Inclusion Criteria:  nulliparous, 36 - 42 gestational week, active stage of labor, less than 5 cm cervical dilatation;  Exclusion Criteria:  < 18 years; ASA > 2; refusal of informed consent; known fetal pathologies; conditions that contraindicate the execution of neuro axial analgesia techniques; uterine anomalies or previous uterine surgery; severe obesity; twin pregnancy; non-vertex fetal presentation.