Study	Reason for exclusion
Anonymous 1995	Brief conference abstract. No results for groups reported (P values provided but no other data). We attempted to follow up this reference through the conference organisers but were unable to contact the author
Canino 1987	This study examined the use of TENS after Caesarean section rather than in labour
Chia 1990	20 women were included in this randomised cross-over trial; TENS to the back was compared with Entonox®. This comparison is not relevant for this review. (This study was originally included in the review but this updated version is one in a series of Cochrane reviews examining pain management in labour which contribute to an overview of systematic reviews of pain management for women in labour (Jones 2011b) and which share a generic protocol (Jones 2011a). In order to comply with the generic protocol which has specific inclusion criteria relating to comparison interventions, this trial has been moved to a review examining inhaled analgesia as it no longer meets the inclusion criteria for the TENS review
Dunn 1989	Study examining acupuncture-point TENS for the induction of labour rather than for pain relief in labour. Main outcome was the strength of uterine contractions
Erkkola 1980	Not random allocation. Women were assigned to groups alphabetically
Hulkko 1979	This study carried out in 1977 included women with post-dates pregnancies admitted to hospital for induction. Allocation to groups was not randomised
Merry 1983	This study involving 17 women used non-random methods of allocation (hospital number). The study was reported in a brief abstract
Tajali-Awal 1995	Not clear that this is a RCT. Randomisation described as sequential. There were high levels of attrition - 30% were excluded (for reasons that may have been related to outcomes of the review, e.g. if they used any other form of pain relief or had a caesarean section)
Tawfik 1982	This study was originally included in this review. This review is one in a series of Cochrane reviews examining pain management in labour. These reviews contribute to an overview of systematic reviews of pain management for women in labour (Jones 2011b) and share a generic protocol (Jones 2011a). In order to comply with the generic protocol which has specific inclusion criteria relating to comparison interventions, the Tawfik 1982 trial (TENS versus pethidine) has been moved to the Parenteral opioids review (Ullman 2010), as it no longer meets the inclusion criteria for this updated TENS review