Olsén 2007.

Study characteristics
Methods	Type of study: parallel RCT. Condition and number of participants randomised: newly delivered women with pain from postpartum uterine contractions (N = 21). Groups: HI TENS group (N = 13); LI TENS group (N = 8).
Participants	Demographics: N = 21, all female, 31 yrs (mean). HI TENS Group, 31 ± 4.2 yrs; LI TENS Group, 31 ± 4.8 yrs (mean ± SD). Setting: Department of Obstetrics and Gynecology. Inclusion: newly delivered healthy women; well integrated in the Swedish language with uncomplicated vaginal delivery; painful postpartum uterine contractions that required pain relief. Exclusion: systemic disorders; abnormal pregnancy; operative delivery; other treatments for the pain should not have been initiated. Withdrawals/dropouts: 1 in HI TENS group dropped out due to discomfort of stimulation.
Interventions	Where applied: in hospital. Applied by: clinician. Waveform: not detailed. Frequency: 80 Hz. Pulse duration: 0.2 ms. Pulse amplitude/Intensity: HI, set at 50 mA. LI, set at just above the sensory threshold (10 to 15 mA). Electrodes: 2 carbon rubber and gel, 53 x 34 mm, placed on the lower part of the abdomen, bilaterally over the uterus. Duration and frequency of Rx: 1 minute, 1 Rx repeated twice if no effect occurred. Device/manufacturer: Cefar AB, Lund, Sweden. Adverse effects: no adverse effects except for discomfort during stimulation were recorded.
Outcomes	Pain outcome: measurement of discomfort on a 5‐point verbal scale, before and after Rx.  VAS for present pain intensity, before and after Rx. Discomfort of Rx recorded on a 5‐point verbal scale. ITT/per protocol analysis: not detailed. Statistical analysis: median decrease in VAS pain ratings before and after treatment was larger in the HI TENS group than in the LI TENS group. Post Rx, women in the HI TENS group had less pain from the uterine contractions than the women in the LI TENS group. HI TENS group experienced significantly less discomfort from uterine contractions after treatment compared with the LI TENS group. Discomfort from TENS itself was significantly greater in HI group than in LI group.
Notes
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Low risk	"After informed written consent, the women were randomised to either high‐intensity (HI) or low intensity (LI) high‐frequency (80 Hz) TENS. The allocation sequence was determined before the study by a research assistant using a computer generated random table."
Allocation concealment (selection bias)	Low risk	"Groups were coded and the allocation transferred to a series of pre‐sealed opaque envelopes."
Incomplete outcome data (attrition bias) All outcomes	Low risk	"One patient in the HI TENS group dropped out from the study immediately after commencing TENS treatment because of discomfort of the stimulation."
Source of funding bias	Unclear risk	No details provided.
Blinding (Participant)	Low risk	Study described as single‐blind. Groups were high‐intensity (HI) or low intensity (LI) high‐frequency (80 Hz) TENS. There was no placebo TENS group. "Before treatment the women were informed that they might experience pain or discomfort from the electrical stimulation." Author response: "it was the participants who were blinded to the treatment". Author response: "The patients had no previous experience of TENS".
Blinding (Outcome Assessor)	High risk	Study was designed as single blind.
Sample Size	High risk	HI TENS (N = 13); LI TENS (N = 8).