Vaginal Progesterone Improves Clinical Outcomes of RIF Patients

Inclusion Criteria: 1. Aged between 20 and 40 years old; 2. BMI: 18-28 kg/m2； 3. Consistent with the diagnosis of repeated implantation failure of unknown reasons, the previous embryo transfer situation meets one of the following: Total embryos transferred ≥ 4 high-quality cleavage-stage embryos; ≥ 2 blastocysts; ≥ 2 high quality cleavage-stage embryos +≥ 1 blastocysts; 4. At least 1 high-quality embryo remained for embryo transfer; 5. Volunteer to participate in the study and sign the informed consent form. Exclusion Criteria: 1. Patients with recurrent pregnancy loss (≥ 2 biochemical pregnancies or ≥ 2 spontaneous abortions); 2. Adverse pregnancy history (stillbirth, fetal malformation, etc.); 3. Severe paternal factors: need for TESA or PESA; 4. PGT; 5. Failure of embryo implantation due to any definite reason, including but not limited to: endometrial adhesion (moderate to severe), thin endometrium (\<7 mm before transformation), endometritis, endometriosis (medium or severe), adenomyosis, untreated hydrosalpinx, hysteromyoma (submucosal fibroids, non submucosal fibroids \> 4.0 cm and/or endometrial compression), reproductive malformation, serious immune disease, serious coagulation function abnormality; 6. Chromosome abnormality of either spouse; 7. Those with contraindications to pregnancy or assisted reproductive technology.