Coincidence of behavioural state parameters in the human fetus at three gestational ages

Non-linear Methods Predominant in Fetal Heart Rate Analysis: A Systematic Review

The analysis of fetal heart rate variability has served as a scientific and diagnostic tool to quantify cardiac activity fluctuations, being good indicators of fetal well-being. Many mathematical analyses were proposed to evaluate fetal heart rate variability. We focused on non-linear analysis based on concepts of chaos, fractality, and complexity: entropies, compression, fractal analysis, and wavelets. These methods have been successfully applied in the signal processing phase and increase knowledge about cardiovascular dynamics in healthy and pathological fetuses. This review summarizes those methods and investigates how non-linear measures are related to each paper's research objectives. Of the 388 articles obtained in the PubMed/Medline database and of the 421 articles in the Web of Science database, 270 articles were included in the review after all exclusion criteria were applied. While approximate entropy is the most used method in classification papers, in signal processing, the most used non-linear method was Daubechies wavelets. The top five primary research objectives covered by the selected papers were detection of signal processing, hypoxia, maturation or gestational age, intrauterine growth restriction, and fetal distress. This review shows that non-linear indices can be used to assess numerous prenatal conditions. However, they are not yet applied in clinical practice due to some critical concerns. Some studies show that the combination of several linear and non-linear indices would be ideal for improving the analysis of the fetus's well-being. Future studies should narrow the research question so a meta-analysis could be performed, probing the indices' performance.

Developmental trajectories of general and breathing movements in fetal twins

This study examined the developmental trajectories of general and breathing movements in fetal twins. Fetal movement patterns were assessed from real-time ultrasound recordings performed at 12-15, 20-23, and 28-32 weeks of gestation in 42 twin pairs. Results indicated that both general movements and breathing movements followed a curvilinear, inverted U-shaped curve. Developmental trajectories were unrelated within pairs of twins and were not associated with gestational age at birth and birth weight. However, sex differences were found for general movements with males displaying more time making general movements at 21 weeks and a steeper decline in time spent making general movements during the second half of pregnancy than females. These age-related changes in fetal movements may reflect CNS development. These findings also suggest that twins' behavioral development is largely independent of co-twin development, gestational age at birth, and birth weight, but not of fetal sex.

Maternal exercise, season and sex modify the daily fetal heart rate rhythm

AIM

The knowledge on biological rhythms is rapidly expanding. We aimed to define the longitudinal development of the daily (24-hour) fetal heart rate rhythm in an unrestricted, out-of-hospital setting and to examine the effects of maternal physical activity, season and fetal sex.

METHODS

We recruited 48 women with low-risk singleton pregnancies. Using a portable monitor for continuous fetal electrocardiography, fetal heart rate recordings were obtained around gestational weeks 24, 28, 32 and 36. Daily rhythms in fetal heart rate and fetal heart rate variation were detected by cosinor analysis; developmental trends were calculated by population-mean cosinor and multilevel analysis.

RESULTS

For the fetal heart rate and fetal heart rate variation, a significant daily rhythm was present in 122/123 (99.2%) and 116/121 (95.9%) of the individual recordings respectively. The rhythms were best described by combining cosine waves with periods of 24 and 8 hours. With increasing gestational age, the magnitude of the fetal heart rate rhythm increased, and the peak of the fetal heart rate variation rhythm shifted from a mean of 14:25 (24 weeks) to 20:52 (36 weeks). With advancing gestation, the rhythm-adjusted mean value of the fetal heart rate decreased linearly in females (P < .001) and nonlinearly in males (quadratic function, P = .001). At 32 and 36 weeks, interindividual rhythm diversity was found in male fetuses during higher maternal physical activity and during the summer season.

CONCLUSION

The dynamic development of the daily fetal heart rate rhythm during the second half of pregnancy is modified by fetal sex, maternal physical activity and season.

Linear and nonlinear features of fetal heart rate on the assessment of fetal development in the course of pregnancy and the impact of fetal gender

OBJECTIVE

This work aims to investigate the impact of gestational age and fetal gender on fetal heart rate (FHR) tracings.

APPROACH

Different linear and nonlinear parameters indicating correlation or complexity were used to study the influence of fetal age and gender on FHR tracings. The signals were recorded from 99 normal pregnant women in a singleton pregnancy at gestational ages from 28 to 40 weeks, before the onset of labor. There were 56 female fetuses and 43 male.

MAIN RESULTS

Analysis of FHR shows that the means as well as measures of irregularity of FHR, such as approximate entropy and algorithmic complexity, decrease as gestation progresses. There were also indications that mutual information and multiscale entropy were lower in male fetuses in early pregnancy.

