Healthy paturients undergoing cesarean delivery with intrathecal morphine 250g and fentanyl 25g were randomized to receive : prophylaxis ( ondansetron 8mg at cord clamping , normal saline 4mL for treatment of pruritus in the post-anaesthesia care unit ) ; treatment ( normal saline 4mL at cord clamping , ondansetron 8mg as required in the post-anesthesia care unit ) or control ( normal saline 4mL in both ) .