Intrauterine adhesions (IUA) is a group of diseases caused by endometrial injury leading to occlusion of the uterine cavity and serious abnormality of the uterine cavity morphology, which causes primary or secondary infertility by affecting embryo implantation. At present, the poor effectiveness of clinical treatment methods has made the thin endometrium after intrauterine adhesions an urgent problem to be solved in the clinical field of assisted reproduction.

Stem cells with multi-directional differentiation potential provide a new idea for the treatment of cervical adhesions. However, due to limitations such as stem cell extraction, technical conditions, and ethical issues, clinical application cannot be widely carried out. Exosomes are vesicle structures produced by paracrine secretion of cells, containing abundant proteins, RNA, etc., and mediating information exchange between cells. Recent studies have found that stem cells play a role in tissue repair mainly through paracrine, and stem cell-derived exosomes have similar functions to stem cells. Human cord mesenchymal stem cells were selected as an intervention for this clinical study because of their wide source, easy access, and low immunogenicity.

Therefore, in this clinical study, the investigator will evaluate the clinical safety and efficacy of infusing human umbilical cord mesenchymal stem cell exosomes into the uterine cavity for the treatment of thin endometrium after intrauterine adhesions.

Inclusion Criteria:

• (1) The subjects were able to fully understand the purpose of the screening and the trial, had sufficient understanding and compliance with the research protocol, and signed the informed consent form; (2) The subjects were aged between 20 and 38 years old; (3) The body mass index was 18-27 kg/m2; (4) The menstrual cycle was regular for at least half a year, with a duration of 27-35 days; (5) The ovarian reserve was normal, with at least 6 follicles (AFC), and the serum follicle-stimulating hormone (FSH) level on the 2nd-4th day of the menstrual cycle was between 1-10 IU/L, and other basic hormone indicators were within the normal range of clinical laboratories; (6) The serum human immunodeficiency virus (HIV) antibody, Treponema pallidum particle agglutination test (TPPA), hepatitis B surface antigen (HBsAg), and hepatitis C virus antibody (HCV-Ag) tests were negative within half a year; (7) Previous hysteroscopy diagnosis was moderate to severe intrauterine adhesions (AFS > 5 points); (8) There was a history of canceling frozen embryo transfer due to repeated B-ultrasound monitoring of thin endometrium and poor endometrial response (HRT cycle or/and late proliferative endometrium thickness < 6mm).

Exclusion Criteria:

• (1) Those who cannot accept the treatment and observation process as required by the trial; (2) Those with contraindications for hysteroscopic surgery; (3) Congenital uterine malformations; (4) Severe adenomyosis; (5) Uterine fibroids that may affect embryo implantation; (6) Other uterine factors judged by the researchers to be unsuitable for embryo implantation; (7) Patients with chromosomal abnormalities; (8) Patients with reproductive system tuberculosis, or those with immune system diseases (such as rheumatoid arthritis, systemic lupus erythematosus, etc.); (9) Chronic wasting or bleeding disorders; (10) Unaddressed tubal hydrosalpinx; (11) Contraindications for estrogen therapy; (12) Patients with systemic diseases， such as thrombosis， heart and lung diseases， hematological system diseases and malignant tumors， etc.