Current cesarean section often chooses spinal anesthesia. And in order to avoid the impact of drugs on the fetus, before the delivery, anesthesiologist generally don't use sedative or analgesic drugs. However, the majority of puerperas would appear nervous, anxiety, fear and other psychological reactions in cesarean section. Although the placental transfer and the foetal metabolism of dexmedetomidine have been reported and the result show no adverse effects on neonates, but the placental transfer of dexmedetomidine in intravertebral anesthesia area was lack of systematical research. This study intends to use of dexmedetomidine in the cesarean section under epidural anesthesia and investigate its effects on the parturients' haemodynamics and the neonates' placental transfer and metabolism.