A Prospective Randomized Controlled Trial, the goal of this clinical trial is to evaluate the efficacy and safety of doxycycline alone versus doxycycline plus medroxyprogesterone acetate (MPA) in women with chronic endometritis (CE), and to assess subsequent reproductive outcomes. Participants will be randomly assigned to one of two groups and will receive the assigned treatment. Participants will be followed for reproductive outcomes, including pregnancy , ongoing pregnancy, spontaneous miscarriage, and live birth.

Inclusion Criteria:

• women aged 20-45 years;
• plans to conceive within 12 months;
• chronic endometritis(CE) confirmed by endometrial CD138 immunohistochemistry (IHC);
• a diagnosis of recurrent reproductive failure(RRF);
• willingness to undergo hysteroscopy and endometrial biopsy;
• no contraindications to the study medications.

Exclusion Criteria:

• acute genital tract infection, gynecologic malignancy, endometrial hyperplasia, or uterine fibroids;
• pregnancy or lactation;
• contraindications to hysteroscopy or anesthesia;
• use of antibiotics, glucocorticoids, estrogens, or progestins within 3 months before trial initiation;
• allergy to doxycycline or medroxyprogesterone acetate(MPA);
• abnormal semen parameters in the male partner.