Computerized assessment of fetal behavioral states

Automated analysis of antepartum fetal heart rate in relation to fetal rest-activity states: a longitudinal study of uncomplicated pregnancies using the Sonicaid System 8000

OBJECTIVES

To learn which fetal heart rate (FHR) parameters change with gestational age and to demonstrate the relation with fetal rest-activity states.

STUDY DESIGN

FHR and fetal movements were recorded in 12 uncomplicated pregnancies from 26 weeks gestational age onwards. Seventy-two FHR recordings of 60 min duration were analysed by a computer (Sonicaid System 8000). Statistical analysis of complete 60 min recordings and selective periods of rest and activity comprised Spearman's rank correlation test, regression analysis and Wilcoxon's signed-rank test.

RESULTS

The time needed to meet the system's criteria of normality decreased with gestational age. The incidence of accelerations (ACC), overall FHR variation (VAR) and variation during 'episodes of high variation' (VEHV) increased with gestational age in the total population, but statistical significance of these relations could only be demonstrated in a minority of individual fetuses. Most FHR parameters differed significantly for periods of fetal rest and activity. No FHR parameters showed a relation with gestational age during periods of rest.

CONCLUSIONS

The increase of ACC, VAR and VEHV with gestational age is primarily due to an increase during fetal activity. The considerable variation within and between fetuses, however, can only be partly explained by fetal rest-activity states.

Categorization of heart rate-eye movement patterns in human fetuses using the statistical technique of discriminant analysis

The purpose of this study was to determine if discriminant analysis could be used to categorize fetal heart rate (FHR) - fetal eye movement (FEM) patterns. Statistical characteristics from 27 normal human fetuses at term for behavioral states, transitions, and insertions were established by combining the digitized FHR-FEM data for subjectively identical epochs. The mean FHR, the variance about the mean, and the presence or absence of FEM were calculated for each 3-min block in a sliding moving window with a 1-min step size. For each fetus, discriminant analysis was then used to assign 3-min blocks to either a behavioral state, a transition, or an insertion by comparing the statistical properties of a 3-min block with that of the data base. We found no difference between discriminant analysis and visual assignment in the average time spent in behavioral states 1F, 2F, and 4F, or in the mean duration of the transition/insertion periods. There was a highly significant linear relationship between computer-generated and visually-determined durations for behavioral states 1F (r = 0.972, p < 0.0001) and 2F (r = 0.989, p < 0.0001) and for the transition/insertion periods (r = 0.863, p < 0.0001). We conclude that discriminant analysis is a reliable computer-based method for behavioral state identification.

The relationship between heart rate and eye movement in the human fetus at 38-40 weeks of gestation

The purpose of this study was to compare two different methods for assessing fetal heart rate (FHR)--fetal eye movement (FEM) synchronization: (1) periods of high (HV) and low (LV) variability in the FHR and the presence (EM) and absence (NEM) of FEM were determined by visual inspection and the degree of association between FHR and FEM was assessed in terms of the fraction of study time for which no periods of LV-NEM and HV-EM could be identified; and (2) the maximum cross-correlation coefficient (rmax) and the lag at rmax (Lmax) were determined by direct computer analysis of FHR and FEM data for each fetus. Twenty normal human fetuses between 38 and 40 weeks of gestation were examined for a total of 2051 min (mean 103 min, range 72-150 min). In general, the state HV-EM was observed approximately twice as often as was the state LV-NEM; neither of these two states could be identified during 12.4% of the study time. The coefficient rmax was calculated assuming a sliding 3-min moving window, using either the average FHR (mean 0.53, range 0.31-0.85) or the variability in the FHR (mean 0.52, range 0.18-0.77). No relationship was found between rmax and Lmax calculated using the mean FHR and the fraction of time for which no state could be identified (P = 0.995). When the cross-correlation analysis was performed using FHR variability, a statistically significant relationship was found between the periods of no coincidence (of states LV-NEM and HV-EM) and rmax and Lmax (r2 = 0.32; P = 0.04).(ABSTRACT TRUNCATED AT 250 WORDS)

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.

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)

Automated analysis of near-term antepartum fetal heart rate in relation to fetal behavioral states: the Sonicaid System 8000

Fetal heart rate and fetal movements were recorded in 16 uncomplicated near-term pregnancies. The recordings were used to evaluate a system for automated fetal heart rate analysis (Sonicaid System 8000). Fetal rest-activity patterns were considered in the analysis. The mean duration of C2F periods "active sleep," 33 minutes) was significantly greater than that of C1F periods ("quiet sleep," 19 minutes) (p less than 0.001). The incidence of accelerations and decelerations and the overall fetal heart rate variations were greater during C2F than during C1F (p less than 0.001). In 11 of 16 C1F periods, the system classified the fetal heart rate variation as "questionable" or "abnormal." Episodes of high variation were identified in only 3 of 16 C1F periods, but they were found in all 18 C2F periods. Episodes of low variation were identified in 14 of the 16 C1F periods but were not found in any C2F periods. During C2F periods, the system's criteria of normality were met in all cases but one; they were not met during any of the C1F periods. Thus the diagnosis of fetal distress should not be based merely on the absence of accelerations, low fetal heart rate variation, or absence of episodes of high variation in recordings with a duration of less than 45 minutes.

