Antenatal cardiotocogram quality and interpretation using computers.

OBJECTIVE: To test the application in practice of computerized fetal heart rate (FHR) analysis in pregnancy. DESIGN: Randomized distribution of subjects with computerized analysis automatically revealed or concealed. SETTING: A district general hospital and a teaching hospital outside London. SUBJECTS: 2869 pregnant women studied within a year. OUTCOME MEASURES: Quality and duration of the cardiotocogram; quantitative measurement of FHR variation; number of stillbirths. RESULTS: With interactive advice to the operator, records were of improved quality (up to 28% without signal loss) with potentially much reduced recording time. The short-term FHR variation measured in the last records before intervention is reported for the first time. CONCLUSION: The benefits of using the computers include improvement in record quality and saving of time. In addition, where interpretation depended on estimation of FHR variation there was prima facie evidence of observer misinterpretation; visual analysis was unreliable. A larger trial is now required with more rigorous constraints on intervention.

The effects of pentobarbitone and pethidine on foetal breathing movements in sheep.

1 Small doses of pentobarbitone (4 mg/kg i.v.) administered to sheep in the last third of pregancy had little overt effect on the mothers. In the foetus they caused arrest of breathing movements, an alteration in the character of the electrocorticogram and cardiovascular changes which varied with gestational age. 2 In contrast, relatively large doses of pethidine (100-200 mg) admininstered to the mother had no consistent effect on normal foetal breathing movements, though they abolished the foetal response to hypercapnia. 3 The results are discussed in relation to feotal sleep state.

Short-term fetal heart rate variation, decelerations, and umbilical flow velocity waveforms before labor.

OBJECTIVE: To determine the value of computerized antepartum measurements of short-term fetal heart rate (FHR) variation and decelerations as a predictor of outcome, and to compare these with measurements of the umbilical artery flow velocity waveform. METHODS: Data were collected from 3563 high-risk patients for measurements of FHR variables (15,702 records) and outcome (intrauterine death or metabolic acidemia on delivery). Detailed analyses were made on 89 patients with one or more records in which short-term FHR variation was 3 milliseconds or less. Umbilical artery flow velocity waveforms were measured concurrently on 2441 occasions in 991 patients. RESULTS: More than half of the patients with FHR variation of 3 milliseconds or less were identified before 31 weeks. When short-term FHR variation exceeded 3 milliseconds, there were no intrauterine deaths and only one instance of metabolic acidemia on cesarean delivery. When FHR variation fell below 2.6 milliseconds, 34% of the subjects had metabolic acidemia on cesarean or intrauterine death. The appearance or absence of decelerations was an unreliable guide to outcome. The correlation between FHR variation and the umbilical artery flow velocity waveform was low (r = 0.32). The population studied contained some patients without placental vascular disease or, in five with pre-eclampsia, without abnormal umbilical artery velocity waveforms but with grossly reduced FHR variation. CONCLUSION: Reduction in short-term FHR variation, as measured by computer, reliably predicts fetal outcome and is a more general measure of fetal well-being than are umbilical artery flow velocities.

Approximate entropy, a statistic of regularity, applied to fetal heart rate data before and during labor.

OBJECTIVE: To determine whether approximate entropy (ApEn), a new statistic of regularity, when applied to fetal heart rate (FHR) data antepartum or in labor, would offer an advantage over standard statistics of variation in predicting outcome. METHODS: A large data base of antepartum FHR records collected in clinical practice over 10 years was available. Two data sets in labor were stored on disk in small computers interfaced to fetal monitors on-line. Outcomes were assessed using blood gas values on delivery and Apgar scores. RESULTS: Antepartum, when the most favorable form of ApEn was used on 769 good-quality FHR records, the correlation with measurement of short-term variation was high. This was especially true when the fetal pulse interval variation fell below the normal range (less than 6 milliseconds short-term; r = 0.93) and in 20 other records with sinusoidal variation (r = 0.96). Approximate entropy varied with fetal sleep cycles and took longer to calculate than FHR variation. During the last hour of labor, in 319 records, there was no significant correlation between umbilical artery base deficit values on delivery and ApEn measurement. In 871 additional good-quality records of fetuses with normal outcome, the mean (+/- standard error [SE]) ApEn (0.95 +/- 0.005) was significantly greater than in 22 records (0.88 +/- 0.028) from fetuses with abnormal outcome (umbilical artery base deficit more than 12 mmol/L and Apgar score of 3 or less at 1 minute). However, consideration of the frequency distributions of these measurements showed that ApEn did not discriminate between normal and abnormal outcomes. The SD of fetal pulse intervals rose in labor whereas ApEn values fell, confirming that this new statistic of regularity differs from standard statistics of variation. CONCLUSION: Approximate entropy offered no advantage over measurement of short-term FHR variation antepartum, and neither measurement predicted outcome in labor.