SIGNIFICANCE

Fetal age and gender seem to influence FHR tracings. Taking this into consideration would improve the interpretation of FHR monitoring.

STUDIES IN FETAL BEHAVIOR: REVISITED, RENEWED, AND REIMAGINED

Among the earliest volumes of this monograph series was a report by Lester Sontag and colleagues, of the esteemed Fels Institute, on the heart rate of the human fetus as an expression of the developing nervous system. Here, some 75 years later, we commemorate this work and provide historical and contemporary context on knowledge regarding fetal development, as well as results from our own research. These are based on synchronized monitoring of maternal and fetal parameters assessed between 24 and 36 weeks gestation on 740 maternal-fetal pairs compiled from eight separate longitudinal studies, which commenced in the early 1990s. Data include maternal heart rate, respiratory sinus arrhythmia, and electrodrmal activity and fetal heartrate, motor activity, and their integration. Hierarchical linear modeling of developmental trajectories reveals that the fetus develops in predictable ways consistent with advancing parasympathetic regulation. Findings also include:within-fetus stability (i.e., preservation of rank ordering over time) for heart rate, motor, and coupling measures; a transitional period of decelerating development near 30 weeks gestation; sex differences in fetal heart rate measures but not in most fetal motor activity measures; modest correspondence in fetal neurodevelopment among siblings as compared to unrelated fetuses; and deviations from normative fetal development in fetuses affected by intrauterine growth restriction and other conditions. Maternal parameters also change during this period of gestation and there is evidence that fetal sex and individual variation in fetal neurobehavior influence maternal physio-logical processes and the local intrauterine context. Results are discussed within the framework of neuromaturation, the emergence of individual differences, and the bidirectional nature of the maternal-fetal relationship.We pose a number of open questions for future research. Although the human fetus remains just out of reach, new technologies portend an era of accelerated discovery of the earliest period of development

Linear and nonlinear analysis of heart rate patterns associated with fetal behavioral states in the antepartum period

BACKGROUND

Fetal behavioral states are important indicators of fetal physiology and pathology associated to typical fetal heart rate (FHR) patterns.

AIM

To provide linear and nonlinear analysis of FHR patterns associated with fetal behavioral states regarding a better understanding of these states and patterns.

STUDY DESIGN AND SUBJECTS

Fifty FHR tracings from normal term pregnancies with a median duration of 40.3 min were acquired with the SisPorto 2.01 system for computerized analysis of cardiotocograms. Each tracing was divided into consecutive 10-minute segments and each segment was classified by two experts as pattern A, B, C or D.

OUTCOME MEASURES

Linear and nonlinear indices were computed in each segment, namely mean FHR, long-term irregularity index (LTI), very low (VLF), low (LF) and high (HF) frequency spectral indices, approximate entropy (ApEn) and sample entropy (SampEn). Kappa statistic (kappa) and proportions of agreement (Pa) were used for assessment of inter-observer agreement. Bootstrap percentile confidence intervals and nonparametric statistical tests were calculated for statistical inference.

RESULTS

Overall agreement between experts in pattern classification was good to excellent with values for kappa and Pa of 0.74 (95% CI: 0.64-0.94) and 0.94 (95% CI: 0.92-0.96), respectively. Most linear domain indices increased significantly with rising fetal activity whereas the opposite occurred with nonlinear indices, except for SampEn(2, 0.1). LF/(MF+HF) ratio also significantly increased with fetal activity, denoting an increased sympatho-vagal balance.

CONCLUSIONS

Results support the hypothesis that entropy and linear variability indices measure different FHR features. FHR patterns associated with active sleep (B) and active wakefulness (D) evidenced more signs of autonomous nervous system activity, with sympatho-vagal imbalance, and less signs related to complexity or irregularity control systems than patterns associated with calm sleep (A) and calm wakefulness (C).

Sleep-wake states and their regulatory mechanisms throughout early human development

