The primary aim of this study is to measure the magnitude and duration of trans-abdominis plane (TAP) block analgesia in parturients undergoing elective cesarean section with concurrent standard of care operative analgesic regimens including intrathecal morphine sulfate (ITMS). A one sided block model takes advantage of the bilateral nature of the pain created by a bilateral surgical wound and allows each patient to serve as her own control. Reduced variability allows a more definitive establishment of analgesic benefit for this block.