Characterization of the reduced heart rate variation in growth-retarded fetuses

Summary. Fetal heart rate (FHR) variation has been studied by computerized numerical analysis in 20 growth-retarded fetuses and 20 normal fetuses matched for gestational age. FHR variation was significantly reduced in the 14 growth-retarded fetuses where there was clinical evidence of associated pathology. Rest - activity cycles were assessed by changes in FHR variation and fetal movements. The growth-retarded fetuses with reduced FHR variation showed the same pattern of rest and activity as normal fetuses but the changes in FHR variation were of lower amplitude. This was observed even in the subgroup of six fetuses with the lowest FHR variation. Thus the unreactive FHR patterns associated with growth retardation do not arise because the fetus spends less time in activity.     

Changes of pulsatility index from fetal vessels preceding the onset of late decelerations in growth-retarded fetuses.

Thirty-six growth-retarded fetuses selected from a population of 214 cases were studied by Doppler ultrasonography at weekly intervals for at least 4 weeks between the diagnosis of Doppler abnormalities suggestive of the existence of the brain-sparing effect (ie, ratio between umbilical artery and middle cerebral artery pulsatility indexes [PIs] above the 95th percentile of our reference limits) to the onset of antepartum late fetal heart rate (FHR) decelerations. Recordings were made from the umbilical artery, descending aorta, renal artery, internal carotid artery, and middle cerebral artery and the PIs were calculated. Statistically significant changes in PI occurred in all the vessels studied. However, different trends were found when the modifications in cerebral vessels were compared with those in fetal peripheral vascular beds and in the umbilical artery. In cerebral arteries, a nadir of vasodilatation was reached 2 weeks before the onset of antepartum late FHR decelerations, whereas significant changes in the peripheral and umbilical vessels occurred close to the onset of abnormal FHR patterns. This study demonstrates that despite a brain-sparing effect, there are further Doppler-detectable modifications in fetal circulation that differ between the cerebral and peripheral vascular beds.     

The value of the short-term fetal heart rate variation for timing the delivery of growth-retarded fetuses

Objective  To assess the clinical value of the short-term fetal heart rate variation (STV) for timing the delivery of severely growth-retarded fetuses, many associated with pre-eclampsia.
Design  Retrospective cohort study.
Setting  John Radcliffe Maternity Hospital, Oxford, UK.
Population  Two hundred and fifty-seven fetuses with a birthweight less than third percentile and a last computerised cardiotocography performed within 24 h of delivery.
Methods  Analysis of the relationship between antepartum STV and the perinatal outcome.
Main outcome measures  Stillbirth rate and the acid–base status at birth.
Results  There were no stillbirths or neonatal deaths (NNDs) within 24 h in the study population. Decreasing STV was correlated with earlier deliveries ( P < 0.001), lower birthweight ( P < 0.001), lower umbilical artery pH at birth ( P < 0.001), worse acid–base status at birth ( P < 0.001) and worse postnatal outcome ( P < 0.002). The STV was able to predict the presence or absence of acidaemia and metabolic acidaemia (area under the receiver operating characteristic curve 0.70 and 0.75, respectively, P < 0.001). The risk of metabolic acidaemia increased as the antepartum STV decreased, the optimum cutoff level being ≤ 3.0 milliseconds (positive and negative predictive values 64.6 and 86.6%). An STV ≤ 3.0 milliseconds was associated with markedly higher rate of metabolic acidaemia and early NNDs compared with an STV > 3.0 milliseconds (54.2 versus 10.5% and 8.3 versus 0.5%, respectively; P < 0.001). The deaths of the former group were all due to extreme prematurity and very low birthweight.
Conclusions  The antepartum STV is an important marker of perinatal outcome in severely growth-retarded fetuses. Timing the delivery of the most preterm and small fetuses remains a difficult task.     

Quantification of the fetal heart rate variability by spectral analysis in growth-retarded fetuses

The analysis of short-term variability of fetal heart rate in the frequency domain was performed. The fetal activity states (quiescence, trunk rotation, body movements, fetal breathing movements) were taken into account. The differences between the shapes of power spectra in physiological and growth-retarded fetuses were discussed.     

Effects of hypoxemic events on breathing, body movements, and heart rate variation: a study in growth-retarded human fetuses

In 14 growth-retarded human fetuses, breathing and body movements were studied before, during, and after late heart rate decelerations. Heart rate variation was measured before and after the decelerations. Breathing and body movements were significantly reduced during and after the deceleration. Heart rate variation was reduced after the decelerative episode. Since late heart rate decelerations are presumably signs of acute fetal hypoxemia, there is evidence that these reductions are caused by hypoxemia. The results suggest, furthermore, that just as in fetal sheep, these changes might be mediated by a change in brain activity state.     