The emergence of sleep states is one of the most significant aspects of development. Descriptions of both neonatal and late fetal behavior and studies on the organization of sleep have shown that fetus and newborns exhibit spontaneously discrete and cyclic patterns of active sleep (AS) and quiet sleep (QS). Human fetuses and neonates sleep most of their life, and AS is the prevailing state even during the first postnatal months. Several hypotheses to explain central nervous system development consider that AS is the expression of a basic activation program for the central nervous system that increases the functional competence of neurons, circuits, and complex patterns before the organism is called on to use them. Current results indicate the maturation of QS not only coincides with the formation of thalamocortical and intracortical patterns of innervation and periods of heightened synaptogenesis, since this sleep state is also associated with important processes in synaptic remodeling. In fact, several studies suggest that the information acquired during wakefulness is further processed during AS and QS. This article reviews the processes involved in the timing of both AS/QS and sleep/wake alternating patterns throughout early human development. A growing body of evidence indicates that the duration of unmodulated parental care and noncircadian environmental conditions may be detrimental for the establishment of these basic rhythmicities. As a consequence, alterations in parental/environmental entraining factors may well contribute to disturb sleep and feeding commonly experienced by preterm infants. Further knowledge on the early establishment of sleep-wake states regulatory mechanisms is needed to improve modalities for appropriate stimulation in the developing human being.

Human fetal and neonatal movement patterns: Gender differences and fetal-to-neonatal continuity

Longitudinal quantification of leg movements per minute for human subjects during both fetal and neonatal periods was accomplished from videotapings conducted antenatally (ultrasonography 30, 34, and 37 weeks gestational age) and postnatally (birth and 6 weeks of age). Fetal/neonatal subjects displayed decreasing numbers of leg movements per minute during antenatal development (30 to 37 weeks), followed by increasing numbers of leg movements per minute during postnatal development (birth to 6 weeks of age). Male subjects displayed greater numbers of leg movements per minute than female subjects during both antenatal and postnatal development. Fetal-to-neonatal continuity for numbers of leg movements per minute was found for comparisons between fetal (37 weeks gestational age) and neonatal (during sleep states at birth) measures, and females displayed a stronger and different movement continuity pattern than males. These results indicate a differential time course for neurobehavioral development of male and female fetuses/neonates, and the findings have implications for the clinical assessment of fetal neurobehavioral development and well-being.

Spontaneous motor activity in the perinatal infant before and after birth: stability in individual differences

This study was undertaken to determine if a relationship existed between the duration of spontaneous general movements before and after birth. Twenty-two infants were examined three times as fetuses between 38 and 40 weeks gestational age and three times as neonates between 2 and 4 weeks postnatal age. Motor activity level during active sleep periods was quantified by direct sonographic visualization for fetuses and by videotaped images of trunk movement for neonates. We found that both fetuses and neonates exhibited stable individual differences in motor activity level. In addition, infants who moved at a certain rate as fetuses generally moved at the same relative rate as neonates up to 4-weeks postnatal age. Our findings suggested that individual differences in motor activity level in the 1st month following birth probably arise during fetal life.

Temporal organization of fetal behavior from 24-weeks gestation onwards in normal and complicated pregnancies

Developmental aspects of behavioral organization were investigated in 29 healthy fetuses from 24-weeks gestation onwards: (a) short-term association between body (GM) and eye (EM) movements; (b) linkage of pairs of the three state variables [fetal heart rate pattern (FHRP), GM, and EM]; and (c) sequence of change of state variables during transitions. Linkage and sequence were also studied in complicated pregnancies. Short-term association between GM and EM was well established after 28 weeks. Linkage of state variables improved considerably after 32-34 weeks. FHRP was the first variable to change during synchronized transitions from 1F to 2F between 28-39 weeks, and the last variable during 2F to 1F transitions between 32-39 weeks. Although clear developmental patterns could be recognized, the interfetal variability was such that identification of the abnormal fetus is still difficult. Only transitions were significantly different in growth-restricted fetuses, as they showed no specific sequence of change. Assessing the temporal organization of fetal behavior seems, therefore, until now, not of great clinical value.

