A Randomized Controlled Study of Prolonging the Time of Progesterone Supplementation to Improve the Pregnancy Outcome of Single Day 6 Blastocyst Transfer of Freeze-thaw Cycle

Inclusion Criteria: 1. Aged 20 to 38 years. 2. Less than three transfers. 3. Undergoing HRT freeze-thaw cycle single blastocyst transfer in the current cycle. 4. Having consented to participate in this study and signed the informed consent form. Exclusion Criteria: 1. Chromosomal abnormality in either the patient or their partner 2. Contraindications to hormone replacement therapy. 3. Patients with intramural myoma affecting the morphology of the uterine cavity, severe adenomyosis, endometriosis, congenital uterine anomalies, endometrial tuberculosis, intrauterine adhesion and other diseases significantly affecting embryonic implantation. 4. Currently participating in another clinical study.