Computerized fetal heart rate analysis in labor.

Observer variation in visual analysis of fetal heart rate (FHR) records is reportedly high, but can be avoided by computerized numerical analysis. The FHRs of 394 women in labor at 37 or more weeks' gestation were recorded on-line and analyzed to examine how different patterns related to outcome, as judged by umbilical arterial base deficit or Apgar score on delivery. The range of normality and the diversity of patterns of those delivered without acidemia were great. Late decelerations were of poor prognostic value. There was an increase in FHR variation during labor averaging 40%. In this preliminary study, conventional attributes of the FHR, alone or in combination, did not predict metabolic acidemia. Epidural analgesia in 240 women was identified as a confounding variable that significantly affected FHR patterns without influencing the condition of the infant at birth. It was associated with a higher FHR, less FHR variation and fewer decelerations, primiparity, longer labors, more operative deliveries, and a threefold greater cesarean rate. The rise in basal FHR, perhaps due to a rise in maternal temperature, may partly explain the high intervention rate in those without fetal acidemia.

The influence of signal loss on the comparison between computer analyses of the fetal heart rate in labour using pulsed Doppler ultrasound (with autocorrelation) and simultaneous scalp electrocardiogram.

A comparison between the computer analyses of records of the fetal heart rate (FHR) obtained simultaneously by pulsed doppler ultrasound with autocorrelation and by fetal scalp electrocardiogram (ECG) in labour showed no statistical differences when signal loss was less than 2%. Increasing signal loss, due to maternal movement, correlated significantly with greater differences between ultrasound and ECG values for mean FHR variation (r = 0.58, p less than 0.005). With higher signal loss (average 15.6%) the mean FHR variation measured by ultrasound was significantly lower than that measured by ECG (T = 3.83, p less than 0.005) but this reduction was not of clinical significance.

The 1987 James A. F. Stevenson memorial lecture. The development of fetal behavioural patterns.

The development of fetal behaviour is reviewed. Fetal cutaneous and muscle sensory receptors are developed by the time movements are first seen. Human infants certainly respond to painful stimuli at 28 weeks. There is no clear evidence that prenatal "stress," e.g., maternal exposure to random noise and bright lights, impairs fetal development in the rat, on the contrary. Fetal diurnal rhythms appear in man and sheep before the development of sleep states; they are dependent on maternal corticosteroids, but the fetal mechanism is uncertain. With the development of sleep states (in late gestation in man and sheep, postnatally in the rat), the complex central control of behaviour is gradually established, but wakefulness is still of low incidence. The location of the sleep cycle generator is uncertain; the results of experimental lesions of the brainstem in fetal lambs appear incompatible with studies in adult rats and cats.

The central control of fetal breathing and skeletal muscle movements.

Breathing movements in the sheep fetus have been observed from a gestational age of about 40 days. From 95 to 115 days fetal breathing movements are almost continuous, interrupted by apnoea rarely exceeding 2 min. From 115 days until term (about 147 days) breathing and movements of the trunk and limbs are episodic. Breathing normally occurs only during rapid-eye-movement sleep as identified by low-voltage cortical electrical activity. Active movements of the neck muscles occur predominantly in high-voltage electrocortical activity. Hypercapnia or acid cerebrospinal fluid perfusion cause an increase in the regularity and depth of breathing when present, and recruit intercostal and laryngeal abductor activity. Isocapnic hypoxia, however, in contrast to the hyperventilation seen postnatally, causes arrest of fetal breathing movements. This effect is due to a central inhibition. Section of the brain stem, from the caudal hypothalamus rostrally, causes dissociation of fetal breathing movements and electrocortical activity into independent rhythms. Section of the brain stem caudally, in the upper pons or at the inferior colliculus, also causes a dissociation of electrocortical activity from breathing movements, which become almost continuous. Isocapnic hypoxia causes an increase in the rate and depth of breathing movements. It is concluded that the arrest of breathing in intact fetal lambs is not due to a direct effect on the respiratory centre in the medulla. The lumbar polysynaptic flexor reflex response becomes episodic after 115 days gestation but, in contrast to fetal breathing movements, is enhanced during high-voltage electrocortical activity. Isocapnic hypoxia arrests movements of the fetal limbs and trunk and inhibits the lumbar flexor reflex. This inhibition of the reflex is prevented by section of the spinal cord at T12, but persists after section of the brain stem in the upper pons. It is attributed to an action on the medulla, independent of the systemic arterial chemoreceptors. Small doses of pentobarbitone (5 mg/kg) cause arrest of fetal breathing movements by a suprapontine mechanism, abolished by brain stem transection, and inhibition of the lumbar flexor reflex by an action on the spinal cord, persisting after transection at T12. Inhibitors of prostaglandin synthetase (indomethacin, meclofenamate or aspirin) induce continuous fetal breathing movements, while prostaglandin E2 arrests fetal breathing. The site of action is on the medulla, as shown by section of the brain stem and of afferents from the systemic arterial chemoreceptors.(ABSTRACT TRUNCATED AT 400 WORDS)

