SufentanilAnalgesia, ObstetricalInjections, SpinalAnalgesics, OpioidAnalgesia, EpiduralLabor, ObstetricPain MeasurementDouble-Blind MethodFentanylPregnancyBupivacaineAnesthesia, SpinalAlfentanilAnesthetics, LocalMorphineAnesthetics, IntravenousAnestheticsInfusion Pumps, ImplantablePain, PostoperativeAdjuvants, AnesthesiaAnesthesia, IntravenousAnesthesia, ObstetricalSubarachnoid SpaceAnalgesiaAnalgesicsAnesthetics, CombinedSpinal CordPreanesthetic MedicationPruritusClonidine