Similarities and Differences in Behavioral State Organization during Sleep Periods in the Perinatal Infant Before and After Birth

Association between neonatal phototherapy and sleep: The Japan Environment and Children's Study

This observational cohort study aimed to evaluate the association between the duration of neonatal phototherapy and sleep-and-wakefulness states at 1 month, 1.5 years, and 3 years of age. We analysed data from 77,876 infants using the Japan Environment and Children's Study, a nationwide birth cohort study. The participants were divided into three groups: no phototherapy, short phototherapy (1-24 h), and long phototherapy (>24 h). Multiple regression analysis was performed to assess the effect of phototherapy duration on infant sleep at each age after adjusting for potential risk factors. A longer duration of phototherapy was associated with a shorter sleep time over 24 h at 1 month of age (β, -0.62; SE, -0.77 to -0.47) when compared with a shorter duration of, or no, phototherapy, following the adjustment of confounding factors. Contrastingly, the short duration group, when compared with the no phototherapy group, was associated with later sleep onset (β, 0.04; SE, 0.00-0.08) and later sleep offset (β, 0.05; SE, 0.01-0.09) at 1.5 years of age. We concluded that the duration of phototherapy may be transiently associated with sleep duration in infants, as emphasised by the shortening of the total sleep time per 24 h at 1 month of age.

Factors affecting yawning frequencies in preterm neonates

Yawning is a long neglected behavioral pattern, but it has recently gained an increasing interdisciplinary attention for its theoretical implications as well as for its potential use as a clinical marker, with particular regard to perinatal neurobehavioral assessment. The present study investigated the factors affecting yawning frequencies in hospitalized preterm neonates (N = 58), in order to distinguish the effects of hunger and sleep-related modulations and to examine the possible impact of demographic and clinical variables on yawning frequencies. Results showed that preterm neonates yawned more often before than after feeding, and this modulation was not explained by the amount of time spent in quiet sleep in the two conditions. Moreover, second born twins, known to be more prone to neonatal mortality and morbidity, showed increased yawning rates compared to first born twins. Overall, our results are consistent with the hypothesis that yawning frequencies in preterm neonates are modulated by separate mechanisms, related e.g. to hunger, vigilance and stress. These findings, although preliminary and based only on behavioral data, might indicate that several distinct neuropharmacological pathways that have been found to be involved in yawn modulation in adults are already observable in preterm neonates.

Child maltreatment severity and sleep variability predict mother–infant RSA coregulation

Regulatory processes underlie mother-infant interactions and may be disrupted in adverse caregiving environments. Child maltreatment and sleep variability may reflect high-risk caregiving, but it is unknown whether they confer vulnerability for poorer mother–infant parasympathetic coordination. The aim of this study was to examine mother–infant coregulation of respiratory sinus arrhythmia (RSA) in relation to child maltreatment severity and night-to-night sleep variability in 47 low-income mother–infant dyads. Maternal and infant sleep was assessed with actigraphy and daily diaries for 7 nights followed by a mother–infant still-face procedure during which RSA was measured. Higher maltreatment severity was associated with weakened concordance in RSA coregulation related to the coupling of higher mother RSA with lower infant RSA, suggesting greater infant distress and lower maternal support. In addition, higher infant sleep variability was associated with infants’ lower mean RSA and concordance in lagged RSA coregulation such that lower maternal RSA predicted lower infant RSA across the still-face procedure, suggesting interrelated distress. The findings indicate that adverse caregiving environments differentially impact regulatory patterns in mother–infant dyads, which may inform modifiable health-risk behaviors as targets for future intervention.

Sleep-wake regulation in preterm and term infants

Study Objectives

In adults, wakefulness can be markedly prolonged at the expense of sleep, e.g. to stay vigilant in the presence of a stressor. These extra-long wake bouts result in a heavy-tailed distribution (highly right-skewed) of wake but not sleep durations. In infants, the relative importance of wakefulness and sleep are reversed, as sleep is necessary for brain maturation. Here, we tested whether these developmental pressures are associated with the unique regulation of sleep–wake states.

