Inclusion Criteria:  Aged 20 to 80. Planing to undergo caesarean section with spinal anesthesia. Scheduled to undergo cesarean section between 38 and 40 weeks of gestation. American Society of Anesthesiology Physical Class 1-2. Planing to alleviate postoperative pain with intravenous patient-controlled analgesia or administration of NALDEBAIN.  Exclusion Criteria:  Adopting rooming-in. Unable to receive opioids or NSAIDs due to contraindication. Long-term use of opioids or drug abuse. Suffering from chronic pain disease. Having medical history of mental illnesses. Diagnosed with Pre-eclampsia or eclampsia. Diagnosed with gestational diabetes. Unsuitable for participation judged by investigator.