Two approved treatments for spinal anesthesia will be compared in women undergoing cesarean section.

It is usual to perform cesarean sections using spinal anesthesia with a local anesthetic (bupivacaine) plus some opioid, such as sufentanil or morphine. Both have been shown to decrease postoperative pain, but we try to check if one brings more benefit than the other.

Inclusion Criteria:

• Patients of at least 18 years.
• Patients at least 36 weeks gestation.
• Patients scheduled for non-urgent cesarean section.
• Patients classified in the physical state of the American Society of Anesthesiologists (ASA) as grade I-II, and without important fetal pathological conditions.
• Signature of informed consent that allows them to be part of the study.

Exclusion Criteria:

• Pregnant women who reject the spinal technique.
• Patients with contraindication to spinal anesthesia.
• Patients with ASA> II classification.
• Patients with multiple pregnancy.
• Patients with three or more previous cesareans,
• Patients with BMI greater than or equal to 40 kg / m2.
• Language barrier.
• Patients with pre-eclampsia.
• Patients with a history of chronic pain.
• Patients with a history of psychiatric or drug abuse.
• Patients with allergy to any of the drugs used in the study.

The study population will be pregnant women who will undergo elective cesarean section through Subarachnoid anesthesia.