Longitudinal assessment of behavioural transitions in healthy human fetuses during the third trimester of pregnancy

Electrocortical activity in the near-term ovine fetus: automated analysis using amplitude frequency components

We have designed an automated method for analyzing electrocortical (ECoG) activity in the near-term ovine fetus to process and quantitatively classify large amounts of data rapidly and objectively. Seven chronically catheterized fetal sheep were studied for 8h each at ~0.9 of gestation with continuous recording of ECoG activity using a computerized data acquisition system. Multiple ECoG amplitude and frequency parameters were scored from which we established animal specific parameter cut-off values as well as population based duration cut-off values to distinguish low-voltage/high frequency (LV/HF) and high-voltage/low frequency (HV/LF) state epochs, and indeterminate voltage/frequency (IV/F) and transition period activities. We have shown that the incidence of the predominant LV/HF and HV/LF activity states at 45% and 36% of the time, respectively, is comparable to that previously reported using semi-quantitative techniques with visual analysis. However, the duration of these state epochs is considerably shorter due to the detection of brief periods of IV/F activity which would be difficult to capture using visual analysis. Importantly, our findings in the healthy ovine fetus near-term using this automated ECoG scoring methodology now provide a framework from which to study maturational events in younger animals, and under adverse pregnancy conditions.

Twins' temperament: early prenatal sonographic assessment and postnatal correlation

OBJECTIVE

To study inter-twin differences in activity during early pregnancy and to examine their relationship to subsequent infant twins' temperament.

STUDY DESIGN

Measures of fetal motor activity (frequency, duration and number of movements) were collected from 26 twin pairs during ultrasound nuchal translucency scan at late first trimester and early second trimester (11 to 14 weeks gestation). In twenty-two patients, the twins were dizygotic (dichorionic); of them, 13 twin pairs were of different sexes, five were both females and four were both males. Of the four monozygotic twin pregnancies, two were dichorionic and two were monochorionic, three were both females.The more active fetus in each pair was noted according to the position and/or sex without reporting to parents. Reported maternal perception of the more active twin was documented at the mid-trimester anatomical scan. Maternally reported postnatal temperament data of the infants were collected at 3 and 6 months, using Rothbarts' Infant Behavior Questionnaire (IBQ).

RESULTS

After birth, maternal reports on infants' temperament and the more active twin in each pair were in good correlation with prenatal inter-twin differences in activity. The receiver operating characteristic (ROC) curves shows a better performance of ultrasound compared with maternal perception in prediction of the more active twin.

CONCLUSIONS

The features of fetal neurobehavioral activity provide the basis for individual differences in twins' activity in infancy. Differences in activity in early pregnancy even before the emergence of fetal behavioral patterns were followed by temperamental differences postnatally.

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.

Fetal behavior

Fetal behavior reflects the activity of the fetal central nervous system (CNS). Insight in fetal behavior is crucial for the understanding of normal fetal well-being and in the evaluation of the possibly compromised fetus. In order to recognize 'behavioral' patterns, linkage of variables (absence of movements, absence of eye movements, heart rate patterns) is obligatory. No single test can predict with certainty if the fetus is compromised and/or what the optimal timing is for the delivery. That is why the study of fetal behavior is very time-consuming. Development of more appropriate methods to analyze fetal behavior should have high priority in clinical perinatology.

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.

The relationship between the response to external light stimulation and behavioral states in the human fetus: how it differs from vibroacoustic stimulation

OBJECTIVE

To determine the effects of external light stimulation on fetal behavioral states and know the difference from those of vibroacoustic stimulation.

METHODS

A flashlight and a vibroacoustic stimulator was applied directly on the maternal abdomen to determine the response of 56 normal fetuses at 36-40 weeks gestation. Fetal heart rate (FHR) and body movements were recorded using an actocardiograph, and fetal eye movements were observed using real-time ultrasonography. Using Nijhuis's criteria, the fetal behavioral states (1F-4F) were determined. FHR acceleration was considered a fetal response to the stimulations.

RESULTS

The lag time between stimulation and fetal response was within 4 s. A positive response rate to the light stimulation was higher at behavioral states 2F (82%) and 3F (83%) than at state 1F (4%). Light stimulation changed the behavioral state of two of the six 3F fetuses (33%) from 3F to 4F. No change of state was observed in fetuses that were in states 1F and 2F. For vibroacoustic stimulation, fetal response was 100% positive and changes of states were observed frequently irrespective of the behavioral state before the stimulation.

CONCLUSION

Fetal response to light stimulation is closely connected to fetal behavioral states and may reflect some distinct stages of the sleep-wakefulness cycle.

Dynamic changes in the middle cerebral artery perfusion in normal full-term human fetuses in relation to the timing of behavioral state

Our aim is to evaluate serial changes in normal full-term fetal cerebral circulation according to the behavioral states. Flow velocity waveforms in the middle cerebral artery and fetal heart rate (FHR) were well recorded in ten of 19 cases by pulsed Doppler ultrasonography and actocardiography over 45 min, respectively. Behavioral states were classified as resting or active phase by FHR patterns. Resistance indices (RIs) were calculated every 5 s as an average of two consecutive waveforms, and median RI was chosen in each 2-min segment. In order to evaluate changes in median RI from active-to-resting transition to resting-to-active one statistically, differences in RI between two 2-min segments were examined using Mann-Whitney U-test. As a result, median RI was decreased to the minimum one in the active-to-resting transition for 12 min in all cases: significant decrease to the 2-min segment with the minimum one (P<0.01). Various types of increase to the maximum median RI during resting phase followed the minimum one: significant increase from the 2-min segment with the minimum one to that with the maximum one in all cases (P<0.001 in eight cases, P<0.01 in two cases). Thereafter, median RI was decreased from the end of resting phase in the resting-to-active transition for 12 min in all cases: significant decrease from the last 2-min segment of resting phase in all cases (P<0.01). We reveal that fetal cerebral circulation changes dynamically in relation to the timing in each behavioral state.

