Behavioral states in the human fetus during labor

Physiological control of fetal heart rate variability during labour: Implications and controversies

The interpretation of fetal heart rate (FHR) patterns is the only available method to continuously monitor fetal wellbeing during labour. One of the most important yet contentious aspects of the FHR pattern is changes in FHR variability (FHRV). Some clinical studies suggest that loss of FHRV during labour is a sign of fetal compromise so this is reflected in practice guidelines. Surprisingly, there is little systematic evidence to support this observation. In this review we methodically dissect the potential pathways controlling FHRV during labour-like hypoxaemia. Before labour, FHRV is controlled by the combined activity of the parasympathetic and sympathetic nervous systems, in part regulated by a complex interplay between fetal sleep state and behaviour. By contrast, preclinical studies using multiple autonomic blockades have now shown that sympathetic neural control of FHRV was potently suppressed between periods of labour-like hypoxaemia, and thus, that the parasympathetic system is the sole neural regulator of FHRV once FHR decelerations are present during labour. We further discuss the pattern of changes in FHRV during progressive fetal compromise and highlight potential biochemical, behavioural and clinical factors that may regulate parasympathetic-mediated FHRV during labour. Further studies are needed to investigate the regulators of parasympathetic activity to better understand the dynamic changes in FHRV and their true utility during labour. This article is protected by copyright. All rights reserved.

Simultaneous monitoring of maternal and fetal heart rate variability during labor in relation with fetal gender

Male gender is considered a risk factor for several adverse perinatal outcomes. Fetal gender effect on fetal heart rate (FHR) has been subject of several studies with contradictory results. The importance of maternal heart rate (MHR) monitoring during labor has also been investigated, but less is known about the effect of fetal gender on MHR. The aim of this study is to simultaneously assess maternal and FHR variability during labor in relation with fetal gender. Simultaneous MHR and FHR recordings were obtained from 44 singleton term pregnancies during the last 2 hr of labor (H_1, H₂ ). Heart rate tracings were analyzed using linear (time- and frequency-domain) and nonlinear indices. Both linear and nonlinear components were considered in assessing FHR and MHR interaction, including cross-sample entropy (cross-SampEn). Mothers carrying male fetuses (n = 22) had significantly higher values for linear indices related with MHR average and variability and sympatho-vagal balance, while the opposite occurred in the high-frequency component and most nonlinear indices. Significant differences in FHR were only observed in H₁ with higher entropy values in female fetuses. Assessing the differences between FHR and MHR, statistically significant differences were obtained in most nonlinear indices between genders. A significantly higher cross-SampEn was observed in mothers carrying female fetuses (n = 22), denoting lower synchrony or similarity between MHR and FHR. The variability of MHR and the synchrony/similarity between MHR and FHR vary with respect to fetal gender during labor. These findings suggest that fetal gender needs to be taken into account when simultaneously monitoring MHR and FHR.

Power spectrum analysis of fetal heart rate variability at near term and post term gestation during active sleep and quiet sleep

BACKGROUND

Spectral analysis of fetal heart rate variability is promising for assessing fetal condition. Before using spectral analysis for fetal monitoring it has to be determined whether there should be a correction for gestational age or behavioural state.

AIMS

Compare spectral values of heart rate variability between near term and post term fetuses during active and quiet sleep.

STUDY DESIGN

Case-control. Cases had a gestational age of > or =42 weeks; controls were 36 to 37 weeks. Fetuses were matched for birth weight percentile.

SUBJECTS

STAN registrations from healthy fetuses. For each fetus one 5-minute segment was selected during active and one during quiet sleep.

OUTCOME MEASURES

Absolute and normalized low (0.04-0.15 Hz) and high frequency power (0.4-1.5 Hz) of heart rate variability.

RESULTS

Twenty fetuses were included. No significant differences were found between cases and controls in absolute (481 and 429 respectively, P=0.88) or normalized low (0.78 and 0.80 respectively, P=0.50) or absolute (41 and 21 respectively, P=0.23) or normalized high frequency power (0.08 and 0.07 respectively, P=0.20) during active state. During rest, normalized low frequency power was lower (0.58 and 0.69 respectively, P=0.03) and absolute (16 and 10 respectively, P=0.04) and normalized high frequency power were higher (0.21 and 0.14 respectively, P=0.01) in cases compared to controls. Absolute and normalized low frequency power were higher during active state compared to rest in both groups (all P values <0.05).

CONCLUSIONS

We found sympathetic predominance during active state in fetuses around term. Post term parasympathetic modulation during rest was increased compared to near term.

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.

