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.     

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.     

The role of carbon dioxide in the generation of human fetal breathing movements

To determine the role of carbon dioxide in the generation of fetal respiratory movements, the effect of induced maternal hypocapnia and hypercapnia on fetal breathing movements, gross body movements, and fetal heart rate was studied in 12 healthy pregnant women near term. Patients were studied for a 1-hour control period breathing room air followed by four randomized 15-minute study periods with patients breathing either room air, a prepared gas mixture with 2% or 4% carbon dioxide, or undergoing controlled hyperventilation as determined by monitoring end-tidal PCO2. The percentage of time fetal breathing movements correlated significantly with maternal end-tidal PCO2 (r = 0.62, p less than 0.01), increasing with maternal breathing of 2% and 4% carbon dioxide and decreasing with maternal hyperventilation. Fetal gross body movements, fetal heart rate, and fetal heart rate variability showed no significant changes. It is concluded that as in adults, the carbon dioxide level in fetuses is an important stimulus for the generation of respiratory movements, acting independent of a change in behavioral state. It is hypothesized that tonic carbon dioxide level input is an important determinant of fetal respiratory center drive, but little or no phasic carbon dioxide input exists because of continuous placental excretion, thus resulting in the episodic occurrence of breathing movements with changes in the fetal behavioral state.     

Effect of naloxone on fetal behavior near term

Fetal behavior was studied after intravenous administration of either 0.4 mg of naloxone or an equal volume of saline solution in 54 healthy pregnant women near term. The number, duration, and amplitude of fetal heart rate accelerations increased after naloxone injection. The incidence of both gross fetal body movements and fetal breathing movements increased, especially in the first hour after naloxone administration. The distribution of fetal behavioral states was modified with a prevalence of active sleep and active awake states compared to the quiet sleep state. These data suggest that endorphins could be involved in the modulation of fetal behavior.     

Fetal breathing,gross fetal body movements,and maternal and fetal heart rates before spontaneous labor at term

In order to examine patterns of fetal breathing and body movements and fetal and maternal heart rates near term, we studied 28 healthy pregnant women over 24-hour observation intervals at 38 to 40 weeks' gestation. There was a significant decrease in the incidence of fetal breathing movements during the last 3 days before spontaneous parturition at term, but there was no significant difference in the patterns of gross body movements or fetal and maternal heart rates. We concluded that, prior to spontaneous labor at term, there is a normal decrease in the incidence of fetal breathing movements but no similar change in the incidence of gross fetal body movements. This study suggested that the presence of gross fetal body movements is a more consistent index of fetal health before spontaneous labor at term.     

Intrapartum fetal vibratory acoustic stimulation during spontaneous and induced states of low activity and low heart rate variability

Fetal response to vibratory acoustic stimulation (VAS) was studied in 12 healthy parturients in the active phase of labor. All fetuses were evaluated in both spontaneous and analgesia-induced states of low activity and low cardiac beat-to-beat variability. Analgesia was induced with intravenous maternal administration of meperidine, 0.8 mg/kg, plus a fixed dose of promethazine (25 mg). The vibratory acoustic stimulus was applied ten minutes after the start of a fetal quiet state, and ten minutes of fetal behavior was observed after application of the stimulus. The number and mean duration of fetal body movements in the unmedicated fetuses were statistically significantly higher than in the medicated group. Similarly, the number of fetal heart rate accelerations was significantly higher in the unmedicated fetuses than in the medicated ones. Ten minutes after VAS no fetus in the unmedicated group was in a quiet behavioral state, while 10 of 12 medicated fetuses (83%) returned to a quiet state.     

Intrauterine fetal activity in at term and prolonged pregnancies

Fetal body movements and breathing movements were recorded with a real time ultrasound scanner in 26 fetuses. There were two recording periods of 25 min each, before and half and hour after maternal IV administration of 50 gr glucose. Six fetuses were at 280 days of gestation (Group A), twelve fetuses were at 294 days of gestation (group B), eight fetuses at 294 days gestation were classified as stage I postmature (group C). The incidence of fetal body movements was not significantly different in the three groups. Maternal glucose administration had no significant influence on fetal body movements in any group. On the other hand fetal breathing activity was significantly increased in all three groups after maternal glucose administration. Breathing activity was significantly greater in group A when compared to group C in both recording periods, and when compared to group B in the period which followed maternal glucose administration. It is concluded that fetal breathing activity is reduced in prolonged pregnancies.     

Patterns of human fetal breathing activity at 34 to 35 weeks' gestational age.

