Fetal response to vibratory acoustic stimulation in periods of low heart rate reactivity and low activity

The fetal response to vibratory acoustic stimulation during periods of low fetal activity and low fetal heart rate reactivity was studied in 10 healthy pregnant women at term. In each case, two periods of low reactivity were studied. Consecutive cases alternated: The vibratory acoustic stimulus was applied 10 minutes after the first nonreactive period in half of the cases; the remainder were stimulated during the second nonreactive period. The unstimulated period served as a control. After vibratory acoustic stimulation the baseline fetal heart rate, the mean number of fetal heart rate accelerations, and, the number of fetal movements were significantly increased with values in the control nonstimulated periods (p less than 0.0001). This consistent response to vibratory acoustic stimulation may prove to be clinically useful in altering periods of low reactivity observed during nonstress testing of normal fetuses.     

External vibratory acoustic stimulation near term: fetal heart rate and heart rate variability responses

Twenty-five pregnant women between 36 and 40 weeks' gestational age were studied to examine effects of a 5-second external vibratory acoustic stimulus on the fetal heart rate and fetal heart rate variability. There was an immediate significant increase in the basal heart rate, which persisted for 1 hour after the stimulus, compared to that of the control subjects. There was also a significant increase in the total time during which accelerations occurred for the first 20 minutes after the stimulus. There were no changes in computer-derived indices of fetal heart rate variability. Maternal blood pressure and heart rate were not altered following vibratory acoustic stimulus. We hypothesize that external vibratory acoustic stimulus causes a change from a state of sleep to a state of wakefulness in near term healthy fetuses.     

Effects of vibratory acoustic stimulation on human fetal breathing and gross fetal body movements near term

Twenty-five pregnant women between 36 and 40 weeks' gestational age were studied to examine effects of a 5-second external vibratory acoustic stimulus on fetal breathing and gross fetal body movement patterns. When the study period was compared with the control period, there was an immediate significant decrease in the incidence of fetal breathing movements that persisted for 1 hour after the stimulus. Moreover the fetal breathing pattern was more irregular for the hour after the stimulus. There was also a significant but delayed increase in the incidence of gross fetal body movements that persisted for 1 hour after the stimulus. We hypothesize that an external vibratory acoustic stimulus causes a change from a state of sleep to a state of wakefulness in near-term healthy fetuses.     

Preterm and term fetal cardiac and movement responses to vibratory acoustic stimulation

To assess fetal response to vibratory acoustic stimulation, 24 preterm (group A; less than 36 weeks' gestation) and 30 term (group B; greater than or equal to 36 weeks' gestation) pregnancies were studied. Study variables were perceived fetal movement, fetal heart rate, and fetal heart rate pattern. Observer- and patient-perceived fetal movement responses were noted in most cases but were slightly more common in term patients (group A: + fetal movement, patient 87.5%/observer 87.5%) group B: + fetal movement, patient 96.7%/observer 90%). Baseline changes in fetal heart rate (greater than or equal to 10 beats/min) were observed in 46% of preterm fetuses and 70% of term fetuses. Tachycardia (fetal heart rate greater than 160 beats/min) was a common finding in both groups. In group A, tachycardia after vibratory acoustic stimulation persisted more than 1 minute in 29.2% and more than 5 minutes in 12.5% of patients. In group B tachycardia beyond 1 and 5 minutes was noted in 73.3% and 50% of patients, respectively. A significant shift to "awake" fetal heart rate patterns occurred in both groups; 29% to 79% was noted in group A (p less than 0.001) and 46.7% to 90% in group B (p less than 0.001). When vibratory acoustic stimulation was used, the high occurrence of increased baseline, tachycardia, and emergence of unusual fetal heart rate patterns must be recognized to adequately interpret fetal heart rate tracings.     

