Retained product of conception (RPOC) is defined by abnormal trophoblastic persistence or retained placenta inside the uterus cavity after a pregnancy independently of the outcome. Untreated RPOC can compromise future fertility. RPOC are generally treated surgically, either by repeated evacuation or by hysteroscopy, which exposes the uterus to additional potential trauma.The combination of trauma to the gravid uterine cavity, hypoestrogenic state at the time of the operation or immediately afterward and local infection is considered to be the pathogenic mechanism of intrauterine adhesions (IUA) , manifested clinically by menstrual abnormalities, infertility and recurrent pregnancy loss.To investigate the efficacy of auto-cross linked hyaluronic acid gel in the prevention of adhesion reformation after hysteroscopic resection of retained products of conception. After the completion of hysteroscopic resection of retained products of conception, patients will be randomized to one of the two groups by computer-generated numbers: \[1\] infusing auto-cross linked hyaluronic acid gel into intrauterine cavity in the experimental group; \[2\] no auto-cross linked hyaluronic acid gel into intrauterine cavity in the control group. Second and third look outpatient hysteroscopy will be performed 4 and 8 weeks after the initial surgery. The patients will be followed up about menstrual pattern at 3 months after the surgery.The patients will be followed up about pregancy outcome at 12 months after the surgery.