Methods

In 175 infants of 28–40 weeks postmenstrual age (PMA), we monitored sleep–wake states using electroencephalography and behavior. We constructed survival models of sleep–wake bout durations and the effect of PMA and other factors, including stress (salivary cortisol), and examined whether sleep is resilient to nociceptive perturbations (a clinically necessary heel lance).

Results

Wake durations followed a heavy-tailed distribution as in adults and lengthened with PMA and stress. However, differently from adults, active sleep durations also had a heavy-tailed distribution, and with PMA, these shortened and became vulnerable to nociception-associated awakenings.

Conclusions

Sleep bouts are differently regulated in infants, with especially long active sleep durations that could consolidate this state’s maturational functions. Curtailment of sleep by stress and nociception may be disadvantageous, especially for preterm infants given the limited value of wakefulness at this age. This could be addressed by environmental interventions in the future.

The rhythm of a preterm neonate's life: ultradian oscillations of heart rate, body temperature and sleep cycles

The objectives are to characterize oscillations of physiological functions such as heart rate and body temperature, as well as the sleep cycle from behavioral states in generally stable preterm neonates during the first 5 days of life. Heart rate, body temperature as well as behavioral states were collected during a daily 3-h observation interval in 65 preterm neonates within the first 5 days of life. Participants were born before 32 weeks of gestational age or had a birth weight below 1500 g; neonates with asphyxia, proven sepsis or malformation were excluded. In total 263 observation intervals were available. Heart rate and body temperature were analyzed with mathematical models in the context of non-linear mixed effects modeling, and the sleep cycles were characterized with signal processing methods. The average period length of an oscillation in this preterm neonate population was 159 min for heart rate, 290 min for body temperature, and the average sleep cycle duration was 19 min. Oscillation of physiological functions as well as sleep cycles can be characterized in very preterm neonates within the first few days of life. The observed parameters heart rate, body temperature and sleep are running in a seemingly uncorrelated pace at that stage of development. Knowledge about such oscillations may help to guide nursing and medical care in these neonates as they do not yet follow a circadian rhythm.

Behavioral-state development and sleep-state differentiation during early ontogenesis

Sleep is a key process in neurodevelopment and essential for the maturation of fundamental brain functions. Premature birth can disturb the initial steps of sleep maturation, which may contribute to the impairment of neurodevelopment. It is thus fundamental to understand the maturation of the various sleep states and the quality of cerebral function in each vigilance state, as well as the development of sleep cyclicity, in at-risk neonatal infants, particularly those born premature. The objective of this review is to provide a precise description of sleep states and cycles and their rhythmic organization in premature and term newborns according to their gestational age. Technical aspects of polysomnography, which requires a high level of expertise in neonates, are also described. Principles of the visual interpretation of polysomnography, including the simultaneous analysis of behavioral (spontaneous motricity and eye movements), polysomnographic parameters (electro-oculogram, electrocardiogram, respiration), and electroencephalography patterns are presented. The neurophysiology of sleep ontogenesis and its interaction with brain maturation are discussed, highlighting the crucial role of sleep states and their duration in premature newborns. In particular, the involvement of myoclonic twitches in functional connectivity in sensorimotor development is discussed. Indeed, sleep quality, determined by combined polysomnographic parameters, reflects either normal or pathological developmental processes during the neonatal period. The fundamental place of neurophysiological explorations in the early detection of sleep disorders is discussed, as well as their potential consequences on neurodevelopmental care to improve the prevention of neurodevelopmental impairment.