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.

Computerised analysis of unstimulated and stimulated behaviour in fetuses with intrauterine growth restriction

Unstimulated (passive) and stimulated behaviour, in the form of fetal heart rate (FHR) and activity (FA)) was studied in 32 normal fetuses and 14 fetuses with intrauterine growth restriction (IUGR). FHR and FA were recorded using a single 1.5 MHz ultrasound transducer and analysed by computer. A 5 s vibroacoustic stimulus (VAS) (electronic artificial larynx) was used for the stimulation studies. The IUGR fetuses had significantly different patterns of both unstimulated and stimulated behaviour compared to normally grown fetuses. When unstimulated they had lower FA rates than the normally grown fetuses but this was only statistically significant at 28-31 weeks. They also spent a significantly lower proportion of time exhibiting high FHR variation at 28-31 weeks. Following VAS the IUGR fetuses had lower FA responses at all gestations and lower FHR responses from 32 weeks, though only the differences in FA response at 28-31 weeks were statistically significant. Of the 14 fetuses with IUGR, all but one exhibited passive behaviour (ERR and/or FA) that was outside the 10-90th range, for normally grown fetuses, whilst 6 of the 14 had responses to VAS that were within the normal range. We do not feel that computerised assessment of stimulated behaviour in preterm IUGR fetuses confers any advantage over passive observations.

State transitions in uncomplicated pregnancies after term

A behavioural state transition is the time interval between two different behavioural states. In low-risk fetuses, the fetal heart rate pattern (FHRP) is the first variable to change in transitions from 1F to 2F ('non-REM-sleep' to 'REM-sleep') and the last variable to change in transitions from 2F to 1F. This is not the case in IUGR (intra-uterine growth retardation), and absence of a specific order in which behavioural variables are changing might be an indication for a (mild) disturbance of the fetal central nervous system (CNS). We investigated whether state transitions in twelve low risk term fetuses (39-41 weeks post menstrual age, PMA; control group) differ from those in twelve uncomplicated pregnancies > 41 weeks PMA (study group). All subjects underwent one behavioural study in which fetal heart rate pattern, eye and body movements were recorded simultaneously. We recorded 23 transitions from 1F to 2F and 20 from 2F to 1F. Median (range) duration for transitions from 1F to 2F was 85 (10-180) s in the study group, and 60 (10-180) s in the control group. Transitions from 2F to 1F lasted 80 (10-140) and 60 (30-100) s, respectively. In both groups, the FHRP was the first variable to change in transitions from 1F to 2F, however, in transitions from 2F to 1F, no specific order in change of variables could be demonstrated. We conclude that the study of transitions does not distinguish between the term and after term fetuses under optimal conditions. Whether or not the analysis of state transitions can be used to distinguish 'normal' from 'abnormal' fetuses and detect the fetus at risk after term awaits further study.

Computerised analysis of behaviour in normal and growth-retarded fetuses

Fetal behaviour [fetal heart rate (FHR) variation and movements (FA)] was studied in 27 normally grown fetuses and in 18 fetuses with intrauterine growth restriction (IUGR). FHR and FA were recorded using a single 1.5 MHz ultrasound transducer and analyzed by computer. The IUGR fetuses had significantly lower FA rates than the normally grown fetuses at all gestation times. They also spent a significantly lower proportion of time exhibiting high FHR variation at 28-31 weeks. Only two of the eighteen IUGR fetuses had abnormal biophysical profile scores (BPS) at the time of recording and yet all but one of them had either FHR or FA patterns that were outside the 10-90th centile range for the normally grown fetuses, suggesting that FHR and FA abnormalities predated BPS changes. More of the IUGR fetuses had abnormalities of FA than FHR. Finally, within the IUGR fetuses, those with small head circumferences (less than 3rd centile) had lower FA rates during periods of both low and high FHR variation, though this was only statistically significant for periods of low FHR variation (P < 0.05). This preliminary study offers the possibility that such objective evaluation of fetal behaviour could be used in a clinical setting and provide a more sensitive method of fetal assessment than the BPS.

Fetal behaviour in normal and compromised fetuses. An overview

Fetal intrauterine behaviour is not a stable situation but a continuous alternation of states characterized by significant changes in fetal motility, heart rate, hemodynamics, metabolism and response to stimulation. Associations between fetal heart rate patterns and movements occur from 26-28 weeks of gestation onwards. As fetuses grow older these variables become gradually more related temporally and clustered in behavioural states similar to those present in newborns. This article describes the technique of recording and analyzing fetal behaviour, its development in normal pregnancy and its influence on different physiological parameters that are assessed in clinical practice. Furthermore the deviations from the norm occurring in compromised fetuses are described.

Fetal behaviour and the sudden infant death syndrome (SIDS)

To examine whether differences in sleep maturation could be identified before birth, behavioural studies were carried out in 28 fetuses. Studies were possible in all 28 fetuses at 28 weeks, but only in 26 fetuses at 36 weeks (two fetuses delivered before 36 weeks). The risk of sudden infant death syndrome (SIDS) was determined using the Oxford SIDS scoring system. The fetuses at greater risk of SIDS had coincidence of behavioural characteristics for a significantly lower percentage of the time than those at low risk. This difference reached significance (p < or = 0.05) only at 36 weeks.