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.