BACKGROUND: One previous study has confirmed that the marginally hyperbaric solutions of bupivacaine can maintain good quality of anesthesia and get a more steadily hemodynamic status than commonly hyperbaric solutions, some authors confirmed the plain ropivacaine for cesarean section have a higher failure rate and commonly hyperbaric solutions of ropivacaine have a higher incidence of side reaction. It is unclear what the efficacy of spinal marginally hyperbaric ropivacaine for elective cesarean delivery.We hypothesized that the marginally hyperbaric ropivacaine will get a similar efficacy to commonly hyperbaric solutions but a more steadily hemodynamic status.