Based on randomization, patients will receive a mixture for spinal anesthesia and will be followed in the following hours for the various outcomes and for functional recovery

In the study intervention group every patient will receive a spinal anesthesia composed by hyperbaric bupivacaine 12 mg 0,5 %, morphine sulfate 100 mcg and an added randomized dose of 10 or 20 mcg IT fentanyl. The spinal anesthetic will be administered with a 27 gauge Whitacre needle at the L2-3 or L3-4 intervertebral space with the patient in sitting position. Sterile saline will be used to dilute the mixture to a final volume of 3.1 mL. The allocated treatment will be kept a secret from the patient, the anesthesiologist managing the patient, and the entire study team. The fentanyl doses will be prepared by an anesthesiologist who will not be involved in the study or the patient's treatment. For 24 hours following surgery, each patient would receive intravenous patient-controlled morphine analgesia. In the control group every patient will receive a spinal anesthesia composed by hyperbaric bupivacaine 12 mg 0,5 % and morphine sulfate 100 mcg. The spinal anesthetic will be administered with a 27- gauge Whitacre needle at the L2-3 or L3-4 intervertebral space with the patient in sitting position. Sterile saline will be used to dilute the mixture to a final volume of 3.1 mL. The allocated treatment will be kept a secret from the patient, the anesthesiologist managing the patient, and the entire study team. For 24 hours following surgery, each patient would receive intravenous patient- controlled morphine analgesia.

Inclusion Criteria:

• patients over 18 year of age
• height over 160 cm
• American Society Anesthesiologists physical status I and II
• term singleton parturients
• scheduled for elective cesarean delivery during spinal anesthesia at Ospedale Regionale Bellinzona Valli

Exclusion Criteria:

• patients with inability to consent
• patient refusal
• contraindication to spinal anesthesia (eg, hemodynamic instability, infection at the surgery site, and neurologic defects such as transverse myelitis)
• emergency cesarean delivery
• preeclampsia/eclampsia
• allergy to drugs used in the protocol

the study involves pregnant patients

Allocation will take place immediately before the intervention by the means of access to centralized, real-time allocation through a computer program. The identification code will be present on the data collection form (where the patient's name, surname or date of birth will not appear to ensure blinding of the study).

Personnel not directly involved with patient care, present during the randomization process, will sterilely prepare anesthesia solution while maintaining a total volume of 3,1 ml. This will allow blinding of patients, care providers and data collectors. The procedure will take place as a common clinical practice in our center. When performing spinal anesthesia, sterility is of fundamental importance, so it will not be possible to have the syringe used tagged. In the kit all materials will be sterile