Mother Schema, Obstetric Dilemma, and the Origin of Behavioral Modernity

What triggered the emergence of uniquely human behaviors (language, religion, music) some 100,000 years ago? A non-circular, speculative theory based on the mother-infant relationship is presented. Infant "cuteness" evokes the infant schema and motivates nurturing; the analogous mother schema (MS) is a multimodal representation of the carer from the fetal/infant perspective, motivating fearless trust. Prenatal MS organizes auditory, proprioceptive, and biochemical stimuli (voice, heartbeat, footsteps, digestion, body movements, biochemicals) that depend on maternal physical/emotional state. In human evolution, bipedalism and encephalization led to earlier births and more fragile infants. Cognitively more advanced infants survived by better communicating with and motivating (manipulating) mothers and carers. The ability to link arbitrary sound patterns to complex meanings improved (proto-language). Later in life, MS and associated emotions were triggered in ritual settings by repetitive sounds and movements (early song, chant, rhythm, dance), subdued light, dull auditory timbre, psychoactive substances, unusual tastes/smells and postures, and/or a feeling of enclosure. Operant conditioning can explain why such actions were repeated. Reflective consciousness emerged as infant-mother dyads playfully explored intentionality (theory of mind, agent detection) and carers predicted and prevented fatal infant accidents (mental time travel). The theory is consistent with cross-cultural commonalities in altered states (out-of-body, possessing, floating, fusing), spiritual beings (large, moving, powerful, emotional, wise, loving), and reports of strong musical experiences and divine encounters. Evidence is circumstantial and cumulative; falsification is problematic.

4D ultrasound study of fetal facial expressions in the third trimester of pregnancy

OBJECTIVE

To evaluate the frequencies of fetal facial expressions in the third trimester of pregnancy, when fetal brain maturation and development are progressing in normal healthy fetuses.

METHODS

Four-dimensional (4 D) ultrasound was used to examine the facial expressions of 111 healthy fetuses between 30 and 40 weeks of gestation. The frequencies of seven facial expressions (mouthing, yawning, smiling, tongue expulsion, scowling, sucking, and blinking) during 15-minute recordings were assessed. The fetuses were further divided into three gestational age groups (25 fetuses at 30-31 weeks, 43 at 32-35 weeks, and 43 at ≥36 weeks). Comparison of facial expressions among the three gestational age groups was performed to determine their changes with advancing gestation.

RESULTS

Mouthing was the most frequent facial expression at 30-40 weeks of gestation, followed by blinking. Both facial expressions were significantly more frequent than the other expressions (p < .05). The frequency of yawning decreased with the gestational age after 30 weeks of gestation (p = .031). Other facial expressions did not change between 30 and 40 weeks. The frequency of yawning at 30-31 weeks was significantly higher than that at 36-40 weeks (p < .05). There were no significant differences in the other facial expressions among the three gestational age groups.

CONCLUSIONS

Our results suggest that 4D ultrasound assessment of fetal facial expressions may be a useful modality for evaluating fetal brain maturation and development. The decreasing frequency of fetal yawning after 30 weeks of gestation may explain the emergence of distinct states of arousal.

Immediate effects of phototherapy on sleep in very preterm neonates: an observational study

Process C (internal clock) and Process S (sleep-wake homeostasis) are the basis of sleep-wake regulation. In the last trimester of pregnancy, foetal heart rate is synchronized with the maternal circadian rhythm. At birth, this interaction fails and an ultradian rhythm appears. Light exposure is a strong factor influencing the synchronization of sleep-wake processes. However, little is known about the effects of phototherapy on the sleep rhythm of premature babies. It was hypothesized that sleep in preterm infants would not differ during phototherapy, but that a maturation effect would be seen. Sleep states were studied in 38 infants born < 32 weeks gestational age and/or < 1 500 g birth weight. Videos of 3 h were taken over the first 5 days of life. Based on breathing and movement patterns, behavioural states were defined as: awake; active sleep; or quiet sleep. Videos with and without phototherapy were compared for amounts of quiet sleep and active states (awake + active sleep). No significant association between phototherapy and amount of quiet sleep was found (P = 0.083). Analysis of videos in infants not under phototherapy revealed an increase in time spent awake with increasing gestational age. The current data suggest that the ultradian rhythm of preterm infants seems to be independent of phototherapy, supporting the notion that sleep rhythm in this population is mainly driven by their internal clock.

