Tongsong 1994.

Methods	Randomisation: randomisation method unknown. Effectiveness of randomisation was assessed by comparisons of several parameters within the 2 groups which include maternal ages, gestational ages and primary indications. All the FHR tracings were interpreted blindly by 1 independent perinatologist, who did not have any clinical information on the group of women.
Participants	Women of least 28 weeks' gestation with indications including postterm pregnancy, intrauterine growth retardation, pregnancy‐induced hypertension, chronic hypertension, decreased fetal movement and diabetes mellitus. Country: Thailand. 1273 women randomised.
Interventions	Women randomised to fetal acoustic stimulation group were given fetal acoustic stimulation for 1 second. If no qualifying acceleration was observed within 15 seconds, the stimulus were repeated up to 3 times. If reactive criteria were not achieved in 10 minutes, a new cycle of stimulation was begun. If both the women in the acoustic stimulation and standard non‐acoustic stimulation groups did not meet the reactive criteria within 20 minutes of the tests, the same technique was extended another 20 minutes.
Outcomes	Primary outcome: FHR reactivity. This was defined by the presence of 2 FHR accelerations or more of greater than 15 bpm and of 15 seconds' duration within a 20‐minute period. 1 prolonged acceleration of the FHR of at least 15 bpm lasting more than 2 minutes was also interpreted as reactive. If these criteria were not met in 40 minutes of monitoring, the test was interpreted as non‐reactive.
Notes	All acoustic tests were performed in the Maternal Fetal Medicine Unit by a specially trained physician with the woman in semi‐Fowler's position. Transabdominal acoustic stimulation overlying the fetal vertex was accomplished with an electronic fetal larynx of approximately 80 db and frequency of 80 Hz and a stimulation duration of 1 second. Randomisation was done after informed consent.
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Unclear risk	Randomisation method unknown.
Allocation concealment (selection bias)	Unclear risk	Unclear.
Blinding (performance bias and detection bias) All outcomes	Low risk	All the FHR tracings were interpreted blindly by one independent perinatologist, who did not have any clinical information on the group of women.
Incomplete outcome data (attrition bias) All outcomes	Unclear risk	Unclear.
Selective reporting (reporting bias)	Unclear risk	Unclear.
Other bias	Unclear risk	Unclear.

bpm: beats per minute
 BPPS: biophysical profile score
 db: decibels
 FHR: fetal heart rate
 Hz: hertz
 NICU: neonatal intensive care unit
 NST: non‐stress test
 VAS: vibroacoustic stimulation