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.     

Patterns of human fetal heart rate accelerations from 26 weeks to term

Computerized analysis of the distribution of 2598 fetal heart rate accelerations in 83 healthy fetuses at 26 to 40 weeks' gestation demonstrated that the currently used definition of an acceleration as greater than or equal to 15 beats/min for greater than or equal to 15 seconds is applicable only after 30 weeks' gestational age in fetuses with a basal fetal heart rate of less than or equal to 128 beats/min. A significant negative correlation was found between the mean hourly basal fetal heart rate and the mean amplitude of fetal heart rate accelerations from 30 weeks to term. There was also a significant maturational process in the pattern of fetal heart rate and fetal heart rate accelerations that occurred between 26 and 28 and between 30 and 32 weeks; this was characterized by a decrease in basal fetal heart rate, an increase in the amplitude of fetal heart rate accelerations, and an increase in long-term fetal heart rate variability.     

Longitudinal measurements of fetal breathing, body movements, heart rate, and heart rate accelerations and decelerations at 24 to 32 weeks of gestation

Fetal breathing, fetal body movements, fetal heart rate, and fetal heart rate accelerations and decelerations were studied longitudinally in healthy fetuses between 24 and 32 weeks' gestation in the second and third hour following an 800 kcal maternal meal. The expected increase in fetal breathing following a maternal meal was not seen until fetuses were at 30 to 32 weeks' gestation. The number of body movements decreased and the interaction between body movements and fetal heart rate accelerations became more evident as fetuses became older. Fetal heart rate decelerations increased with gestational age, and the relative proportion of total decelerations that were either associated with body movements or were part of a deceleration/acceleration/deceleration complex increased from 24 to 32 weeks' gestation. The data support the hypothesis that gestational age is an important variable to consider when interpreting biophysical measurements in the human fetus at 24 to 32 weeks' gestation. Fetal body movements may be the single most important measurement of fetal health at these gestational ages.     

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.     

Relationship between fetal heart rate and umbilical blood flow velocity in term human fetuses during labor

Fourteen pregnant women between 37 and 41 weeks' gestational age, who subsequently were delivered of healthy newborn infants, were studied to examine the effects of spontaneous changes in fetal heart rate on the flow-velocity waveforms in the umbilical artery. The women were in active labor and under epidural anesthesia at the time Doppler measurements were made. There was a significant positive relationship between end-diastolic flow velocity and fetal heart rate. The umbilical artery peak-systolic/end-diastolic ratio was best correlated with the negative reciprocal transformation of the instantaneous fetal heart rate value and end-diastolic flow velocity. No significant correlation was found between fetal heart rate, umbilical artery peak-systolic/end-diastolic ratio, and peak-systolic flow velocity. An upper limit of 3.0 for a normal umbilical artery peak-systolic/end-diastolic ratio was acceptable only if the instantaneous fetal heart rate was greater than or equal to 130 beats/min.     

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.     

Clinical aspects of fetal heart auscultation

The widespread belief that fetal heart tones are first detected with an unamplified fetoscope at about 20 weeks' gestation has been studied prospectively only twice. Using data collection prospectively from 352 visits of 77 patients between 15 and 23 weeks' pregnancy, we studied various clinical aspects of fetal heart tone detection. We determined the gestational age at the time of initial auscultation of fetal heart tones with an ordinary fetoscope, and its relationship to quickening, parity, and placenta location. Fetal heart tones were first identified by auscultation at a mean gestational age of 19.4 weeks (range 17-22 weeks). Detection was possible in 81% of patients examined at 20 weeks and in virtually all patients examined at 21 weeks or later. Once heard, fetal heart tones were identified in every subsequent visit for all patients. Parity and placenta location were significant factors influencing initial fetal heart tone detection. Auscultation preceded quickening in only 12% of patients. Recommendations for using initial fetal heart tone detection in clinical practice are given.     

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.     