Fetal Neurology: The Role of Fetal Stress

Fetal development and growth, as well as the timing of birth is influenced by the intrauterine environment. Many environmental factors causing the fetal stress can interfere with fetal development and leave long-term and profound consequences on health. Fetal glucocorticoid overexposure has primarily significant consequences for the development of the central nervous system. In response to an adverse intrauterine conditions, the fetus is able to adapt its physiology to promote survival. However, these adaptations can result in permanent changes in tissue and organ structure and function that directly ‘program’ predisposition to disease. Cardiometabolic disorders, behavioral alterations and neuropsychiatric impairments in adulthood and/ or childhood may have their roots in the fetal period of life. Fetal response to stress and its prenatal and lifelong consequences are discussed in this review.

How to cite this article

Kadić AS. Fetal Neurology: The Role of Fetal Stress. Donald School J Ultrasound Obstet Gynecol 2015;9(1):30-39.

Prenatal behavior of the C57BL/6J mouse: a promising model for human fetal movement during early to mid-gestation

The study of fetal neurobehavioral development in genetically altered mice promises a significant advance in our understanding of the prenatal origins of developmental disabilities in humans. Despite their importance, little is known about fetal neurobehavioral development in mice. In this study, we observed prenatal behavioral patterns of the C57BL/6J mouse, a common background strain for genetically altered mice, and report their similarity to those observed in the early to mid-gestation human fetus. Fetal offspring from pregnant C57BL/6J dams were observed on the day before birth (E18 of a 19-day gestation). Scoring and analysis of fetal movement included Prechtl's Method for Qualitative Assessment, Interlimb Movement Synchrony, a measure of the temporal relationship between movements of limb pairs, and Behavioral State, quantified through detailed analysis of high and low amplitude limb movements. With the exception of fetal breathing movements, all categories and patterns of behavior typically reported in the early to mid-gestation human fetus were observed in the C57BL/6J mouse fetus. Our results suggest that behavioral analysis of fetal C57BL/6J mice may yield important new insights into early to mid-gestation human behavioral development.

Behavioural state linkage in the ovine fetus near term

Nine fetal sheep were surgically prepared with placement of electrocortical and electro-ocular electrodes for monitoring behavioural state activity to determine the relationship of adjacent low-voltage (LV)/rapid eye movement (REM) and high-voltage (HV)/non-(N)REM epoch durations and the inter-epoch transition time. Animals were subsequently studied over an 8-hour period with behavioural state epoch duration and transition time assessed using paired t-test and regression analysis. For all animals, the duration of LV/REM epochs averaged 14.8+/-0.8 (SEM) minutes which was significantly greater than that for HV/NREM epochs at 10.1+/-0.5 min (P<0.01). The mean duration of LV/REM to HV/NREM transition periods at 93+/-3 s was also significantly longer than that for the HV/NREM to LV/REM transition periods at 78+/-6 s (P<0.05). HV/NREM epoch duration was positively correlated with the prior LV/REM epoch duration with a group mean correlation of 0.59 (P<0.01). HV/NREM epoch duration was likewise positively correlated with the subsequent LV/REM epoch duration with a group mean correlation of 0.46 (P<0.01). We conclude that the transition time into HV/NREM is longer than that into LV/REM for the ovine fetus near term which may involve differences in the rate of maturation of cycling control mechanisms for these two behavioural states and earlier development of REM-on versus REM-off pathways. The positive LV/REM-HV/NREM linkage relationships also support a homeostatic model of behavioural state control whereby LV/REM and HV/NREM timings are both controlled by accumulation of propensity for these states during the other state and favours an interactive process between these states in the brain's growth and development.