Intrapartum vibratory acoustic stimulation of the human fetus during episodes of decreased heart rate variability

The effects of intrapartum vibratory acoustic stimulation during periods of decreased fetal heart rate variability were studied in 25 healthy term fetuses. Fetal monitoring and real-time ultrasound scanning were used simultaneously to detect fetal response. Vibratory acoustic stimulation was provided by an artificial larynx generating a signal at 85 dB and 85 Hz. This stimulus was applied for 5 seconds on the maternal abdomen over the fetal head after a 20-minute period of decreased fetal heart rate variability. All fetuses reacted with an immediate fetal heart rate acceleration of at least 10 bpm (range: 10 to 35 bpm, mean +/- SD = 18.4 +/- 7.0), and 19 fetuses also had sudden fetal body movement. A deceleration of the fetal heart rate after the initial acceleration was observed in nine fetuses (range: 15 to 70 bpm, mean +/- SD = 45.5 +/- 16.5). The implications of these findings are discussed in relation to the possible use of fetal vibratory acoustic stimulation for intrapartum surveillance.     

Influence of the fetal scalp electrode stimulation test on fetal heart rate and body movements in quiet and active behavioral states during labor

Thirty women were studied to examine the effect of fetal scalp stimulation on fetal heart rate (FHR) accelerations and gross body movements in quiet and active fetal behavioral states during the active phase of labor. Stimulation was performed by five consecutive tractions of the fetal scalp electrode. Fetal response in terms of fetal movements and FHR accelerations occurring within 15 seconds after stimulation was observed in all fetuses of the active state group. In the quiet state group 14 of 15 fetuses responded with body movements and in 12 fetuses FHR accelerations were observed. Subsequently, most of the fetuses returned to the quiet state. We suggest that a normal and healthy fetus is expected to respond to the fetal scalp electrode stimulation test even in the quiet behavioral state.     

Effect of the vibratory acoustic stimulation on fetal heart rate patterns of premature fetuses.

The purpose of this study was to examine the heart rate patterns before and after a standardized external vibratory acoustic stimulation in a group of 24 healthy premature fetuses at 32-35 weeks gestational age. FHR was analysed on line by Sonicaid Computer System 8000. A significant increase in the number of accelerations and an increase of variation after stimulus were observed. All other FHR patterns such as baseline, high and low episodes did not change significantly.     

Umbilical and uterine artery blood flow velocities after vibratory acoustic stimulation

Twelve healthy pregnant women between 37 and 41 weeks' gestational age were studied to determine the effects of external vibratory acoustic stimulation on the blood flow velocity waveform in the umbilical and uterine arteries. There was a significant decrease in umbilical peak-systolic/end-diastolic ratio during the first 5 minutes after stimulus after comparison with control ratios. Analysis of the frequency distribution of instantaneous fetal heart rate values during Doppler measurements suggested that the decrease in umbilical peak-systolic/end-diastolic ratio was due to fetal tachycardia rather than a change in the placental vascular resistance. The uterine artery peak-systolic/end-diastolic ratio was not altered after vibratory acoustic stimulation.     

The relationship between fetal activity and behavioral states and fetal breathing movements in normal and growth-retarded fetuses

The incidence of fetal breathing was studied during the course of behavioral state observations on 28 low-risk fetuses between 32 and 40 weeks' gestational age and on 12 growth-retarded fetuses between 36 and 40 weeks. Real-time ultrasound scanners were used to detect fetal eye, body, and breathing movements, and the fetal heart rate was recorded continuously. The mean duration of the observation sessions was 110 minutes. The mean incidence of fetal breathing was greater during periods of fetal activity (body and eye movements present, greater heart rate variability) than during quiescence (body and eye movements absent, narrowed heart rate variability) at all gestational ages studied in both low-risk and growth-retarded fetuses. During periods when one of the state variables (body movements, eye movements, heart rate pattern) was in its active condition while the other two were quiet, or the reverse, the incidence of fetal breathing was intermediate between those found when all three state variables were in agreement. After behavioral states had developed, at 38 and 40 weeks, the mean incidence of fetal breathing in the low-risk fetuses was greater during active states than during the quiet state. There was no apparent increase in the degree of linkage between fetal breathing and other expressions of fetal activity after the emergence of behavioral states.     

Stimulation of human fetuses with sound and vibration

Forty pregnant women between 30 and 42 weeks' gestational age were studied to examine the effects of external sound and vibration on the fetal heart rate. A significant increase in the mean duration and amplitude of the first acceleration after sound stimulus was found when these values were compared with the control values. Conversely the mean time to the first acceleration in the control period was greater than that in the stimulated period. There was a significant increase in the mean duration of fetal heart rate accelerations, the mean amplitude of fetal heart rate accelerations, and the total time spent in accelerations up to 15 minutes after the sound stimulus as compared with the control period. There was no change in the number of accelerations following the sound stimulus compared to control. These data suggest that vibratory acoustic stimuli may influence patterns of fetal heart rate during human pregnancy.     