Continuous measurements of human fetal breathing movements at 34 to 35 weeks' gestational age were made with an ultrasonic real-time scanner for periods of 24 hours in 11 women. A significant increase occurred in fetal breathing activity during the second and third hour following meals and this pattern apparently followed an increase in maternal plasma glucose concentration. There was a prolonged significant increase in fetal breathing activity between 0100 and 0700 hours. Increases in human fetal breathing activity accompanied by increased gross fetal body movements occurred for periods of 20 to 60 minutes out of every 1.0 to 1.5 hours of observation time. It was concluded that the percentage of time spent breathing by normal fetuses was related to time of day and maternal meals. The alternating changes of fetal activity and inactivity observed may represent biologic changes of sleep state in the human fetus in utero at 34 to 35 weeks' gestational age. It will be important to account for these three patterns of fetal breathing activity in clinical studies which examine the usefulness of fetal breathing movements in assessing fetal health.     

Human fetal breathing movements and gross fetal body movements at weeks 34 to 35 of gestation

Human fetal breathing movements in utero at 34 to 35 weeks' gestational age were measured using a real-time ultrasonic scanner. Fetal breathing movements were episodic and occurred 31.8 per cent of the time. Aanalysis of continuous recordings in 10 fetuses from 09:00 to 17:00 hours demonstrated that the percentage of time spent breathing per hour was greater in the afternoon than in the morning. The number of gross fetal body movements was also greater in the afternoon than in the morning. The percentage of time spent breathing was significantly greater during the hour following the noon meal than during the hour preceding the noon meal. It was concluded that real-time ultrasonic scanning permits identification of fetal breathing movements and that between 09:00 and 17:00 hours the character of these movements is related to the time of the day and to the ingestion of food by the mother.     

Human fetal breathing activity during electively induced labor at term.

Human fetal breathing movements were measured during the first stage of electively induced labor in 20 healthy term pregnancies. Fetuses made breathing movements 25.6% of the time during a 1 hour control period and breathing decreased significantly to 8.3% during latent-phase labor and further decreased to 0.8% during active labor (P less than 0.001). Patterns of increased fetal breathing activity accompanied by increased gross fetal body movements and increased fetal heart rate variability for periods of 20 to 60 minutes out of every 1.0 to 1.5 hours were observed, and the intermittent patterns of increased body movement and heart rate variability continued throughout the first stage of labor despite the decrease in fetal breathing activity during latent- and active-phase labor. It will be important to account for rest activity patterns when interpreting variability of heart rate during labor. The absence of fetal breathing activity during electively induced labor at term is not a clinical indicator of fetal ill health.     

Absent fetal movement response with a blunted cardioacceleratory fetal response to external vibratory acoustic stimulation in a fetus with the Pena-Shokeir syndrome (fetal akinesia and hypokinesia sequence).

We present a case that describes a partial fetal response to external vibratory acoustic stimulation in that, although no fetal movements were elicited, a blunted, brief positive cardioacceleratory response was noted. This fetus exhibited features of the Pena-Shokeir syndrome, characterized by skeletal neurogenic atrophy, yet with a normal auditory system at autopsy. This observation may suggest that the prolonged increase in the basal fetal heart noted after fetal vibratory acoustic stimulation is sustained by active fetal movements, absent in this fetus due to joint contractures.     

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.     

Combination of vibroacoustic stimulation and acute variables of mFBP as a simple assessment method of low-risk fetuses

Objectives. To observe a rate of fetal breathing and gross body movement appearance as physiologic reactions to the external vibroacoustic stimulation (VAS) and to establish a rapid and reliable antepartal method for accurate selecting of non-compromised fetuses in the low-risk population.

Methods. Actual condition of 742-term and near-term structurally normal and otherwise healthy singleton fetuses with favourable outcome was assessed by previously established combination of the modified fetal biophysical profile and VAS. Only inactive fetuses at the beginning of the testing were included in the study. The combined biophysical testing has been started by a transabdominal real-time ultrasound examination, followed by vibroacoustic stimulus applied over the fetal head for 5 s during fetal quiescence. Fetal breathing and gross body movements were observed with particular attention in each case at measured time intervals from the application of external VAS until the moment at which either the first 60-s episode of breathing movements or all three fetal gross body movements were detected. Obtained results have been presented numerically in 5-min periods and cumulative percentages.

Results. After the external VAS, 84.5% of studied fetuses successfully manifested their normal breathing or gross body movements in the first 5 min of the modified biophysical testing. Furthermore, approximately 96% of them were able to demonstrate at least one of these two biophysical activities after 6–7 min.

Discussion. Because of its simplicity, non-invasiveness, independence of precise gestational dating, reproducibility and immediate individual results, ultrasonographic observation of normal fetal breathing and/or gross body movements after the external VAS stands a real chance to become a nearly optimal antenatal test for accurate and rapid information of actual non-compromised fetal condition. Authors strongly believe that the described antenatal method should represent a rather efficient assessment procedure of fetal well-being in late pregnancy, performed during regular antenatal visits.     