Normal fetal motility: an overview

After 35 years of real-time two-dimensional sonography, and now that 4D sonography is within our grasp, this article presents an overview of present-day knowledge of normal fetal motility. A literature search was carried out on articles from 1970, using the keywords: 'fetal', 'movements', 'motility', 'movement patterns', 'ultrasound' and 'sonography'. Inclusion criteria were human studies and use of real-time sonography. Articles were screened for type of motor assessment procedure, in terms of whether they: specified movements for participating body parts (specific movement pattern, SMP), were qualitative (performance in terms of speed and amplitude), were quantitative, identified behavioral states, stated the duration of observation, and specified gestational age. We noted developmental milestones obtained for each study aim. One of four aims was identified for each article, depending on whether it focused on emergence, development, or continuity after birth of the movement patterns, or on the relationship of various motor aspects to other parameters that evaluate fetal condition, such as blood flow and fetal heart rate. A total of 109 relevant articles was identified, examining 9862 fetuses. Assessment was performed primarily with analysis of SMPs (89%); 52% also included non-SMPs (NSMPs), 78% included quantification, 24% assessment of quality, and 32% behavioral states. The duration of observation was 1 h or longer in 50% of the studies. The focus in 28 studies was on emergence, in 44 it was on development, in five it was on continuity and in 32 it was on relationship of the movements with other parameters of fetal well-being. A few milestones identified were determination of the strictly age-related emergence of SMPs and behavioral states, the highly reproducible quality of SMPs throughout gestation, the age-related trends in quantified SMPs, the continuity in quality and quantity after birth, and the close relationship between motility and heart-rate variability, flow parameters, and behavioral states. Periods of longest inactivity recorded before 20 weeks were 13 min; after 30 weeks they were 45 min. Much insight was obtained into the development of motility and its relationship to other parameters from those articles applying comparable assessment procedures. An assessment procedure with well-defined SMPs, qualitative and quantitative aspects of SMPs and NSMPs, and an observation period dependent on age are advocated for future research.

Neurobehavioral assessment before birth

The complexities of neurobehavioral assessment of the fetus, which can be neither directly viewed nor manipulated, cannot be understated. Impetus to develop methods for measuring fetal neurobehavioral development has been provided by the recognition that individual differences in neurobehavioral functioning do not originate with birth and acceptance of the key contribution of the antenatal period to postnatal life. Research has centered around four aspects of fetal functioning: heart rate, motor activity, behavioral state, and responsivity to stimulation. Longitudinal studies have revealed that the developmental trajectories of these characteristics parallel the developing nervous system, detected a transitional period between 28 and 32 weeks gestation, and established within-fetal stability during the second half of gestation. Despite the promise of fetal stimulation and habituation paradigms as measures of neural functioning, significant safety and ethical concerns exist. Construction of a unified fetal neurobehavioral scale is premature until a sufficient degree of normative data is available and the predictive validity of specific aspects of fetal neurobehavior to child developmental outcomes is better established.

Ontogeny of sleep and awake states in relation to breathing in preterm infants

This review will focus on the development of behavioural states and breathing during early developmental stages prior to term gestation. Although these behavioural states are immature during early development, their cyclicity is clearly seen. Preterm infants characteristically have a large proportion of indeterminate sleep and small amount of wakefulness. Whereas oxygenation is relatively stable during active and quiet sleep in ventilated preterm infants, indeterminate sleep and arousals are associated with hypoxaemic episodes. Arousals have also been linked to apnoea in spontaneously breathing infants. Since well-defined sleep cycles are beneficial for the oxygenation of preterm infants, we should explore ways to promote their natural sleep while they are exposed to neonatal intensive care. Care practices such as clustering procedures, kangaroo care and optimal positioning have been shown to improve the integrity of sleep. Optimizing the sleep cycling might improve the long-term outcome of preterm infants. More studies in this area are clearly needed.

