Spinal anesthesia will be performed in all cases in sitting position at L3-L4 or L4-L5 spaces with hyperbaric bupivacaine 0.5% (12.5 mg) and fentanyl 20 µg. After the umbilical cord is clamped, a 10 IU infusion of oxytocin in 500 mL of lactated Ringer's solution will be infused.