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.     

Prognostic significance of single decelerations occurring in the antenatal CTG

Within systematic fetal supervision by CTG of the risk pregnancies sometimes single decelerations of variable type are observed. Most they didn't repeat. In the majority of the cases in follow up pregnancy the child will be born spontaneously without complications. In a lot of other cases, however, there appears fetal distress. For prognostic statistical evaluation of antenatal decelerations we watched prospectively the following groups: 1.43 cases with severe antenatal variable decelerations, 2.39 cases with mild antenatal variable decelerations, 3.88 cases without antenatal decelerations. - The appearance of severe decelerations was followed by fetal distress in 42%, by perinatal death in 12%, and by caesarean delivery in 40%. Fetal prognosis in this group is significantly more unfavourable than in the two other groups with mild decelerations (fetal distress 15%, caesarean section 23%, no fetal loss) or without decelerations (fetal distress 13%, caesarean section 10%, no fetal loss). - Single severe decelerations in antenatal CTG must be evaluated as a symptom of high fetal risk.     

The significance of fetal heart rate decelerations during nonstress testing

Over a 9-month time span, eight gravid women at high risk had fetal heart rate decelerations on nonstress tests (NSTs). This form of antepartum evaluation, the standard at our institution, was performed 918 times on 476 women during this period. Decelerations were required to be between 1 and 10 minutes in duration and less than 90 bpm, or greater than 40 bpm below baseline, for inclusion. Of the eight women (1.7% of the total tested), four had reactive and four nonreactive NSTs. All eight had contraction stress tests (CSTs) that were negative by definition. Of four women allowed to labor, two (50%) required cesarean section for fetal distress. Two instances of fetal death (25%) occurred during observation periods of 36 and 48 hours. Two infants were growth retarded, and two had abnormal cord positions. NSTs showing decelerations of this type, regardless of reactivity or of follow-up CST, are abnormal and should be viewed with alarm. In term pregnancy, such fetuses should be delivered. In preterm pregnancy with nonreactive NSTs, decelerations may also be valid grounds for delivery. Some discrimination is possible in preterm pregnancies when the NST is reactive.     

Short-term variation in abnormal antenatal fetal heart rate records

In a retrospective study the relation of reduced fetal heart rate variation to fetal acidemia was analyzed with a computerized system for numeric analysis. Between 1983 and 1987, 78 pregnancies were identified in which at least one record of the fetal heart rate had very low long-term variation. The outcome was analyzed to determine the numeric criteria of fetal heart rate variation that most efficiently detect a fetus that will die (preterminal) or is dying (terminal). Because fetal compromise was found on occasion to be associated with a slow sinusoidal fetal heart rate rhythm that increased measures of long-term variation. It was necessary to define a new index of short-term fetal heart rate variation (the 1/16 minute epoch-epoch variation). This was closely related to long-term variation (r = 0.9) but provided better detection of preterminal records as judged by metabolic acidemia at delivery or intrauterine death.     

短变异在胎心率监护中的应用

目的：采用计算机分析系统对胎心率图形中短变异和人工判读标准中长变异的各分型间的关系进行比较，并探讨短变异预测围生儿预后的价值：方法：分析了2001年12月至2002年9月3010份胎心率图型中，长变异各型相对应的短变异数值，及不同的短变异组围生儿不良预后的发生率。结果：短变异与长变异的各型之间呈正相关，短变异小于4．0ms组的围生儿预后不良的发生率显著高于短变异大于5．0ms组(P=0．039)。结论：计算机分析的短变异是反映胎心率基线变异的一个重要参数，对预测围生儿预后有重要价值，     

Fetal heart rate tracing during sickle cell crisis: a cause for transient late decelerations

A case of maternal sickle cell anemia crisis is presented. A continuous fetal heart rate (FHR) tracing demonstrates late decelerations that reversed when the mother's condition improved. The importance of recognizing this reversible late deceleration problem is discussed in terms of increasing fetal maturity.     

Computerised evaluation of fetal heart rate in post-term fetuses: long term variation

Computerised fetal heart rate records were obtained between 1987 and 1993 using the Sonicaid System 8000 for a cross-sectional study of postdates fetal heart rate variation; 567 singleton pregnancies at 41 and 43 weeks provided 1502 records. In all cases gestational age had been verified by ultrasound examination in early pregnancy. The mean minute range of the long term pulse interval variation, which is known to be correlated with fetal oxygenation was found to decrease progressively from an average value of 48.5 ms at 41 weeks to 46.4 ms and 42.4 ms at 42 and 43 or more weeks, respectively. When conservative management of postdate pregnancies is chosen, accurate measurements are needed to follow the evolution of fetal condition. Reference values for calculated pulse interval variation at later gestational ages are now provided.     

