McLachlan 1991.

Methods	Randomised double‐blind, placebo‐controlled trial. Analysis for breasts rather than women.
Participants	197 engorged breasts from 109 women who were referred to the physiotherapist for treatment of breast engorgement. Exclusion criteria: spoken or written English insufficient for informed consent; breast implants.
Interventions	Intervention breast: Medtron model P300 ultrasound machine used with aquasonic ultrasound transmission gel as coupling agent. Intensity was adjusted to give a comfortable warmth; application head massaged over breast towards areola; firmer pressure used on inwards stroke; duration of treatment ranged from 8 min for A cup to 15 min for a breast of DD or greater cup size. Control breast: ultrasound machine of identical appearance used in the same way as described above; the control machine had the crystal removed and replaced with a resistor to produce surface heat only. Participants were divided into 3 groups: group 1 (22 women) ‐ both breasts received ultrasound; group 2 (23 women) ‐ both breasts received sham treatment; group 3 (64 women) ‐ 1 breast received ultrasound and 1 breast received sham treatment.
Outcomes	Pain using a visual analogue scale, hardness using a visual analogue scale, hardness using a digital tonometer. Outcomes measured before and after treatment, prior to breastfeed.
Notes	Each breast, instead of an individual woman was the unit of analysis. The machines were labelled as A and B and were changed weekly by someone blind to allocation of women.
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Low risk	"Balanced block randomisation sequence."
Allocation concealment (selection bias)	Unclear risk	The authors do not mention allocation concealment.
Blinding (performance bias and detection bias) Women	Low risk	Women did not know which treatment they were getting. "The serial numbers of the machines were covered and the machines were labelled A and B. Labels were changed weekly by the Head of Department who had no role in the ultrasound treatment and did not hold the trial log book."
Blinding (performance bias and detection bias) Clinical staff	Low risk	"The serial numbers of the machines were covered and the machines were labelled A and B. Labels were changed weekly by the Head of Department who had no role in the ultrasound treatment and did not hold the trial log book. The woman's name was given to the clerical officer who held the trial log book. She informed the treating physiotherapist which machine to use. (A or B)."
Blinding of outcome assessment (detection bias)	Low risk	The outcome assessor was blinded to the groups the women were in.
Incomplete outcome data (attrition bias) All outcomes	High risk	The authors mentioned that 3 women were lost to follow‐up but they did not say how that was handled.
Selective reporting (reporting bias)	Low risk	The authors reported all the pre‐specified outcomes.
Other bias	High risk	Results were very difficult to interpret as analysis was by breast. The authors also state that when the visual analogue scale was used, it was not always easy for women to make a clear distinction between the left and the right breast.