Infant neurobehavior alteration is predictor of later intelligence development. Many factors would influence or are associated with infant neurobehavior, of which exist or appear during perinatal period. Neuraxial, especially epidural, analgesia to date is the most effective method in relieving labor pain. Although previous studies showed that opioid used in epidural analgesia for labor pain can affect newborn neurobehavior negatively in a dose-escalation associated manner, whether epidural analgesia itself would produce unpredictable effect on newborn neurobehavior is still unknown. Hereby the investigators designed this trial to investigate the hypothesis that epidural analgesia for labor pain control itself would not produce negative effect on infant neurobehavior.

Inclusion Criteria:

• >18years and <45years
• Spontaneous labor
• Analgesia request

Exclusion Criteria:

• Allergy to opioids, a history of the use of centrally-acting drugs of any sort, chronic pain and psychiatric diseases records
• Participants younger than 18 years or older than 45 years
• Those who were not willing to or could not finish the whole study at any time
• Using or used in the past 14 days of the monoamine oxidase inhibitors
• Alcohol addictive or narcotic dependent patients were excluded for their influence on the analgesic efficacy of the epidural analgesics
• Subjects with a nonvertex presentation or scheduled induction of labor