Developments in CTG analysis

FHR monitoring has been the subject of many debates. The technique, in itself, can be considered to be accurate and reliable both in the antenatal period, when using the Doppler signal in combination with autocorrelation techniques, and during the intrapartum period, in particular when the FHR signal can be obtained from a fetal ECG electrode placed on the presenting part. The major problems with FHR monitoring relate to the reading and interpretation of the CTG tracings. Since the FHR pattern is primarily an expression of the activity of the control by the central and peripheral nervous system over cardiovascular haemodynamics, it is possibly too indirect a signal. In other specialities such as neonatology, anaesthesiology and cardiology, monitoring and graphic display of heart rate patterns have not gained wide acceptance among clinicians. Digitized archiving, numerical analysis and even more advanced techniques, as described in this chapter, have primarily found a place in obstetrics. This can be easily explained, since the obstetrician is fully dependent on indirectly collected information regarding the fetal condition, such as (a) movements experienced by the mother, observed with ultrasound or recorded with kinetocardiotocography (Schmidt, 1994), (b) perfusion of various vessels, as assessed by Doppler velocimetry, (c) the amount of amniotic fluid or (d) changes reflected in the condition of the mother, such as the development of gestation-induced hypertension and (e) the easily, continuously obtainable FHR signal. It is of particular comfort to the obstetrician that a normal FHR tracing reliably predicts the birth of the infant in a good condition, which makes cardiotocography so attractive for widespread application. However, in the intrapartum period, many traces cannot fulfil the criteria of normality, especially in the second stage. In this respect, cardiotocography remains primarily a screening and not so much a diagnostic method. As long as continuous monitoring of fetal acid-base balance has not been extensively tested in clinical practice, microblood sampling of the fetal presenting part (Saling, 1994) is a useful adjunct. The problem with non-normal tracings is that their significance is very often unclear. They may indicate serious fetal distress, finally resulting in preventable destruction of critical areas in the fetal brain and damage to various organs; or, on the contrary, they may indicate temporary changes in cardiovascular control as a reaction to the intermittent effects on fetal haemodynamics of, for example, uterine contractions, whether or not in combination with partial or complete compression of umbilical cord vessels or the vessels on the chorionic plate (van Geijn, 1994). Many factors influence the FHR and its variability, which further complicates the interpretation of FHR patterns; some have been discussed here in some detail. Undoubtedly, there is a need for quantitative and objective FHR analysis, as long as it does not lead to erroneous results. Close collaboration between engineers and clinicians is a prerequisite for further advances in this field. Decision support systems certainly have a future but only if they are able to take into account a large set of clinical data and can combine it with data obtained from FHR signals and other parameters referring to the fetal condition, such as fetal growth, Doppler velocimetry, amniotic fluid volume and biochemical and biophysical data obtained from the mother. Basic technical concepts inherent in computerized CTG analysis, such as sampling rate (Chang et al, 1995), signal loss, artefact detection (van Geijn et al, 1980), further processing of intervals, archiving in digitized format and monitor display, should receive considerable attention. There is still a long way to go until decision support systems find their way into obstetric practice. Further developments can only be achieved thanks to efforts of many basic and clinical researchers, wo

Morphology of active sleep--quiet sleep transitions in normal human term fetuses

Periods of no coincidence (PsNC) among state variables appear to be more predictive of neurobehavioral outcome than the amount of time spent in any particular behavioral state. It has recently been suggested that analysis of the ordering of state variables during a state transition may provide results equivalent to full state analysis. If this were the case, then there ought to be a relationship between the duration of PsNC and fetal heart rate (FHR)-fetal eye movement (FEM) sequencing at the time of a state change. To test this hypothesis, we compared full state analysis with analysis of individual state transitions for 52 normal human fetuses between 38 and 42 weeks of gestation. For the study population as a whole, FHR was the first variable to change in 62 (77%) of 81 1F-->2F transitions and FEM was the first variable to change in 50 (63%) of 79 2F-->1F transitions (chi 2 = 67.9, p < 0.001). Ordering of FHR and FEM at the time of a state change was reversed in 8 (67%) of 12 fetuses with PsNC > or = 15% and is only 6 (15%) of 40 fetuses with PsNC < 15% (chi 2 = 12.5, p < 0.001). We conclude that fetuses who exhibit poor state organization more often display a FHR-FEM sequence at the time of a state transition which is opposite that of fetuses with considerably better state control. However, since only one-third of fetuses with reversed FHR-FEM sequencing actually exhibited more than one such episode, it is unlikely that isolated analysis of state transitions will provide a reliable measure of behavioral state organization in the individual fetus.

Fetal heart rate patterns and chronic exposure to antiepileptic drugs

Fetal heart rate (FHR) characteristics of fetuses exposed and not exposed to antiepileptic drugs (AEDs) were studied. FHR is considered to reflect central nervous system (CNS) integrity. Three intervals during pregnancy were investigated: 20, 32, and 38 weeks. At 32 and 38 weeks, FHR was studied in relation to quiet (C1F) and active (C2F) sleep periods. For each tracing, a baseline was determined and accelerations and decelerations were identified. To assess FHR variability, the long-term irregularity, interval difference and absolute beat-to-beat indexes, and the bandwidth were calculated for 30-s intervals between accelerations and decelerations. No marked differences were noted between study and control groups concerning basal FHR and the occurrence of accelerations. For FHR derived from the fetal ECG, all indexes of FHR variability and the bandwidth were lower for the study group as compared with the control group, although the differences did not reach statistical significance. Our study shows that chronic prenatal exposure to AEDs does not seriously interfere with modulation of fetal heart rhythm by the CNS.

