Both hydromorphone and morphine are administered as part of spinal anesthesia to help improve pain control after cesarean delivery. In this study, the investigators are going to determine the doses of each of those medicines that provides optimal pain control to women undergoing cesarean delivery while limiting side effects related to those medicines. The investigators hypothesize that the doses of hydromorphone and morphine that provide optimal pain control without significant side effects will be 100 micrograms and 150 micrograms, respectively. The investigators further hypothesize that at each respective optimal dose, side effects will be less in the hydromorphone group.