The incidence of postpartum depression in Europe and the United States is about 10%, while in China the incidence rate of 15.7-39.8%. Postpartum depression is one of the most common diseases of perinatal distress, but the current research of high-quality prevention and treatment of postpartum depression is still very lack. The study suggests that the risk of postpartum depression in cesarean delivery is significantly higher than that in vaginal delivery. Therefore, postpartum depression in cesarean delivery may require more attention and treatment.Tramadol is a non-opioid central analgesic that relieves common to severe pain, and tramadol has an inhibitory effect on norepinephrine and serotonin systems and has the potential to reduce depression and anxiety. Therefore, for the analgesic demand and antidepressant demand for maternal who undergoing cesarean section, tramadol may be an optimized and effective analgesic for the prevention and treatment of postpartum depression.

This study was designed according to a prospective, randomized, controlled clinical trial. Randomized subjects were randomly assigned to different analgesic drug-treated groups according to the random number induced by SPSS software. All three analgesic treatments were routinely used for clinical analgesia; Anesthesia, surgery, postoperative treatment are in accordance with clinical practice. The investigators conducted a postoperative questionnaire survey and psychological diagnosis for all patients. And blood sample was collected from patients before and 48 hours after the surgery.

Inclusion Criteria:

• 20 years old ≤ age ≤ 40 years old;
• ASA score I-Ⅱ;
• uncomplicated and singleton full-term pregnancy;
• voluntarily to receive cesarean section and postoperative controlled analgesia;
• consent to participate the study.

Exclusion Criteria:

• with history of mental disorders or psychotropic substances use;
• with history of neurological diseases such as epilepsy
• with history of previously known diagnosed depression;
• with suicidal ideation or history of suicide;
• with history of drug，alcohol or opioid abuse;
• with monoamine oxidase (MAO) inhibitor treatment at present or in the past 14 days;
• participating in other clinical studies
• with severe heart disease, brain disease, liver disease and kidney disease;
• be allergic to tramadol or opioids;
• with any contraindication for combined spinal epidural anesthesia;
• incapable of communication or cooperation.