In a prospective randomised study involving primiparous women in spontaneous uncomplicated labour with cervical dilatation < 5 cm, epidural analgesia will be given with an initial volume of 20 mL anaesthetic solution, followed by a standardised algorithm of top-up manual injections to achieve analgesia, then by a patient-controlled regimen with 5-mL self-administered boli in addition to a continuous infusion of 5 mL.hr-1. The anaesthetic solution will be levobupivacaine presented in 100-mL bags from the market (0.0625%), in which 10 mL (50 g) of sufentanil will be added, as well as clonidine (150 µg) in one arm. The final concentration of clonidine in this arm will be 1.35 mg.mL-1. Parturients and midwifes assessing pain during labour will be blinded to the design.