization embryo transfer or frozen embryo transfer

INTERVENTION: Endometrium scratching in seventh day after observation of Luteinizing hormone (LH) surge prior to an IVF or frozen embryo transfer (FET) cycle in study group. No extra administration prior to an IVF or FET cycle in control group. Control group: patients with RIF without endometrial scratch before IVF‐ET or FET. Study group: patients with RIF undergoing endometrial scratch before IVF‐ET or FET. CONDITION: Infertility ; Urological and Genital Diseases ; Female infertility PRIMARY OUTCOME: 1. Implantation rate ; 2. Clinical pregnancy rate defined as the presence of a fetal sac by ultrasound scanning SECONDARY OUTCOME: 1. Endometrial thickness ; 2. Endometrial type INCLUSION CRITERIA: 1. Patients with repeated implantation failure (two or more) undergoing in vitro fertilization embryo transfer (IVF‐ET) or frozen embryo transfer (FET) 2. Patients aged no more than 40 years old 3. Patients with basal follicle‐stimulating hormone (FSH)<10IU/L 4. Patients without history of uterine cavity operation in two months