Prolonged Progesterone to Prevent Preterm Birth From IVF - ET

Inclusion Criteria: 1. 20-40 years old 2. met the conditions of assisted reproductive technology and underwent IVF fresh embryo transplantation 3. Singleton pregnancy 4. Patients volunteered and signed informed consent prior to the trial. Exclusion Criteria: 1. >40 years old 2. History of miscarriage or cervical insufficiency in the second trimester 3. Abnormal ovarian function or surgical history: decline in ovarian reserve, premature ovarian failure, Turner's syndrome, ovarian cyst excision, PCOS perforation/coning, chocolate cyst surgery, ovarian cone resection 4. Uterine deformities: including single horn uterus, double horn uterus, residual horn uterus, saddle uterus, infantile uterus, double uterus, mediastinal uterus 5. Diseases affecting uterine shape: uterine adhesions, uterine submucosal myomas or polyps, adenomyosis, chronic inflammation of the endometrium 6. Abnormalities in cervical morphology or function. 7. History of total cervicectomy, conical excision, and cervical insufficiency 8. Vaginal inflammation: refractory candida vaginitis, bacterial vaginosis, persistent mycoplasma-positive vaginosis, persistent chlamydia-positive vaginosis 9. B ultrasonography indicates twin or multiple pregnancies 10. Patients with severe medical and surgical diseases 11. Participants who had participated in other clinical trials during the 90 days or had received any investigational clinical drug during the 30 days prior to the trial 12. Patients with no long-term follow-up or poor compliance 13. The investigator believes that there are any factors that may affect participants' participation in the study or the evaluation of the results