Fetal heart rate and fetal activity patterns after vibratory acoustic stimulation at thirty to thirty-two weeks' gestational age

Twenty pregnant women between 30 and 32 weeks' gestational age were studied to examine the effects of a 5-second external vibratory acoustic stimulus on the fetal heart rate, fetal heart rate variability, and fetal activity patterns. There was an immediate significant increase in the basal fetal heart rate for 10 minutes compared with controls. There was also a significant increase in the mean duration of fetal heart rate accelerations without any change in the number of fetal heart rate accelerations. There were no changes in long-term fetal heart rate variability, fetal breathing, and gross fetal body movements.     

Evaluation of non-reassuring fetal heart rate patterns with fetal pulse oximetry combined with vibratory acoustic stimulation

Objective: To determine the value of fetal pulse oximetry and vibratory acoustic stimulation in the presence of non-reassuring fetal heart rate patterns during labor. Design: Prospective study in women monitored by cardiotocography and fetal pulse oximetry during labor. Materials and methods: During a period of 18 months, 907 consecutive parturients in labor were monitored by cardiotocography. Out of these women, 63 were selected on the basis of a non-reassuring fetal heart rate tracing during the first stage of labor. In these cases, fetal pulse oximetry was applied. Vibratory acoustic stimulation was applied in fetuses without spontaneous reactivity in order to evaluate the fetal status. Results: Our cases were classified into three groups, according to the lower fetal oxygen saturation levels, from the time of oximetry application until delivery. Group A consisted of 29 cases where fetal oxygen saturation levels were ≥41%, group B (20 cases) with fetal oxygen saturation of 31-40% and group C (14 cases) with levels of <30%. Spontaneous reactivity was observed in 15 fetuses of group A and seven of group B, while no case of reactivity was noted in group C. Vibratory acoustic-induced reactivity was associated with low fetal oxygen saturation levels. The mean umbilical artery pH levels were 7.29 ± 0.051 in group A, 7.21 ± 0.057 in group B and 7.04 ± 0.05 in group C. Conclusion: Fetal pulse oximetry should be indicated not only in fetuses without any reactivity but also in those with induced reactivity, after the application of vibratory acoustic stimulation.     

Ultrasonic imaging of normal fetal response to external vibratory acoustic stimulation

Fetal facial reactions and response decrement patterns to external noise stimulation were studied to characterize normal fetal neurobehavior in the third trimester. Response decrement, or habituation, is thought to reflect higher central nervous system function. Two hundred women with uncomplicated pregnancies, who were subsequently delivered of healthy infants at term, were studied between 26 and 41 weeks' gestation. After ultrasound views of the fetal face were obtained, a vibratory acoustic stimulus was applied repetitively to the maternal abdomen near the fetal head. Response decrement was defined as cessation of all components of the facial reaction, except eye blinking, over two sequential stimuli. Three response patterns were scored: (1) no startle, (2) startle without response decrement, and (3) response decrement by 12 stimuli. Whereas only 53% of fetuses between 26 and 27 weeks displayed startle reaction, all fetuses displayed startle responses by 28 weeks. As gestational age advances, an increasing number of fetuses exhibit response decrement, from no decrement at 26 to 27 weeks to 100% decrement at 40 to 41 weeks. A maturation of neurobehavioral response patterns takes place in normal third-trimester pregnancies. Response decrement testing may be a useful tool for in utero neurologic evaluation.     

The acoustic stimulation test in the anencephalus: preliminary results

It is not yet clear whether the acoustic stimulus influences the fetus by auditory or vibrational pathways. The anencephalic fetus is an interesting model for the study of the pathway for receipt of acoustic stimulation because of the near absence of cerebral hemispheres. After the traditional nonstress test (NST), the response to acoustic stimulation was assessed in eight fetal heart rate (FHR) recordings of six anencephalic fetuses of gestational age between 18 and 39 weeks. Although four preterm fetuses demonstrated nonreactive results in the NST, two term fetuses revealed reactive NSTs. However, none of these six anencephalic fetuses responded to acoustic stimulation. These data suggest that the cerebral cortex is the origin or transmission route of the FHR response to acoustic stimulation. We hypothesize that the normal fetus might receive externally applied sounds via auditory pathways rather than vibratory pathways, at least in term pregnancy.     