Foetal heart rate power spectrum response to uterine contraction

Cardiotocography is the most diffused prenatal diagnostic technique in clinical routine. The simultaneous recording of foetal heart rate (FHR) and uterine contractions (UC) provides useful information about foetal well-being during pregnancy and labour. However, foetal electronic monitoring interpretation still lacks reproducibility and objectivity. New methods of interpretation and new parameters can further support physicians' decisions. Besides common time-domain analysis, study of the variability of FHR can potentially reveal autonomic nervous system activity of the foetus. In particular, it is clinically relevant to investigate foetal reactions to UC to diagnose foetal distress early. Uterine contraction being a strong stimulus for the foetus and its autonomic nervous system, it is worth exploring the FHR variability response. This study aims to analyse modifications of the power spectrum of FHR variability corresponding to UC. Cardiotocographic signal tracts corresponding to 127 UC relative to 30 healthy foetuses were analysed. Results mainly show a general, statistically significant (t test, p<0.01) power increase of the FHR variability in the LF 0.03-0.2 Hz and HF 0.2-1 in correspondence of the contraction with respect to a reference tract set before contraction onset. Time evolution of the power within these bands was computed by means of time-varying spectral estimation to concisely show the FHR response along a uterine contraction. A synchronised grand average of these responses was also computed to verify repeatability, using the contraction apex as time reference. Such modifications of the foetal HRV that follow a contraction can be a sign of ANS reaction and, therefore, additional, objective information about foetal reactivity during labour.

Real-time spectral analysis of the fetal EEG: a new approach to monitoring sleep states and fetal condition during labor

Adverse perinatal events affecting cerebral functions are a major cause of neonatal mortality, morbidity, and long-term neurologic deficit. Intrapartum fetal EEG, which records fetal brain electrical activity, provides a monitoring modality for evaluating the fetal CNS during labor. In this study, we describe a new approach to such monitoring that is based on real-time spectral analysis of the fetal EEG during labor. Fourteen pregnant women with uncomplicated term pregnancies who went into labor participated in the study. Two suction-cup electrodes were applied to the fetal scalp at the occipitoparietal or parietal region after rupture of membranes. Real-time spectral analysis was used to determine the frequency and amplitude of the fetal EEG signal. The spectral edge frequency (SEF) was calculated as the frequency below which 90% of the power in the power spectrum resides. The average EEG amplitude and the SEF were displayed using the density spectral array technique. Fetal heart rate and intrauterine pressure were also measured. Two fundamental EEG patterns were identified: high-voltage slow activity and low-voltage fast activity. The SEF was found to be an excellent index of cyclic EEG activity. Fetal heart rate demonstrated increased variability and an elevated baseline during low-voltage fast activity, whereas both parameters decreased during high-voltage slow activity. During episodes of variable decelerations in the fetal heart rate, a decrease in the SEF was observed, accompanied by an increased EEG voltage. The results obtained substantiate the presence of sleep cycles in the human fetus. This kind of cortical activity monitoring may enable rapid alertness to cerebral hypoxia and allow for prompt intervention, thereby decreasing the risk for birth asphyxia and subsequent brain damage.

The effect of uterine contractions on intrapartum fetal heart rate analyzed by a computerized system

OBJECTIVE

Our goal was to assess the effect of uterine activity on fetal heart rate indexes during the active phase of labor with a computerized fetal heart rate monitoring system.

STUDY DESIGN

Twenty-six healthy women were studied in active labor without analgesia. Fetal heart rate was analyzed by a computerized system (Sonicaid, System 8000), providing a numeric analysis of the fetal heart rate indexes. Montevideo and Alexandria units were used for quantitative assessment of contractions.

RESULTS

A significant correlation was found between Montevideo units and short-term variation (r = -0.62, p < 0.001), episodes of high (r = -0.48, p < 0.01) and low (r = 0.58, p < 0.01) fetal heart rate variation, and frequency of large accelerations (r = -0.49, p < 0.01). A significant correlation was also found between Alexandria units and short-term variation (r = -0.645, p < 0.001), episodes of high fetal heart rate variation (r = -0.58, p < 0.01), and frequency of large accelerations (r = -0.49, p < 0.01).

CONCLUSIONS

In active labor fetal heart rate variability is significantly affected by the intensity and duration of contractions.

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

Parturition and fetal adaptation

The fetus as "patient" during labor and birth has become an increasingly important concept during the past 20 years. However, what is understood about fetal status during labor and how the fetus prepares for its approaching separation from its mother? Current information indicates that not only is the term fetus well prepared for the adaptation to extrauterine life, but this transition is facilitated by normal labor.

The effect of vibro-acoustic stimulation on fetal behavioral state organization

During the third trimester of pregnancy there is a gradual development of fetal behavioral states. These states are distinct and discontinuous modes of neural activity; they reflect a certain degree of maturity and/or integrity of the fetal brain and are homologous with those seen in newborn infants. Abnormal state development has been found in growth retarded fetuses and in fetuses of women with type-1 diabetes. Behavioral state organization is not easily influenced by external factors and most stimuli fail to induce a state change when the fetus is in quiet sleep (state 1F). However, fetuses do react to vibro-acoustic stimulation (VAS) with an electronic artificial larynx. This stimulus induces excessive fetal movements, prolonged tachycardia, disorganization of behavioral states, and state transitions normally not seen in healthy fetuses. The backgrounds for these excessive and unusual reactions are largely unknown. For the time being, it seems better not to use this device in clinical practice. In this review paper, data on the development of behavioral states and on fetal reactions to VAS are discussed.