Immediate effect of amniocentesis on fetal breathing and gross body movements

The incidence of fetal breathing movements (FBMs) has been observed to be significantly reduced at 24 and 48 hours after amniocentesis. The cause is unknown. We studied the immediate effects of amniocentesis on two fetal variables, FBMs and gross body movements (FMs). No effect was observed in the incidence of FBMs but an immediate increase in FMs occurred.     

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 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.     

Cigarette smoking and fetal breathing movements.

Cigarette smoking caused a reduction in the incidence of fetal breathing movements in normal and abnormal pregnancies. The size of the reduction varied, being greatest in small-for-dates pregnancies and pregnancies complicated by fetal distress in labour and least in pre-eclamptic pregnancies. The fall in the amount of fetal breathing movements was significantly related to the rise in maternal plasma nicotine after smoking but was unrelated to the rise in barboxyhaemoglobin. Smoking non-nicotine (herbal) cigarettes produced increases in carboxyhaemoglobin concentrations similar to those observed after smoking tobacco cigarettes, and was not associated with a fall in the incidence of fetal breathing movements. Chewing gum containing nicotine produced rises in plasma nicotine concentration similar to those observed after smoking tobacco cigarettes and was associated with a significant reduction in the incidence of fetal breathing movements. Hence nicotine appeared to be the factor in cigarette smoke responsible for the reduction in the incidence of fetal breathing movements. Nicotine was present in the cord blood of infants whose mothers smoked. The possible mechanism by which nicotine caused a reduction in the incidence of fetal breathing movements and its possible relevance to the detrimental effects of smoking on the fetus are considered.     

The effect of nicotine on fetal breathing movements in conscious pregnant ewes.

Nicotine (0.14--0.25 mg/kg), injected intravenously or intraarterially into conscious pregnant ewes, caused a decrease in fetal PaO2 within 5 minutes, persisting for up to 30 minutes. There was a significant fall in the incidence of fetal breathing movements. These changes did not occur if the ewe was treated with an alpha-blocking agent (phentolamine) or if the nicotine was infused for 30 minutes at 0.27 to 0.85 mg/minute. Nicotine crossed the placenta; fetal concentrations equaled those in the ewe 5 minutes after the injection and remained at or above maternal levels for 1 hour. Nicotine given directly to the fetus (0.005--0.03 mg/kg estimated fetal weight) stimulated fetal breathing movements in a dose-related manner. We suggest that the maternal injection of nicotine results in a fall of uterine blood flow by a sympathomimetic action, leading to transient fetal hypoxemia and a reduction of fetal breathing movements and that a similar phenomenon may occur when a pregnant woman smokes cigarettes.     

The effects of vibroacoustic stimulation on baseline heart rate, breathing activity, and body movements of normal term fetuses

To determine the fetal biophysical effects of vibroacoustic stimulation produced by an electronic artificial larynx we studied 20 normal term pregnancies assigned either to control (no stimulus) or experimental (stimulus) groups. Each fetus was observed for 3 hours; either no stimulus or a 3-second stimulus was delivered after the first hour. Fetal heart rate baseline and variation, breathing movement incidence, rate, and variation, and body movement incidence data were acquired concurrently and analyzed at 15-minute intervals. Intergroup comparisons showed that, after stimulation, fetal heart rate baseline and variation increased significantly, whereas breathing incidence fell during the first 15 minutes. Within-group analyses showed that poststimulus elevation of fetal heart rate baseline was the only significant time interaction over the 3 hours. Vibroacoustic stimulation appears to be primarily associated with transient alterations in fetal heart rate baseline; concomitant changes in breathing activity probably reflect normal biologic cycles.     

The effects of maternal hyperoxia on fetal breathing movements in third-trimester pregnancies

Fetal breathing movements and gross fetal body movements were observed before, during, and after maternal hyperoxia induced by inhalation of 50% oxygen in 14 women with normal term pregnancies. Studies were performed with real-time B-scan linear-array ultrasound and were standardized for time of day, maternal nutritional status, postprandial interval, and length of observation. Each study included a 30-minute baseline, followed by 15 minutes of hyperoxia, and 45 minutes of continued monitoring. No significant changes occurred in the mean incidences of fetal breathing movements, gross fetal body movements, the mean breathing rate, or breath interval variability, as analyzed in 5-minute epochs. Maternal PO2, as measured by transcutaneous electrodes, increased to the maximum level after 5 minutes of hyperoxia (155% over control levels). The breathing activity of normal third-trimester fetuses appears to be stimulated maximally in the second and third postprandial hours and cannot be further increased by maternal hyperoxia. This protocol represents a possible clinical strategy for investigating fetuses at risk for intrauterine hypoxia, provided that similar experimental conditions are maintained.