Behavioral State Organization in Human Term Fetuses: Evidence of Relatively Tight Control of State Cycling

Repeated alterations in episodes of quiet sleep (QS) and active sleep (AS) is a basic feature of behavioral state organization in human fetuses. Activation of the reticular formation (RF) is important in the transition from QS to AS, and intrinsic changes in central nervous system (CNS) activity govern RF activation. Vibroacoustic stimulation (VAS) can alter RF activation and thus delay the occurrence of QS. We hypothesize that if intrinsic RF activation in human fetuses is greatest just after entering AS and is decreasing as an AS-to-QS transition is approached, then fetuses ought to be in an active period longer if stimulated just after entering AS than if stimulated closer to an AS-to-QS transition. The purpose of this study was to test this hypothesis. We examined 87 normal human fetuses between 37 and 41 weeks of gestation. Behavioral states were assigned based on fetal heart rate pattern and the presence or absence of fetal eye and gross body movements. All fetuses were observed to enter AS before being randomized to a particular group. After remaining in AS for 3 min, the fetus either was not stimulated (N = 30), received a single 1-s VAS after 3-5 min of AS (N = 30), or received a single 1-s VAS after 44-46 min of AS (N = 27). Heart rate and eye and body movements were monitored continuously until the fetus either returned to QS and remained in that state for 3 min or did not return to QS within 60 min. All 57 fetuses who were stimulated in AS responded to VAS with gross body movement and an increase in heart rate, indicating that there was no effect of prestimulus state duration on the sensitivity to VAS. Fetuses stimulated after 3-5 min of AS behaved similarly to fetuses who had entered AS spontaneously. However, fetuses who were stimulated after being in AS for 44-46 min remained in an active period for a significantly shorter length of time following VAS than fetuses who either had been in AS for 3-5 min before VAS (19.6 min versus 36.4 min, P = 0.0001) or had entered AS spontaneously (19.6 min versus 44-2 min, P = 0.0001). When we included our results from a previous study examining state organization following VAS delivered in QS, we found that stimulation of the fetus around the time of a spontaneous AS-to-QS transition elicited a significantly different behavioral response than VAS delivered around the time of a spontaneous QS-to-AS transition: regardless of whether fetuses were in AS or QS at the time of stimulation, fetuses who were stimulated in close proximity to an AS-to-QS transition returned to QS sooner than fetuses who were stimulated closer to a QS-to-AS transition (18.7 min versus 37.2 min, P = 0.0001). We conclude that underlying changes in CNS activity, which continue to occur in the absence of overt behavioral changes, place relatively strict requirements on the amount of AS and QS during fetal life.     

Fetal heart rate and activity patterns in growth-retarded fetuses: changes after vibratory acoustic stimulation

Seventeen pregnant women who subsequently were delivered of infants with birth weights less than the third percentile were studied for examination of fetal heart rate and fetal activity patterns before and after a 5-second external vibratory acoustic stimulation. None of the fetuses was acidotic at birth. A reduced time was noted during which accelerations in heart rate occurred (50% less) and long-term fetal heart rate variability (25% less) in small for gestational age fetuses compared with age-matched, normally grown fetuses. The incidence of gross fetal body movements was significantly lower (40% less) in small for gestational age fetuses than in those who were appropriate for gestational age. Fetal heart rate and fetal activity patterns after stimulation with the electronic artificial larynx in small for gestational age fetuses were similar to those of appropriate for gestational age fetuses.     

Fetal acoustic stimulation in the early intrapartum period as a predictor of subsequent fetal condition

Fetal acoustic stimulation has recently received much attention in the literature. This study evaluates fetal acoustic stimulation in the early intrapartum period as a predictor of subsequent fetal condition. The study group consisted of 201 patients, approximately 60% of whom had complicated pregnancies. All were in the latent phase of labor with singleton, vertex-presenting fetuses. Gestational age ranged from 37 to 43 weeks. Fourteen of the 201 fetuses (7%) showed a nonreactive response to fetal acoustic stimulation and those fetuses were at significantly greater risk of initial and subsequent abnormal fetal heart rate patterns, meconium staining, and cesarean delivery because of fetal distress and Apgar scores less than 7 at both 1 and 5 minutes. Transient fetal heart rate decelerations after a reactive response occurred in 25% of patients; however, fetal outcome was not worse in this group. A reactive response to fetal acoustic stimulation was associated with high specificity and negative predictive values. Therefore we conclude that fetal acoustic stimulation in the early intraprtum period may discriminate the compromised from the noncompromised fetus.     

