--- title: "Fetal Vibroacoustic Stimulation for Fetal Assessment" url: https://alsuprun.com/blog/vibroacoustic/fetal-vibroacoustic-stimulation-for-fetal-assessment/ author: "Editorial" date: 2026-10-01T15:04:11+00:00 categories: ["vibroacoustic"] tags: [] --- # Fetal Vibroacoustic Stimulation for Fetal Assessment ## Background Fetal heart rate monitoring can be difficult to interpret when the baby is resting. This may lead to falsely nonreactive tests, which can result in unnecessary obstetric intervention. Extra tests, such as vibration and sound stimulation, are available to increase the likelihood that a baby is in difficulty and will respond to the test. However, it is important that such tests do not add to the risk of the procedure and do not increase the time the test takes to carry out. The aim of this study was to investigate whether a [vibroacoustic](https://alsuprun.com/) stimulus could be used as an alternative to a standard CTG trace in the assessment of fetal well-being in labour. The results of this work indicate that the use of this simple device could improve the ability to detect FHR accelerations during a nonreactive test, potentially reducing the risk and cost of unnecessary obstetric interventions. A modified acoustic stimulator was used to present the stimulus in the magnetic field of an MR scanner. The vibrating head of the stimulator was replaced with a coiled loop, which was mounted upon a plastic diaphragm and connected to an in-house built amplifier sited distant from the MR scanner magnet. This amplifier was controlled by the output signal of the main body of the acoustic stimulator, so that the stimulation amplitude varied with fetal orientation. The acoustic stimulus spanned the range in which maximum human hearing thresholds are found, with the sensitivity being lowest at the frequencies corresponding to the highest acoustic power. [![Rejuvenate your whole body & balance your health without medications - now remotely!](https://alsuprun.com/blog/wp-content/uploads/BioresonanceTopAd.png)](https://www.bioresonance.rent) The acoustic stimulus was presented for periods of 4 sec interspersed with 16 sec without the stimuli being applied. A relatively long TR was chosen to reduce scanner noise and to allow the fetus sufficient opportunity to habituate to the presence of a new sound stimulus. An EPI gradient was used to minimise movement induced by the change in magnetic field, and 180 images were acquired before presentation of the paradigm. The low sensitivity of the adult acoustic fMRI experiment, compared with previous reports in the literature, may be due to greater adult habituation to this simple acoustic stimulus, or to the use of a body coil rather than a birdcage coil for adult scanning (to mimic fetal MR scanning conditions). In either case, the relatively lower sensitivity observed could be improved using a head-coil or quadrature RF array system. ## Methods Fetal [vibroacoustic stimulation](https://alsuprun.com/) (VAS) is a simple, noninvasive test that involves placing a small vibrating probe on the maternal abdomen over the region of the fetal head and emitting a low-level sound for several seconds. The stimulant is thought to provoke a startle response in the fetus and produce a measurable cardiac tachycardia or acceleration on the cardiotocograph (CTG) trace. It is proposed that this can help reduce the false negative rate of nonstress tests and increase sensitivity to abnormal fetal heart-rate patterns, which are difficult to interpret. [![](https://alsuprun.com/blog/wp-content/uploads/ForeverYoungYouWannaBe.png)](https://alsuprun.com/services.html#Contact) In the current study, a modified stimulator was used to generate a single-pulse acoustic stimulus at an average intensity of 85 dB and a repetition rate of 3.5 Hz. This was chosen because it is a lower level of vibration than the original stimulus used in previous fMRI studies of adult subjects and thus may not cause any significant physiological perturbation to the pregnant subject. To ensure that the acoustic signal could be isolated from any electromagnetic interference, the scanner was equipped with a body coil. To further minimize any potential effects of acoustic stimulation on the BOLD signal, the amplitude of the stimulus was kept below a threshold value that has been shown to have no effect on fetal blood flow or oxygenation in the brain. This threshold was chosen to be close to the average amplitude of the acoustic signal measured on the fetal heart monitor during VAS in this pregnancy, which is estimated at about 50 dB. Results showed that a small but significant change in feto-maternal hemodynamic responses was observed after the stimulus and lasted for a few seconds. The time to peak of this hemodynamic response, or the fetal hemodynamic response (HDR) was measured for all the fetuses and adult study participants. An average ttp value was found for the fetuses of 7.36 +- 0.94 sec and for adults of 6.54 +- 0.54 sec. This reflects the fact that the stimulus intensity was relatively consistent for the adult and fetus groups, but it is unclear whether this difference is due to variations in the acoustic stimulus intensity or to differences between the fetal and adult study populations. ## Results Fetal [vibroacoustic stimulation](https://alsuprun.com/) (VAS) is a non-invasive technique used during labour to detect fetal well-being. It involves placing the device on the maternal abdomen over the region of the fetus and emitting sound at a predetermined level for several seconds. The resulting fetal startle reflex and a consequent acceleration or transient tachycardia of the fetal heart rate are believed to provide reassurance that the fetus is unimpaired. VAS has a high specificity but poor sensitivity. It is possible that a more sophisticated fMRI approach could improve the detection of a fetal response to this stimulus, and this study has been designed with this aim in mind. Seventeen pregnant women at more than 36 weeks gestation who attended antenatal clinics were recruited for this study. The fMRI scanning was carried out at 0.5 T to avoid susceptibility artefacts caused by current switching and magnetic field distortions in the abdominal area due to gas interfaces such as bowel gas, which can interfere with fMRI studies of responses to sound [Edwards and Martin, 1999]. Two fetal subjects were not analyzed because of problems relating to current artefacts overlaying on the VAS device and one case was not analysed because of a reluctance to perform a caesarean section when a reassuring biophysical profile score result was obtained (Table 1). Analysis of the remaining 17 fetuses showed that activation was localized in the temporal lobe in seven of the subjects; the other eight did not show any significant activation. The 13 adult participants also showed an activation in the temporal lobe (P 0.05). [![](https://alsuprun.com/blog/wp-content/uploads/RadionicMerch.png)](https://alsuprun.com/merch.html) Independent t-tests reveal that the fetuses show a significantly greater HDR than the adults. It should be borne in mind that the adult fMRI experiment was performed under conditions similar to those used for the fetal experiments and that adults are known to habituate rapidly to a simple acoustic stimulus [Bauer et al., 1997; Devoe et al., 1990; Gagnon et al., 1989; Kiuchi et al., 2000; Visser et al., 1989]. It is also worth mentioning that the acoustic stimuli in this study are within the frequency range for which maximum sensitivity in the human ear is attained. It is possible that this might explain why the adults showed relatively little response, although a difference in adult HDR might also be a consequence of the more rapid habituation observed in this population. ```json { "@context": "https://schema.org", "@type": "Article", "headline": "Fetal Vibroacoustic Stimulation for Fetal Assessment", "url": "https://alsuprun.com/blog/vibroacoustic/fetal-vibroacoustic-stimulation-for-fetal-assessment/", "datePublished": "2026-10-01T15:04:11+00:00", "dateModified": "2026-10-01T15:04:24+00:00", "author": { "@type": "Person", "name": "Editorial" }, "publisher": { "@type": "Organization", "name": "Information Wellness Blog", "url": "https://alsuprun.com/blog/" } } ```