Transient non-autoimmune fetal heart block

OBJECTIVES: Fetal heart block is a rare and irreversible condition associated with structural heart defects or maternal autoantibodies (SS-A/Ro and SS-B/La) resulting in permanent damage of the atrioventricular (AV) node. This is the first report of 4 cases with a transient fetal heart block in structurally normal hearts without maternal autoantibodies. METHODS: A report on 4 patients seen within a 14-year period at one center with fetal heart block without intracardiac abnormalities or maternal autoantibodies. RESULTS: Three patients were referred to our center with a fetal bradycardia (heart rate 70-85 bpm), between 20 and 33 weeks' gestational age, and 1 for a 'triple' test at 16 weeks' gestational age. Echocardiography showed a complete heart block in 2 fetuses, and a second-degree AV block in the other 2. Heart block had completely resolved at all following visits. Postnatal ECG recordings showed normal sinus rhythm in all patients. Echocardiographic evaluation at presentation and follow-up showed normal cardiac anatomy, without signs of hydrops or cardiac decompensation in all patients. All mothers tested negative on SS-A/Ro and SS-B/La autoantibodies. CONCLUSIONS: Fetal heart block can occur in the absence of structural heart defects and maternal autoantibodies to SS-A/Ro and SS-B/La. The origin of such heart block is unknown, but its course seems benign: none of the patients ever showed ventricular heart rates <55 bpm, signs of congestive heart failure or fetal hydrops. Heart block resolved spontaneously in all patients.     

Relationship between cyclic variation of fetal heart rate patterns and cord pH in preterm gestations

The presence or absence of cyclic variation (cyclicity) of fetal heart rate patterns was prospectively investigated in fetuses between 25 and 32 weeks' gestation. All fetuses were delivered by cesarean section before the onset of labor. The relationship between the presence or absence of fetal heart rate cyclicity and fetal acidosis, as determined by cord pH measurements, was investigated. The sensitivity, specificity, positive predictive value, and negative predictive value of this method in predicting fetal acidosis were: 100, 90, 50, and 100%, respectively. All fetuses with reactive nonstress tests also had fetal heart rate cyclicity present and none were acidotic at birth. The majority of fetuses (68.8%) with nonreactive nonstress tests had fetal heart rate cyclicity present and none were acidotic; fetuses with nonreactive nonstress tests and absence of fetal heart rate cyclicity were acidotic in 50% of the cases. These preliminary data suggest that the presence or absence of fetal heart rate cyclicity may help to select the healthy preterm fetuses with nonreactive nonstress testing who are in good condition and therefore in no need for further testing.     

The relationship between movements and accelerations in fetal heart rate at twenty-four to thirty-two weeks' gestation

The purpose of this study was to establish the relationship between fetal heart rate accelerations and fetal body movements in fetuses at 24 to 32 weeks' gestation. The results suggest that body movements in younger fetuses do not occur with accelerations that are readily recognizable (i.e., less than 15 bpm), but as fetuses get older, the interaction between body movements and fetal heart rate becomes more evident and accelerations become more recognizable (i.e., greater than or equal to 15 bpm). The data presented suggest that there is a maturational aspect to the relationship between fetal heart rate and fetal body movements as fetuses increase in gestational age from 24 to 32 weeks. The conclusion, therefore, is that the nonstress test, as presently defined for older fetuses, is not valid for gestations below 32 weeks, and new criteria must be established.     

Autonomic nervous system regulation of baseline heart rate in the fetal lamb.

OBJECTIVE: We examined 29 chronically instrumented fetal lambs from 125 to 143 days' gestation to investigate the effects of fetal behavioral states and autonomic nervous system maturation on baseline fetal heart rate. STUDY DESIGN: Behavioral states were defined from electrocorticographic analysis as low-voltage fast activity or high-voltage slow activity. Decrease and increase in baseline fetal heart rate subsequent to administration of propranolol and methylatropine represented beta-sympathetic and parasympathetic activity. RESULTS: Baseline fetal heart rate decreased with gestation in both states, with steeper regression in low-voltage fast activity (p less than 0.001). Positive correlation was noted between gestational age and percent decrease baseline fetal heart rate in both states with steeper regression in high-voltage slow activity (p less than 0.001), and between gestational age and percent increase baseline fetal heart rate with steeper regression in low-voltage fast activity (p less than 0.001). Fetal heart rate beta-sympathetic and parasympathetic tones increased with age in both states, with elevation of beta-sympathetic tone in high-voltage slow activity and parasympathetic tone in low-voltage fast activity. CONCLUSION: Sympathetic and parasympathetic systems influence baseline fetal heart rate in these behavioral states and with age.     

