 Several factors influence the extension of anesthetic mixture during spinal anesthesia including anesthetic gravity, body position, drug volume, and drug-delivering velocity. However, the effect of temperature of anesthetic mixture on the cephalad sensory blockade is hitherto unknown. The investigators hypothesized that different temperatures of the anesthetic mixture had different velocity of extension after spinal anesthesia. In addition, previous studies suggest that parturients have relative higher sensitivity to temperature. Herein the investigators proposed that the temperature of anesthetic mixture had more extensive effect on the cephalad sensory blockade with spinal anesthesia for cesarean delivery. 