Women with PCE represent a treatment-resistant phenotype in whom the endometrial inflammatory and immune status remains abnormal despite antibiotic therapy. GnRH agonist pretreatment may be most beneficial in endometrial phenotypes marked by persistent or residual inflammatory impairment rather than in all frozen embryo transfer populations.We therefore conducted a single-center prospective cohort study to investigate whether GnRH-HRT, compared with non-GnRH-based preparations, improve clinical pregnancy and live birth in women with PCE undergoing FET,

Inclusion Criteria:

• Aged 20-40 years; confirmed persistent chronic endometritis (PCE) via hysteroscopy plus CD138 immunohistochemistry, defined as positive endometrial pathology after two-course antibiotic treatment for CE.
• Frozen-thawed embryo transfer (FET) with available transferable cleavage-stage or blastocyst embryos from IVF/ICSI cycles.
• No acute pelvic infection at enrollment; ≥1 month elapsed after completion of last antibiotic therapy for endometritis.
• Normal uterine cavity except for inflammatory changes of PCE; no severe uterine malformation or severe intrauterine adhesion requiring surgical intervention.
• Voluntarily sign informed consent and complete full follow-up of pregnancy outcomes

Exclusion Criteria:

• History of pelvic tuberculosis, intrauterine adhesions, submucous uterine myoma or endometrial polyp before FET
• Uncontrolled systemic endocrine disorders, autoimmune diseases (APS, SLE), severe hepatic/renal/cardiopulmonary dysfunction.
• Known allergy to GnRH agonist for down-regulation regimen; prior long-acting GnRH-a intolerance.
• Recent use of immunosuppressant, long-term glucocorticoid or drugs interfering endometrial development within 3 months before enrollment.
• Lost to follow-up or plan to abandon embryo transfer after enrollment.

This prospective cohort study enrolls infertile patients diagnosed with persistent chronic endometritis who receive FET in reproductive center. Subjects are allocated into two groups: down-regulation endometrial preparation group and conventional artificial cycle or natural cycle group. We compare implantation, clinical pregnancy, miscarriage and live birth rates between two regimens.