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

The fetal behavioural state concept was used to study fetal rest-activity cycles in normal pregnancies at gestational ages of 32 and 38 weeks. In addition, it was investigated if clustering of fetal movements was already present in recordings obtained at 20 weeks. At 20 weeks, 17 periods lasting longer than 3 min were found in which fetal body movements were absent. The mean duration of these periods was 4.0 +/- 0.8 min. On the basis of random scattering of movements on a time axis, it appeared unlikely that these periods of inactivity occurred by chance alone. At 32 and 38 weeks, data on body movements were combined with data on eye movements and the FHR pattern. At 32 weeks, true fetal behavioural states were not found. The average coincidence of 1F to 4F was 58%, while only 23% was to be expected if state parameters had fulfilled state criteria purely by chance. At 38 weeks, coincidence of 1F to 4F had increased to 80% (P less than 0.001). Expected coincidence purely by chance was 30%. True fetal behavioural states were found in 17 out of 35 recordings. For transitions from 1F into 2F, the FHR changed relatively early, i.e. as first or second parameter, while for the reverse transitions it changed relatively late (P less than 0.05). There was no clearly preferred sequence for body and eye movements within transitions.

Spectral analysis of fetal heart rhythm in relation to fetal regular mouthing

Fetal heart rate variation during fetal regular mouthing in behavioural state 1F was investigated applying spectral analysis. Periods with and without fetal regular mouthing movements were compared. The power spectrum of the periods with regular mouthing movements showed a peak at the frequency of the clusters of mouthing movements which was absent in the power spectrum of the corresponding periods without movements. The oscillations in the fetal heart rate associated with this peak in the power spectrum were detectable both in the heart rate tracings obtained from the abdominal electrocardiogram and those recorded by means of wide range Doppler ultrasound.

Computer analysis of antepartum fetal heart rate: 1. Baseline determination

A consequent and reproducible determination of baseline is an essential prerequisite for objective interpretation of fetal heart rate. A fully automated off-line method of baseline determination has been developed and tested on 50 normal antepartum fetal heart rate recordings of two hours duration. The method is constructed around two functional units, a digital filter and a trim function, which interact in an iterative process. The results were evaluated in comparison with automated baseline determination according to Dawes and coworkers. A panel of 3 experts agreed that in 14 of the 50 recordings (28%), the new developed procedure resulted in a substantially better baseline fit. In the remaining 34 recordings (72%), baseline fit from both methods was judged as equivalent. The described procedure of baseline determination provides a solid base for automated detection of accelerations and decelerations in fetal heart rate recordings. It enables the study of the relation between the fetal heart rate pattern and fetal movements. Finally, it provides an objective tool for analysis of variables within the fetal heart rate with the highest predictive value with respect to fetal outcome.

Computer analysis of antepartum fetal heart rate: 2. Detection of accelerations and decelerations

Based upon a previously described procedure for automated baseline determination in antepartum fetal heart rate recordings, a programme has been developed for recognition of accelerations and decelerations. Detection of these deviations from the baseline depends on criteria for amplitude and duration, with special account for signal loss. The described automated analysis provides an objective tool for description of antepartum fetal heart rate patterns. A first evaluation with respect to its capacity to discriminate between different fetal heart rate patterns in relation to fetal rest-activity patterns shows promising results.

Automated assignment of behavioural states in the human near term fetus

Thirty-five 2-h recordings of fetal heart rate and fetal movements, made at 38-39 weeks of gestational age, have been analyzed in a partly automated procedure. Involved were 17 nulliparous and 19 multiparous women. To minimize subjectivity the classification of the heart rate was performed in a Delphi group opinion procedure consisting of three rounds. In the third round, three independent investigators classified 89.1% of the total tracing time as pattern A through D. The investigators could not classify 6.1% of the tracing time in any of the available categories. The percentages of coincidence of state parameters did not differ significantly between the fetuses of nulli- and multiparous women. Fifty percent of the fetuses showed true behavioural states, both in the nulli and the multiparous women. The percentage of time spent in state 1F was higher in the multiparous group (P less than 0.05). The other percentages of states did not differ significantly, neither did the duration of the enclosed epochs. The advantages and disadvantages of the automated assignment of fetal behavioural states are discussed.