Development of fetal and neonatal sleep and circadian rhythms

The origin of sleep and circadian rhythms development is found during the fetal period. Both quiet (NREM) and active (REM) sleep are distinguishable during the last 10 weeks of gestation. Comparable to fetuses, low risk preterm infants recorded at 30-40 weeks postconceptional age, had a similar development of sleep i.e. an increase in quiet sleep and a decrease in indeterminate sleep. A further development in sleep organization characterized by increased slow wave and spindle activity during quiet sleep and coupling with circadian rhythm takes place during the first 6 months of life in both term and preterm infants.Circadian rhythm of fetal heart rate synchronized with maternal rest-activity, heart rate, cortisol, melatonin, and body temperature rhythms is present during the last 10 weeks of gestation. Although maternally influenced, circadian rhythm antenatally becomes ultradian at birth. Both preterm and term infants show a significant increase in circadian body temperature rhythm amplitude during the first 3 months of life.

Fetal state concordance predicts infant state regulation

Fetal state organization reflects the development of the central nervous system but may also portend individual differences in postnatal state organization. The goal of the present study was to determine the extent to which fetal state regulation, defined as the percentage of an observation period in which fetal heart rate and movement concordance was displayed, is associated with neonatal state regulation. Neonatal state regulation was evaluated through a standard neurobehavioral assessment at 2 weeks postpartum. Biobehavioral concordance was measured in 52 normally developing fetuses at 24, 30 and 36 weeks gestation using an actocardiograph; the neonatal assessment was administered to 41 of these as infants. Intrafetal stability in biobehavioral concordance did not emerge prior to 36 weeks. Fetuses with higher concordance at 36 weeks were infants that displayed better state regulation during the exam, including more alertness and orientation (r(35)=0.29), less cost of maintaining attention (r=0.36), less irritability (r=-0.41), better regulatory capacity (r=0.47), a greater range of available states (r=0.34), and were significantly more likely to maintain control during the most aversive portions of the exam F(1,31)=4.63, p<0.05). These results support fetal state as a stable individual attribute that is conserved across the prenatal and neonatal periods.

Sudden fetal and infant deaths: shared characteristics and distinctive features

Recent evidence suggests sudden infant death syndrome (SIDS) infants have a diminished capacity to respond to autonomic challenges during a vulnerable developmental period. We speculate that a dysfunction or altered trajectory in the development of the autonomic nervous system may be detected in utero and also may play a role in the pathogenesis of unexplained late stillbirth. Some fetuses, as well as infants, may be more vulnerable than others to autonomic challenges during periods of autonomic instability. Investigation of potential shared underlying mechanisms in both SIDS and unexplained stillbirth will require expanded epidemiological investigation of genetic and environmental correlates along with a systematic study of developmental physiology and neuropathology. As with SIDS, there are likely important interactions between genetic susceptibility and environmental exposures occurring during gestation, which lead to infants who have altered trajectories or deficits in autonomic function and who need to be identified before they enter the periods of greatest risk.

Fetal responsiveness to maternal passive swinging in low heart rate variability state: effects of stimulation direction and duration

Pregnant women, carrying end of gestation fetuses (38-41 weeks gestational age) were either gently rocked in an anterior posterior plane in a rocking chair or gently swayed laterally in a garden glider. Stimulation lasted for either 5 or 26 s (R5 & R26, SW5 & SW26). Fetal heart rate (HR) (bpm) and ultrasonically detected fetal movements were recorded 26 s before and during stimulation. Heart rate data were processed two ways: (a) ANOVAs performed on average values for each group and (b) comparisons of the proportion of subjects in each group showing HR accelerative change (AC), HR decelerative change (DC), or no change (NC) using chi2 statistics. HR direction and amplitude of changes were determined with the help of a conservative procedure previously developed and fitted to multidirectional HR responses (Lecanuet, Granier-Deferre, Jacquet, & Busnel, 1992). Results of ANOVAs indicated that a 26-s rocking stimulation induced a significant average HR acceleration (4.53 bpm) compared to a nonstimulated (control) group. Five seconds of rocking had a weaker, but still significant, effect on HR acceleration, but the two swaying conditions did not reliably affect either the HR or behavioral measures. Processing data nonparametrically confirmed that R26 stimulation evoked mostly AC (72%) and identified a gradual decrement of AC and DC percentage responses from Group R5, SW26 to Group SW5 while NC percentages raised. Hypotheses concerning the target sense activated by this stimulation were considered in relation to responses to auditory stimuli.