Human fetal ductal flow velocity waveforms relative to behavioral states in normal term pregnancy

In 16 normal pregnancies the relationship between the blood flow velocity waveform and fetal behavioral states at 37 to 38 weeks' gestation was studied. Whereas behavioral state independency was established for the acceleration time, peak flow velocity demonstrated a statistically significant reduction during active sleep, compared with quiet sleep. These data reflect reduced ductal flow and suggest a redistribution in the left-ventricular and right-ventricular output in favor of the left side of the heart during active sleep. Peak flow velocities in the fetal ductus arteriosus were independent of fetal heart rate.     

Trends in continuous metabolic monitoring during experimental fetal distress

Intermittent, progressive maternal aortic occlusions were used to produce fetal distress in the fetuses of six pregnant dogs at term. Fetal heart rate and fetal tissue surface pH were continuously recorded and were compared to fetal blood pH, pCO2, pO2 and lactic acid values determined from intermittent sampling. Baseline fetal heart rate was an insensitive indicator of fetal blood pH, tissue surface pH, or of fetal blood lactic acid concentrations. "Delayed" decelerations in fetal heart rate following an occlusive episode were uniformly produced after minimal stress and also did not correlate well with these variables. On the other hand, fetal blood lactic acid concentrations remained elevated even after occlusive episodes were discontinued and other variables had returned to baseline values.     

Correcting umbilical artery flow velocity waveforms for fetal heart rate is unnecessary

We prospectively examined 55 normal pregnant women between 32 and 41 (means = 37) weeks' gestation. Five measurements of the umbilical artery peak-systolic/end-diastolic frequency ratio were obtained from each patient during one examination. Comparison of the fetal heart rate and the umbilical artery peak-systolic/end-diastolic frequency ratios between pregnancies less than 37 and greater than 37 weeks' gestation revealed no difference. Subsequently a total of 256 measurements were analyzed as one group. Plotting the individual peak-systolic/end-diastolic frequency ratios against the corresponding fetal heart rates revealed a moderate negative linear correlation: y = 4.15-0.012x, r = -0.36 and p less than 0.04. When only heart rates between 120 to 160 beats/min were plotted against peak-systolic/end-diastolic frequency ratios, a weaker correlation was found (r = -0.33, p = 0.15). The difference (mean +/- SD) between the obtained and the corrected peak-systolic/end-diastolic frequency ratios was 4.4% +/- 3.2%. The 95th percentile of the obtained peak-systolic/end-diastolic frequency ratio was 3.35 and the corrected ratio was 3.27. Averaging of the five measurements obtained from each patient for all 55 patients decreased the 95th percentile value to 3.09 whereas the same procedure for the corrected peak-systolic/end-diastolic frequency ratios decreased it to 3.07. We conclude that although there is a statistically significant negative linear correlation between the fetal heart rate and the umbilical artery peak-systolic/end-diastolic frequency ratio, this relationship is not clinically significant.     

Sinusoidal rhythm caused by fetal hemorrhage during fetoscopy

The sinusoidal fetal heart rate pattern has been reported to be associated with fetal anemia, hypoxia, administration of alphaprodine while, in other cases, it has been followed by good fetal outcome. In this case study fetoscopy was performed in a patient with thalassemia trait for prenatal diagnosis of thalassemia. Following the insertion of the trocar, bloodstained amniotic fluid was aspirated which resulted to be all fetal in origin. Estimation of feto-maternal hemorrhage was 5.7 ml while the amount of intra-amniotic bleeding could not be assessed. Fetal heart rate, which was recorded throughout fetoscopy, showed a sinusoidal pattern starting two minutes after the fetal hemorrhage which lasted more than ten minutes. Two hours later the fetal heart rate was normal. The pregnancy continued uneventfully and a healthy female baby weighing 3100 g was delivered at 38 weeks' gestation. Review of the literature suggests that a sinusoidal pattern may be caused either by a hemodynamic disturbance or fetal acidosis. In any case it does not always indicate impending fetal death.     

Intracranial pressure and fetal heart rate patterns in a case of hydrocephaly

A hydrocephalie fetus at term was studied during labor by means of direct continuous fetal heart rate, intracranial and intra-uterine pressures. Baseline instantaneous fetal heart rate pattern was characterized by periodic accelerations and increased short-term variability. This pattern was unchanged despite insertion of an intracranial catheter and instillation of isothermic saline. Atropine, given to the mother, produced a marked rise in fetal heart rate and a decrease in variability. Intracranial pressure, before and after decompression, always exceeded intrauterine pressure.After cranial decompression, typical, terminal fetal heart rate changes were noted, probably due to acute intracranial damage with secondary hypoxia. Theoretical and clinical implications of these observations are discussed. Specific fetal heart rate changes in hydrocephalic fetuses are not definable at this time.     