The fetal ECG: accuracy of measurements.

Analysis of fetal heart rate is very dependent upon the accuracy with which fetal events can be timed. This depends upon signal quality and the type of processing used in signal analysis. Signal quality is affected by mode of recording and positioning of sensors. Signal loss can be kept to below 5% in routine clinical practice with appropriate attention to technique. Accuracy of beat-to-beat measurement needs to be 1 ms if short-term variability (epoch length 1/16 min) is to be assessed reliably.

Hypoxia and electrocortical activity in the fetal lamb: effects of brainstem transection and chemoreceptor denervation.

In order to investigate possible mechanisms for the effect of hypoxia on fetal electrocortical (ECoG) activity, the effects of 30 min of isocapnic hypoxia on ECoG were studied in three groups of unanaesthetized late-gestation fetal lambs in utero. One group was intact, in the second the brainstem was transected between the colliculi, and in the third the carotid sinus nerves and cervical vagosympathetic trunks were cut bilaterally to denervate the systemic arterial chemoreceptors. The incidence of high voltage (HV) ECoG activity was lower in brainstem-transected fetuses than in the other groups. All three groups showed an increased number of changes from low to high voltage and an increase in the incidence of HV activity at the onset of hypoxia, but the increases reached statistical significance only in the brainstem-transected group. It is concluded that the onset of hypoxia is often associated with an increase in HV ECoG activity, with the most consistent changes occurring after brainstem transection and similar but smaller increases in intact and denervated fetuses. Thus the response of fetal electrocortical activity to the onset of hypoxia does not depend on intact connections with the lower brainstem. However, the effect of hypoxia on fetal ECoG is minor and inconsistent and may be physiologically unimportant.

The association between cardiac accelerations and movements in fetal sheep.

Observations in 5 fetal sheep at 120-134 days gestation, using either real time ultrasound or direct emg recordings to detect fetal movements, showed an association between such movements and cardiac accelerations (greater than 2 s duration and 4 beats/min amplitude). Neuromuscular blockade with gallamine abolished the fetal movements but not the accelerations.

Improvements in the registration and analysis of fetal heart rate records at the bedside.

A microprocessor system is described for on-line analysis of the fetal heart rate detected by conventional Doppler systems. A brief account is given of the instrumentation and program structure. The system has been tested by analysing normal and abnormal antenatal fetal heart rate records. Pulse Doppler with autocorrelation measurement of the fetal pulse interval reduced the signal loss in clinical practice by a factor of 10, to an average of 2.1% in 629 records from uncomplicated pregnancies. Yet it is still necessary to identify signal loss, because it occasionally rises to unacceptable levels in association with fetal movements or hiccups. Medium-term measures of fetal heart rate variation (within 16-0.1 cycles/min) varied with gestational age, but were a better index of fetal well-being than longer-term measures. The application of the system to fetal monitoring is illustrated.

Criteria for the design of fetal heart rate analysis systems.

Criteria are described for the automated analysis of fetal pulse intervals, fetal movements and of uterine contractions measured externally, antenatally and interactively on-line, for implementation on a personal computer interfaced to an appropriate fetal monitor, and tested on 10,000 records. Measurements of short and longer term fetal heart rate variation are compared; both are required to identify sinister records. Recall and display of records acquired on the same patient over several weeks has proved a useful diagnostic aid.