Antenatal origins of individual differences in heart rate

This study examines prenatal-to-postnatal stability in heart rate and variability from mid-gestation through the first year of life. Fetal heart rate data were collected from 52 healthy fetuses at 24, 30, and 36 weeks gestation, and again at 2 weeks and 12 months of age. Fetal heart rate measures were stable during gestation and positively associated with neonatal and infant measures. Maternal pulse rate and oxygen saturation were moderately associated with fetal heart rate. Together, fetal cardiac (heart rate and variability) and maternal physiologic measures (blood pressure and oxygen saturation) explained 40 and 48% of the variance in heart rate and variability, respectively, at 1 year of age. These common measures of individual differences in autonomic function are enduring characteristics that originate during fetal development.

Temporal pattern and spectral complexity as stimulus parameters for eliciting a cardiac orienting reflex in human fetuses

The purpose of this study was to determine whether temporal pattern and/or spectral complexity were important stimulus parameters for eliciting a cardiac orienting reflex (OR) in low-risk human fetuses. Each of 28 term fetuses was exposed to four sounds formed from the four different combinations of temporal pattern (pulsed, continuous) and spectral complexity (sine wave, /â/). The fetal cardiac electrical signal was captured transabdominally at a rate of 1024 Hz, and fetal R-waves were extracted by using adaptive signal-processing techniques. We found that pulsed sounds elicited a significantly greater decrease in heart rate (HR) than did continuous sounds. However, the HR response was relatively unaffected by spectral complexity. For the pure tone and the phoneme used in this study, our results indicate that temporal characteristics were more effective at eliciting a cardiac OR in human fetuses than was spectral complexity.

Human fetuses have nonlinear cardiac dynamics

Approximate entropy (ApEn) is a statistic that quantifies regularity in time series data, and this parameter has several features that make it attractive for analyzing physiological systems. In this study, ApEn was used to detect nonlinearities in the heart rate (HR) patterns of 12 low-risk human fetuses between 38 and 40 wk of gestation. The fetal cardiac electrical signal was sampled at a rate of 1,024 Hz by using Ag-AgCl electrodes positioned across the mother's abdomen, and fetal R waves were extracted by using adaptive signal processing techniques. To test for nonlinearity, ApEn for the original HR time series was compared with ApEn for three dynamic models: temporally uncorrelated noise, linearly correlated noise, and linearly correlated noise with nonlinear distortion. Each model had the same mean and SD in HR as the original time series, and one model also preserved the Fourier power spectrum. We estimated that noise accounted for 17.2-44.5% of the total between-fetus variance in ApEn. Nevertheless, ApEn for the original time series data still differed significantly from ApEn for the three dynamic models for both group comparisons and individual fetuses. We concluded that the HR time series, in low-risk human fetuses, could not be modeled as temporally uncorrelated noise, linearly correlated noise, or static filtering of linearly correlated noise.

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.

High vagal tone is associated with more efficient regulation of homeostasis in low-risk human fetuses

Homeostasis is maintained primarily by the parasympathetic nervous system and is thought to provide a physiological substrate for the development of complex behaviors. This investigation was undertaken to test the hypothesis that infants with high parasympathetic tone are more efficient regulators of homeostasis than infants with low parasympathetic tone. Respiratory sinus arrhythmia (RSA) was used as a measure of parasympathetic tone, and the efficiency of homeostatic control was quantified, for each infant, by the slope (SRSA) and correlation coefficient (RRSA) of the regression line relating fluctuations in heart period and fluctuations in RSA. To test our hypothesis, we examined the relationship between RSA and both SRSA and RRSA in 34 low-risk human fetuses between 36 and 40 weeks gestation. We found that fetuses who were parasympathetic-dominated had larger SRSA and RRSA values, and hence were more efficient regulators of homeostasis, than fetuses who were sympathetic-dominated. The results of our analyses are important because they establish, very early in development, a physiological basis for the relationship between vagal tone and the development of complex behaviors.

