Elevation of uterine basal tone after combined spinal epidural or epidural labor analgesia and its association with fetal heart rate abnormalities: a randomized double-blind study

INTERVENTION: combined spinal epidural analgesia with initial intrahecal injection of bupivacaine 2,5 mg with 2,5 mcg sufentanil epidural analgesia with initial epidural injection of 12,5 mg bupivacaine with 10 mcg sufentanil CONDITION: fetal heart rate abnormalities and elevation of the uterine basal tone occurring after labor analgesia PRIMARY OUTCOME: Occurrence of elevation of uterine basal tone associated with nonreassuring fetal rate tracings after labor analgesia INCLUSION CRITERIA: laboring patients in active phase of labor with cervical dilatation between 3 and 7 cm, who asked for labor analgesia