Defining altered fetal growth by second-trimester sonography

A method of predicting birth weight from a single ultrasound examination between 18-28 weeks' gestation was evaluated prospectively in 315 obstetric patients with singleton pregnancies. Estimated fetal weight at the time of the ultrasound examination was used to predict actual birth weight. At delivery, the percent difference between the projected and actual birth weights was then used to define whether an infant was small, appropriate, or large for gestational age. This method appeared to be accurate and showed identical relationships to the presence of abnormal fetal heart rate patterns in growth-retarded infants as did the traditional birth-weight-for-gestational-age method of defining intrauterine growth retardation.     

Characterization of fetal body movement recorded by the Hewlett-Packard M-1350-A fetal monitor.

OBJECTIVE: The purpose of this study was to evaluate the ability of a commercially available monitor, the Hewlett-Packard M-1350-A fetal monitor, to record and discriminate between various fetal body movements. STUDY DESIGN: Twenty-four patients between 29 and 42 weeks' gestation were monitored over a 20 to 30 minute period simultaneously by the Hewlett-Packard instrument and ultrasonography. RESULTS: All 593 single or clustered fetal movements recorded by the monitor were seen ultrasonographically as being extremity movements that were either isolated or combined with trunk motion. Discriminating between these two types of movements was not possible on the basis of the duration of recorded movements. All adequate fetal heart rate accelerations were attributed to combined trunk and extremity movements. Detection of fetal hiccups was less exact, and recording of fetal hand, mouth, breathing, and rapid eye movements was beyond the sensitivity of the monitor. Signal artifacts were attributable to either motion of the maternal abdomen or Doppler transducer and became less of a problem with experience. CONCLUSION: Fetal extremity movements were recorded with accuracy by this new fetal monitor.     

Intrapartum fetal heart rate monitoring in cases of cytomegalovirus infection

OBJECTIVE: Several studies have shown that abnormal intrapartum fetal heart rate patterns are the results from pre-existing fetal brain damage. We evaluated intrapartum fetal heart rate pattern of cytomegalovirus-infected fetuses and correlated the patterns with neurologic outcomes. STUDY DESIGN: Between 1991 and 2001, there were 20 cytomegalovirus-infected fetuses. We selected 40 fetuses as control subjects that were matched for gestational age and birth weight. Fetal heart rate was interpreted according to the guidelines of the National Institute for Child and Human Development. The incidence of abnormal fetal heart rate pattern and umbilical blood gases were compared between both groups. We also investigated the factors that contributed to abnormal fetal heart rate pattern in the cytomegalovirus group. RESULTS: Nonreassuring fetal heart rate patterns (prolonged deceleration and recurrent late deceleration) were observed in 8 of 20 fetuses (prolonged deceleration, 7 fetuses; recurrent late deceleration, 1 fetus) in the cytomegalovirus group and in 3 of 41 fetuses (prolonged deceleration, 1 fetus; recurrent late deceleration, 2 fetuses) in the control group (P<.05, Fisher test). Baseline fetal heart rate variability was minimal in 4 of the 7 prolonged deceleration cases in the cytomegalovirus group. Umbilical pH <7.1 was found for 1 fetus in the cytomegalovirus group. The average umbilical arterial pH values were similar in both the groups. In the cytomegalovirus group, there were no differences in the incidence of contributing factors between 8 fetuses with abnormal fetal heart rate pattern (prolonged deceleration and recurrent late deceleration) and 8 fetuses with no change. There were 3 fetuses with cerebral palsy: 2 fetuses in the no change group and 1 fetus in the prolonged deceleration group. Antigenemia was positive exclusively in 4 cases with abnormal fetal heart rate pattern (P<.05). CONCLUSION: Cytomegalovirus-infected fetuses are more likely to show abnormal intrapartum fetal heart rate patterns than low-risk control fetuses, which suggests that the perinatal detection of cytomegalovirus is necessary to distinguish hypoxic-ischemic encephalopathy.