Fetal movement during labor

The prognostic significance of antepartum fetal movement is well known; therefore it may be a variable in intrapartum fetal well-being. We report the simultaneous observation of fetal movement with fetal heart rate and uterine contractions by processed Doppler actograph signals during spontaneous labor of 22 normal women with normal fetal outcome. The mean percent incidence of fetal movement during labor was 17.3%. The percentage occurring during uterine contractions was 65.9%. Of all uterine contractions, 89.8% were associated with fetal movement. The proportion of time the fetus spent moving during uterine contractions (21.4%) was higher than between uterine contractions (12.9%). Uterine contractions associated with fetal movement were significantly longer than those not associated with fetal movement (p less than 0.0001). Mean percent incidence of fetal movement did not differ significantly between latent and active-phase labor. This study demonstrates a clear relationship between fetal movement and uterine contractions in labor.

Fetal heart rhythms during behavioural state 1F

Behavioural state 1F (quiet sleep) of the term fetus is defined on the basis of absence of eye and body movements, and the presence of a specific heart rate pattern (FHRP A), characterized by a stable heart rate with a small oscillation bandwidth. In the present paper the fetal heart rate pattern was studied in 39 enclosed periods with absence of fetal eye and body movements. In 37 periods the heart rate pattern met the criteria of FHRP A. Within FHRP A various distinct types of heart rhythm could be distinguished related to presence of breathing or regular mouthing and complete absence of movements. The bandwidth in the various heart rhythms differed significantly and was largest during breathing movements. During regular mouthing an oscillatory pattern was present with a frequency similar to the frequency of the clusters of mouthing movements. In 2 periods the heart rate deviated from the definition for FHRP A, i.e. a sinusoidal-like rhythm associated with sucking movements. These observations demonstrate the strong association between the fetal heart rate pattern and fetal movements during behavioural state 1F.

Intrapartum vibratory acoustic stimulation of the human fetus during episodes of decreased heart rate variability

The effects of intrapartum vibratory acoustic stimulation during periods of decreased fetal heart rate variability were studied in 25 healthy term fetuses. Fetal monitoring and real-time ultrasound scanning were used simultaneously to detect fetal response. Vibratory acoustic stimulation was provided by an artificial larynx generating a signal at 85 dB and 85 Hz. This stimulus was applied for 5 seconds on the maternal abdomen over the fetal head after a 20-minute period of decreased fetal heart rate variability. All fetuses reacted with an immediate fetal heart rate acceleration of at least 10 bpm (range: 10 to 35 bpm, mean +/- SD = 18.4 +/- 7.0), and 19 fetuses also had sudden fetal body movement. A deceleration of the fetal heart rate after the initial acceleration was observed in nine fetuses (range: 15 to 70 bpm, mean +/- SD = 45.5 +/- 16.5). The implications of these findings are discussed in relation to the possible use of fetal vibratory acoustic stimulation for intrapartum surveillance.

Maternal perception of fetal movements: the optimal duration of a recording period

A regular count of perceived fetal movements by the mother has been proposed as a screening method for the early recognition of fetal distress. Absence or a strongly decreased number of fetal movements during a particular period is considered as a sign of fetal distress. In the study presented, the optimal duration of a recording period for the maternal perception of fetal movements was examined. 186 pregnant patients at gestational ages of 32 and 38 weeks were asked to mark each perceived fetal movement on a time axis for two continuous hours. From these patients an 'optimal' group of 143 pregnancies was selected to constitute the study group. A window technique was applied to the 2 h recordings, searching for periods in which 0, 1 or 2 fetal movements were noted. 23% of the recordings at 32 weeks and 14% at 38 weeks showed absence of fetal movements for at least 30 min. At both 32 weeks and 38 weeks there was absence of fetal movements for more than 1 h in only 1.5% of the recordings. The findings are in agreement with the fetal behavioural state concept. A recording time of 1 h exceeds the normal duration of a fetal quiet-sleep state and minimizes the risk of unjustified suspicion of fetal distress.

The relationship between uterine contractions, fetal movements and fetal heart rate patterns in the active phase of labor

The relationship between fetal movements, fetal heart rate and uterine contractions was studied with a computerized system in 18 parturients during the active phase of labor. 80% of FHR accelerations and 39% of uterine contractions were associated with fetal trunk movements. The probability of association was greater in longer movements and larger accelerations. 98% of fetal movements which lasted 10-15 s, 98% of accelerations with an amplitude of 25-30 bpm and 96.4% of accelerations with a duration of 40-50 s were associated with fetal trunk movements.