Fetal motility and chronic exposure to antiepileptic drugs

The potential influence of antiepileptic drugs (AEDs) on fetal CNS function was studied with respect to motility patterns. Quantitative and qualitative aspects of spontaneous fetal activity were investigated for chronic AED-exposed fetuses and controls at three intervals during pregnancy: i.e. 20, 32 and 38 weeks. Movements were observed applying real-time ultrasound. Third trimester rest-activity cycles were determined according to the fetal behavioural state concept. Quantitative analysis revealed no marked differences in gross fetal motility between AED-exposed fetuses and controls. Both groups demonstrated the same developmental trend from midterm towards the third trimester. The number of trunk movements decreased, while their median duration increased. The incidence of fetal eye movements during C2F was lower for AED-exposed fetuses than for controls (significant for 38 weeks). In qualitative analysis, general movements of AED-exposed fetuses were more often labeled as suspect or abnormal than those of control fetuses (respectively, 8 out of 31 and 1 out of 20; P = 0.06). Future studies concerning chronic fetal AED-exposure and fetal CNS function should focus on qualitative rather than quantitative aspects of motility.

Quantitated fetal heart rhythm at 20, 32 and 38 weeks of gestation and dependence on rest-activity patterns

Quantitative parameters of fetal heart rate (FHR) were automatically analysed at 20, 32 and 38 weeks of pregnancy. FHR was obtained both by the fetal ECG method and by wide range Doppler ultrasound with autocorrelation. At 32 and 38 weeks, FHR was studied in relation to fetal rest-activity according to the fetal behavioural state concept (coincidence 1F and 2F). Basal fetal heart rate was significantly higher at 20 weeks of gestation than at 32 and 38 weeks. The number of accelerations increased significantly from 20 weeks to 32 and 38 weeks for C2F periods. Parameters of FHR variability, i.e. ID, ABB, LTI indices and bandwidth, were higher during periods C2F compared to periods C1F. Lowest values of all four parameters were found at 20 weeks gestation. The ID index, which is a measure of short-term variability increased significantly between 32 to 38 (C2F). The absolute values of ID, ABB and LTI were lower for ultrasound recordings than for the fetal ECG.

Influences on heart rate variability in spontaneously breathing preterm infants

To investigate the influence of maturational and physiological factors on heart rate variability in spontaneously breathing very preterm infants (n = 29) a multiparametric study was performed during the first 3 days of life in infants born at a gestational age below 33 weeks. Four times a day, RR-intervals, respiration curve and rate, transcutaneously measured blood gases and observed body movements were recorded while the infants were asleep. All data were stored simultaneously in a micro-computer. Non-invasively measured blood pressure and patency of the ductus arteriosus were documented as well. Four sets of short- (STV) and long term variability (LTV) indices were calculated. Both STV and LTV appeared to be significantly influenced by conceptional and postnatal age in the appropriate for gestational age infants. LTV was influenced by the behavioural state and body movements. During state coincidence 2 ('active sleep') LTV was influenced by respiratory rate and the variations in transcutaneous PO2. An effect of blood pressure or ductus patency could not be demonstrated.

Fetal rest-activity cycles and chronic exposure to antiepileptic drugs

Rest-activity patterns were studied in fetuses exposed to antiepileptic drugs (AEDs) and in control fetuses at three intervals during pregnancy: 20, 32, and 38 weeks. At 20 weeks, periods of rest and activity were distinguished on the basis of fetal motility. Trunk, head, and arm movements were totaled. Periods of absence of movements for greater than 3 min were found in 20 of 31 recordings from AED-exposed fetuses compared with 11 of 20 recordings from controls (p greater than 0.05). The duration of these periods of inactivity did not differ significantly between the two groups. At 32 and 38 weeks, information on fetal motility and fetal heart rate (FHR) were combined to recognize rest-activity patterns according to the fetal behavioral state concept. At 32 weeks, three true fetal behavioral states were found for the study group, while there were none in the control group. Coincidence 1F through 4F occurred significantly less frequently at 32 weeks than at 38 weeks, regardless of whether fetuses were AED-exposed or not: 59% vs. 82% for the study group and 59% vs. 80% for the controls. At 38 weeks, true fetal behavioral states appeared in 20 of 34 fetuses exposed to AEDs and in 17 of 35 controls (p greater than 0.05). The sequence in which parameters changed within state transitions was found to follow the same preferred pattern in both groups. For transitions from behavioral state 1F (quiet sleep) into 2F (active sleep) the FHR pattern changed significantly earlier than fetal body or eye movements, while for the reverse transitions the FHR pattern changed significantly later (p less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)