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.

Behavioral state affects heart rate response to low-intensity sound in human fetuses

The cardiac orienting reflex is elicited by a low-intensity sound, it consists of a sustained heart rate (HR) deceleration, and it is a specific physiological correlate of cognitive processing. In this study we examined the relationship between behavioral state and the cardiac orienting reflex in 75 human fetuses between 36 and 40 weeks gestation. Each fetus was stimulated with a 30-s speech sound at an average intensity of 83 dB SPL in quiet sleep (QS) and active sleep (AS). The fetal cardiac electrical signal was captured transabdominally at a rate of 1024 Hz and fetal R-waves were extracted using adaptive signal processing. Fetal behavioral states were assigned based on HR pattern and the presence or absence of eye and general body movements. We found that a significant HR deceleration occurred, in both QS and AS, following stimulus onset. However, HR decelerations occurred more often in QS than AS; and for fetuses exhibiting a HR deceleration, the magnitude of the deceleration was greater in AS compared to QS. In addition, in AS female fetuses exhibited a larger, more sustained HR deceleratory response than male fetuses, but the seconds x gender interaction in QS was not significant. Based on these results, we concluded that behavioral state is an important determinant of the HR deceleratory response in human fetuses.

Heart rate dynamics in low risk human fetuses

Evaluation of nonlinear heart rate (HR) dynamics has received considerable attention in the pediatric literature because such analyses not only provide insight into underlying control mechanisms, but may also help to differentiate between normal and abnormal infants. The purpose of this study was to determine, in eight low risk human fetuses, if nonlinear HR dynamics could be identified by analyzing the dispersion of interbeat intervals at slow (Ds) and fast (Df) HRs. The fetal cardiac electrical signal was captured transabdominally at a resolution of +/- 1 ms. To test the null hypothesis, that the time series is the result of a linear stochastic process, Ds and Df for the original time series were compared with the values calculated for three linear models. The linear models were constructed to preserve the major statistical properties of the original time series, including the mean, SD, and the Fourier power spectrum. For each fetus, there was no evidence of nonlinear cardiac dynamics based on analyses of Ds and Df. In contrast, the distribution of adjacent R-R intervals and the pattern of change across three successive interbeat intervals both revealed significant nonlinearities in HR control in each fetus. If the difference between normal and abnormal infants is the result of aberrant control of nonlinear processes, then our findings indicate that parameters which describe the nonlinearity may be more useful then Ds and Df in assigning a risk status.

Temporal stability in the distribution of behavioral states for individual human fetuses

Although behavioral state analyses have been useful in differentiating between groups of normal and at-risk fetuses, the large between-subject differences in the percent time spent in the various behavioral states poses a major obstacle in identifying abnormal neurological functioning in individual fetuses. Does this variability represent a true difference in state organization between fetuses, or does it simply reflect individual fluctuations in state control at the time of observation? To answer this question, we examined each of 33 human fetuses for 4 h on three separate days between 38 and 40 weeks gestation. The percent time spent in each behavioral state and in transition and insertion periods was determined for each of the three 4-h study sessions, and within-subject analysis of variance was performed to obtain an objective measure of state profile consistency for each fetus. We found that, on the average, fetuses exhibited remarkable within-subject consistency in their state profiles. However, even among this group of low-risk fetuses, there were significant differences in the degree of state organization achieved by individual fetuses. These findings, which indicate the existence of a well-developed central nervous system before birth, suggest that individual differences in the consistency of behavioral state profiles may be indexing important between-subject differences in neurological development.