This study trials a new Vital signs-controlled patient-assisted intravenous analgesia (VPIA) regimen using a purpose-built pump that aims to enhance the efficacy, safety and personalization of remifentanil therapy for labouring women. The system studies the parturient's pattern of analgesic use in 15 minute epochs and titrates the demand doses and basal infusion rate to maintain a plasma level of remifentanil that is appropriate for the degree of pain felt.