SufentanilFentanylAnalgesia, ObstetricalAnalgesics, OpioidAnalgesia, EpiduralBupivacaineAlfentanilAnesthetics, IntravenousInjections, SpinalAnestheticsAnesthesia, IntravenousAnesthesia, SpinalAnesthetics, CombinedAnesthetics, LocalLabor, ObstetricPreanesthetic MedicationPain, PostoperativeAdjuvants, AnesthesiaLabor Stage, FirstDouble-Blind MethodAnesthesia, ObstetricalAnalgesia, Patient-ControlledSubarachnoid SpaceAnalgesiaAmidesPruritusAnesthesia Recovery Period