A comparison of fetal behaviour in breech and cephalic presentations at term.

OBJECTIVE: To evaluate fetal behaviour in breech and cephalic fetuses at term, using a computerised fetal behaviour program. DESIGN: An observational study. SETTING: Pregnancy Assessment Centre, University Hospital, Nottingham. SAMPLE: Twenty-six breech and 58 cephalic fetuses between 36 and 41 weeks. METHODS: Behaviour (fetal heart rate and activity) was recorded with the use of Doppler ultrasound. The duration of recording was 60 minutes or more in all but four recordings (minimum 49 minutes). MAIN OUTCOME MEASURES: Behavioural criteria studied were 1. the relative percentage time spent in low and high variation fetal heart rate patterns; 2. the duration and recurrence of fetal activity; 3. the number of accelerations in low and high fetal heart rate variation; and 4. the number of fetal behavioural state transitions. RESULTS: Breech fetuses differed from the cephalic group in that they were lighter than the cephalic fetuses (median 3105 g vs 3400 g; P < 0.01) and were born to older mothers (median maternal age 30 years vs 28 years; P < 0.01). No significant differences were found in rates of movement, numbers of accelerations and time exhibiting low and high fetal heart rate variation. However, breech fetuses exhibited significantly more state transitions (median 5.2/h vs 3.69/h; P = 0.01). CONCLUSIONS: This study shows that breech fetuses are neurologically different from their cephalic counterparts in otherwise healthy pregnancies, and that subtle behavioural differences can be demonstrated in utero using this computerised method.     

A comparison of fetal behaviour in breech and cephalic presentations at term

Objective To evaluate fetal behaviour in breech and cephalic fetuses at term, using a computerised fetal behaviour program.
Design An observational study.
Setting Pregnancy Assessment Centre, University Hospital, Nottingham.
Sample Twenty-six breech and 58 cephalic fetuses between 36 and 41 weeks.
Methods Behaviour (fetal heart rate and activity) was recorded with the use of Doppler ultrasound. The duration of recording was 60 minutes or more in all but four recordings (minimum 49 minutes).
Main outcome measures Behavioural criteria studied were 1. the relative percentage time spent in low and high variation fetal heart rate patterns; 2. the duration and recurrence of fetal activity; 3. the number of accelerations in low and high fetal heart rate variation; and 4. the number of fetal behavioural state transitions.
Results Breech fetuses differed from the cephalic group in that they were lighter than the cephalic fetuses (median 3105 g vs 3400 g;   P < 0.01  ) and were born to older mothers (median maternal age 30 years vs 28 years;   P < 0.01  ). No significant differences were found in rates of movement, numbers of accelerations and time exhibiting low and high fetal heart rate variation. However, breech fetuses exhibited significantly more state transitions (median 5.2h vs 3.69h;   P = 0.01  ).
Conclusions This study shows that breech fetuses are neurologically different from their cephalic counterparts in otherwise healthy pregnancies, and that subtle behavioural differences can be demonstrated in utero using this computerised method.     

Fetal responses to vibratory acoustic stimulation: influence of basal heart rate

Forty-three healthy pregnant women between 26 and 40 weeks' gestation were studied to determine the influence of prestimulation basal heart rate on the maximum amplitude of the first fetal heart rate acceleration after external vibratory acoustic stimulation. A significant negative correlation was found between the maximum amplitude of the first fetal heart rate acceleration and the prestimulation basal fetal heart rate from 30 weeks to term. In the presence of fetal tachycardia (basal fetal heart rate greater than 160 beats/min), more than 50% of fetal heart rate accelerations after stimulus were less than 15 beats/min amplitude. There was also a significant maturational process in the immediate fetal heart rate response to vibratory acoustic stimulation that occurred between 26 to 28 and 30 to 32 weeks characterized by a prolonged increase in basal fetal heart rate and an increase in the maximum amplitude of the first acceleration after stimulation.