Clinical significance of fetal heart rate patterns during labor. II. Late decelerations.

Among a population of high-risk patients in labor who had continuous "direct" electronic monitoring, 147 presented late decelerations and 598 had no decelerations at the time the first stage was completed, or a cesarean section decided upon. A variety of clinical aspects of mother and fetus were analyzed, considering some alterations observed in the FHR pattern. Apgar scores were lower among decelerations, and there was a negative correlation between these two. Maternal pathology, other than PRM, was higher among decelerations and these required enhancement more often. There was very high association with tachycardia, saltatory, and fixed baseline among decelerations, and these infants were very often distressed and born depressed. Within the group of decelerations, small fetuses had lower Apgar scores. There was a negative correlation between number of decelerations and Apgar score. The small fetuses had a high incidence of tachycardia and fixed baseline, saltatory being almost absent. Their neonatal outcome was poor. A comparison of fetal response to distress was done considering age of gestation (premature, term, and postmature) and found to be different. The mechanisms involved in late deceleration are discussed, reviewing the published experimental work. When interpreting FHR patterns, age of gestation should be one of the most important considerations.     

Mechanisms of late decelerations in the fetal heart rate. A study with autonomic blocking agents in fetal lambs.

Fetal heart rate decelerations resembling the late deceleration FHR pattern were produced in fetal sheep by periodic occlusion of the maternal common hypogastric artery for 30-60 sec. Transient fetal hypertension also occurred during the occlusions. Alpha-adrenergic blockade with phentolamine eliminated or markedly reduced the hypertensive response. FHR decelerations still occurred intermittently with some occlusions; however, their character was greatly altered. After parasympathetic blockade with atropine, the decelerations were replaced by periodic FHR accelerations during the occlusions. These accelerations were, in turn, eliminated by the beta-adrenergic blocking agent, propranolol. In the presence of combined parasympathetic, alpha- and beta-adrenergic blockade, the FHR remained essentially constant during the hypogastric artery occlusions in non-acidemic fetuses. FHR decelerations persisted after parasympathetic or total autonomic blockade when the fetuses were significantly hypoxic, as judged by depressed arterial blood pH and base excess values. Beat-to-beat variability of the baseline FHR persisted in the face of severe hypoxia and acidosis. These observations demonstrate that reflex mechanisms are involved importantly in the genesis of late deceleration FHR patterns in the acutely hypoxemic fetus, but that direct depression of myocardial rhythmicity becomes a factor as hypoxic acidosis develops.     

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.     

Fetal heart rate decelerations following the administration of meperidine-promethazine during labor

A deceleration response lasting up to 7 min was observed in 53 fetuses (out of 1910 studied) following the administration of 75 mg meperidine and 25 mg promethazine intravenously to the mothers during labor. Thirty-six of these fetuses reacted with baseline tachycardia following the deceleration with or without loss of baseline variability. Seven fetuses showed a variable deceleration pattern and six fetuses reacted with a late deceleration pattern following the first deceleration. Two newborns from the group showing a late deceleration patten were delivered with an apgar score below 7 in 5 min. The probable mechanisms and significance of these changes are discussed.     

Labor and fetal heart rate decelerations: relation to fetal metabolic acidosis

Although intrauterine fetal compromise during labor accounts for a small proportion of cerebral palsy cases, fetal hypoxic-ischemic encephalopathy remains an important and sometimes preventable etiology. This paper reviews the mechanisms regulating fetal heart rate responses, pathogenesis of fetal metabolic acidosis, and thresholds for metabolic acidosis associated with hypoxic-ischemic encephalopathy. The knowledge of normal changes in fetal metabolic acidosis during labor together with changes in association with fetal heart rate decelerations, can aid in the interpretation and management of fetal heart rate tracings.     

An unusual cause and treatment of decelerations in fetal heart rate.

Decelerations of severe degree were detected during the monitoring of fetal heart rate at term. Decelerations continued despite the usual maneuvers in patient's position. Examination by ultrasound revealed that a loop of umbilical cord was held and squeezed in the fetal fist. The oxytocin infusion stimulated strong and frequent fetal movements which caused the fetal grip on umbilical cord to release and FHR decelerations to disappear. Induced labor progressed rapidly and within 5 h a healthy term infant was delivered.