Since epidural analgesia has been developed to relieve labour pain, many solutions have emerged to lower risk / efficacy ratio, by using low-concentrated and/or less toxic local anaesthetics. Levobupicaine emerges as a safer alternative than its racemic parent . It is available on the French market in pre-filled bags with two different concentrations (0.625 and 1.25 mg.mL-1), both indicated for analgesia in postoperative context and in labour, without more precision. Presentation in bags allows preparing once at the initiation of epidural analgesia a solution usable throughout labour, leading the anaesthetist to a univocal choice, mostly following his/her personal beliefs. Our aim is to compare the effects of epidural analgesia under these two presentations. Sufentanil will be added to levobupicaine whatever the concentration used. This trial is conducted in primiparous, in which pain during labour is commonly more resistant to relief.