The goal of this clinical trial is to test a new approach: delivering human bone marrow mesenchymal stem cells (hBMSCs) via the uterine artery to treat infertility caused by severe intrauterine adhesions (IUA). This method may help stem cells better reach the deep layer of the endometrium, promote endometrial repair, and improve pregnancy chances.

Primary Objective: To assess whether stem cell therapy improves pregnancy success rates (clinical pregnancy rate after embryo transfer) in infertility patients with severe IUA undergoing IVF.

Secondary Objectives:

1. To evaluate the safety of stem cell therapy (e.g., side effects or complications).
2. To explore how stem cells help repair the endometrium (e.g., by promoting endometrial growth or improving uterine conditions).

By tracking endometrial thickness, embryo implantation rate, clinical pregnancy rate, and other indicators, we will evaluate whether this new approach is safe and effective.

Treatment Groups:

Control group: Standard hormone replacement therapy (HRT) cycle medication only.

Stem cell therapy group: Standard HRT medication + hBMSC infusion via uterine artery.

Both groups will undergo embryo transfer, and clinical pregnancy rates will be compared.

Inclusion Criteria:

1. Subjects fully comprehend the screening process and study objectives, demonstrate adequate understanding of and compliance with the trial protocol, and provide signed informed consent.
2. Age between 20 and 38 years.
3. Body mass index (BMI) 18-27 kg/m².
4. Regular menstrual cycles (27-35 days) for ≥6 months.
5. Normal ovarian reserve: Antral follicle count (AFC) ≥6; Follicle-stimulating hormone (FSH) 1-10 IU/L on cycle days 2-4; Baseline sex hormones within normal laboratory ranges.
6. Negative serology within 6 months for: HIV antibodies; Treponema pallidum antibodies (TPA); Hepatitis B surface antigen (HBsAg); Hepatitis C virus antibodies (HCV-Ab).
7. ≥2 good-quality blastocysts (D5/D6) according to Gardner grading criteria.
8. Prior hysteroscopic diagnosis of severe intrauterine adhesions (IUA) treated with electroresection, with normal uterine cavity morphology confirmed by hysteroscopy within 3 months.
9. History of canceled frozen embryo transfers due to persistently thin endometrium (<6 mm) in HRT and/or natural cycles during the late proliferation phase.

Exclusion Criteria:

1. Ovarian cysts ≥20 mm, submucosal/intramural uterine fibroids >30 mm, pituitary tumors, or malignancy in any organ.
2. Clinically significant uterine (endometrial polyps, IUA, malformations, endometriosis) or adnexal (hydrosalpinx) abnormalities.
3. Recurrent implantation failure (≥3 consecutive transfers with ≥6 good-quality embryos failing).
4. Unexplained abnormal vaginal bleeding.
5. Active pelvic inflammatory disease.
6. Reproductive tract malformations incompatible with pregnancy.
7. Abnormal cervical cytology (TCT) within 1 year before screening.
8. Severe hepatic/renal impairment, cardiac disease, or hypertension.
9. History of thrombophlebitis or thromboembolism.
10. Platelet count <100×10⁹/L, hemoglobin <100 g/L, or hematologic disorders (e.g., idiopathic thrombocytopenic purpura).
11. Clinically significant systemic diseases (e.g., diabetes, tuberculosis).
12. History of recurrent miscarriage.
13. Chromosomal abnormalities in either partner.
14. Genetic disorders (per Maternal and Infant Health Care Law) contraindicating pregnancy in either partner.
15. Exposure to teratogenic radiation, toxins, or medications in either partner.
16. Participation in other drug/device trials within 3 months prior to enrollment.
17. Any condition (comorbidity, surgery, medication, or abnormal lab results) deemed by investigators to affect trial outcomes.
18. Inability or refusal to comply with protocol requirements (including scheduled visits and tests).