Secondary objectives To chart a derived dose response curve for bupivacaine, levobupivacaine and ropivacaine after intrathecal and extradural injection Determine the intrathecal / epidural potency ratio of each drug To measure the degree of motor block using Bromage and Straight Leg Raising scales To measure side effects such as hypotension, nausea and vomiting To measure mode of delivery and fetal outcome