Cesarean section scar defect (CSD) is a novel recognized cause of postmenstrual abnormal uterine bleeding in women. No clinical guidelines have been issued for the management of CSD. The investigators have previously demonstrated that vaginal repair of CSD was an relative effective treatment of CSD. However, only 28.2% of the CSD patients normalized to less than 7 days of menstruation, whereas 51.2% of women had 7 to 10 days of menstruation at 6 months post vaginal repair. The previous research suggested that the occurrence of CSD may be related to the aging phenotype of the myometrium. Metformin, as a classic diabetes treatment drug, has an important position in anti-aging therapy. Therefore, the randomized study was designed to evaluate whether the application of metformin in combination with vaginal repair could achieve better clinical effects than those achieved by vaginal CSD repair alone.

The previous research suggested that the occurrence of cesarean section scar defect (CSD) may be related to the aging phenotype of the myometrium. The aging of the myometrium in some cesarean section patients reduces the proliferation and repair of smooth muscle cells and endometrial cells to a certain extent. The prognosis of vaginal repair is poor and the repair of the endometrium during menstruation is not good.

Metformin, as a classic diabetes treatment drug, has an important position in anti-aging therapy. Its research and application range is the widest, and significant results have been achieved in a number of clinical trials. At the same time, its side effects are less than other anti-aging drugs, and the patient adaptability is better. It maybe the best choice for the treatment of anti-aging diseases. Therefore, the randomized study was designed to evaluate whether the application of metformin in combination with vaginal repair could achieve better clinical effects than those achieved by vaginal CSD repair alone.

Inclusion Criteria:

1. Patients are younger than 40 and over the age of 18.
2. Clearly diagnosed with CSD.
3. Experiencing clinical features of abnormal uterine bleeding, prolonged menstrual flow (the duration of menstruation is more than 10 days).
4. The thickness of the remaining muscular layer of CSD was less than 3 mm.
5. Normal range of blood sugar and insulin
6. No serious medical problems (important viscera function in the normal range).
7. No uterine fibroids, endometriosis, adenomyosis
8. No malignant tumors.
9. Sign the informed consent.

Exclusion Criteria:

1. Over the age of 40 or younger than 18;
2. Indefinite diagnosis.
3. Malignant tumors.
4. With severe medical problems (severe liver disease, kidney disease, respiratory diseases, heart disease or uncontrolled diabetes, epilepsy, etc., dysfunction of important organs).
5. Contraindications to metformin (baseline creatinine >124μmol/L, hypersensitivity to metformin, or a metabolic acidosis), use of drugs that might interact with metformin (glyburide, furosemide, or cationic drugs)
6. Pregnant.
7. Mental diseases.
8. Unwilling to comply with the research plan.