A Randomized Controlled Study of Uterine Incision Diverticulum Repair vs. no Repair During Second/Third Cesarean Section

The goal of this study is to assess the efficacy and safety of uterine incision diverticulum repair during repeat cesarean section.The main questions it aims to answer are: * Can this surgical method improve the symptom of menorrhagia？ * Is this procedure safe？ Researchers will compare experimental group(Cesarean section + diverticulum repair group) to control group(Conventional cesarean section group) to see if this surgical method works to treat or improve menorrhagia. Participants will: * randomly assigned 1:1 to the experimental group（repairing uterine diverticula during cesarean section) and the control group （Routine cesarean section without repairing the uterine incision diverticulum） * visit the hospital 42 days after surgery * followed up by telephone 6-12 months after surgery