Marden 1997.

Methods	Randomisation: randomised by sealed envelopes with the use of a statistical package to generate the sequence of assignment.
Participants	Women of at least 31 weeks' gestation. Inclusion criteria included singleton pregnancy, intact membranes, and no concurrent use of magnesium or narcotics. Country: USA, Colorado. 577 women randomised.
Interventions	Women randomised to fetal acoustic stimulation group were given acoustic stimulation for 3 seconds with the stimulator placed at the midpoint between the maternal pubic symphysis and umbilicus. Fetal movements were palpated with the other hand at the fundus. Women randomised to control group were given mock stimulation for 3 seconds with the stimulator placed at the midpoint between the maternal pubic symphysis and umbilicus. Fetal movements were palpated with the other hand at the fundus.
Outcomes	Primary outcome: positive test as defined by palpation or visualisation of fetal movement only by the tester during a vibroacoustic stimulation. Other outcome: FHR reactivity.
Notes	The vibratory acoustic stimulus was performed using a vibroacoustic stimulator (Corometrics 146 fetal acoustic stimulator). Randomisation was performed after informed consent.
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Low risk	Randomisation with the use of a statistical package to generate the sequence of assignment.
Allocation concealment (selection bias)	Low risk	Sealed envelopes.
Blinding (performance bias and detection bias) All outcomes	Low risk	By performing the fetal acoustic stimulation test before NST, the tester was blinded to the result of NST.
Incomplete outcome data (attrition bias) All outcomes	Unclear risk	For 23 women, outcome data were not available. No further information provided.
Selective reporting (reporting bias)	Unclear risk	No outcomes documented in methods section.
Other bias	Low risk	No evidence of any other form of bias.