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

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

AIM

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

METHODS

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

RESULTS

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

CONCLUSION

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

CTG Analyzer: A graphical user interface for cardiotocography

Cardiotocography (CTG) is the most commonly used test for establishing the good health of the fetus during pregnancy and labor. CTG consists in the recording of fetal heart rate (FHR; bpm) and maternal uterine contractions (UC; mmHg). FHR is characterized by baseline, baseline variability, tachycardia, bradycardia, acceleration and decelerations. Instead, UC signal is characterized by presence of contractions and contractions period. Such parameters are usually evaluated by visual inspection. However, visual analysis of CTG recordings has a well-demonstrated poor reproducibility, due to the complexity of physiological phenomena affecting fetal heart rhythm and being related to clinician's experience. Computerized tools in support of clinicians represents a possible solution for improving correctness in CTG interpretation. This paper proposes CTG Analyzer as a graphical tool for automatic and objective analysis of CTG tracings. CTG Analyzer was developed under MATLAB®; it is a very intuitive and user friendly graphical user interface. FHR time series and UC signal are represented one under the other, on a grid with reference lines, as usually done for CTG reports printed on paper. Colors help identification of FHR and UC features. Automatic analysis is based on some unchangeable features definitions provided by the FIGO guidelines, and other arbitrary settings whose default values can be changed by the user. Eventually, CTG Analyzer provides a report file listing all the quantitative results of the analysis. Thus, CTG Analyzer represents a potentially useful graphical tool for automatic and objective analysis of CTG tracings.

eCTG: an automatic procedure to extract digital cardiotocographic signals from digital images

BACKGROUND AND OBJECTIVE

Cardiotocography (CTG), consisting in the simultaneous recording of fetal heart rate (FHR) and maternal uterine contractions (UC), is a popular clinical test to assess fetal health status. Typically, CTG machines provide paper reports that are visually interpreted by clinicians. Consequently, visual CTG interpretation depends on clinician's experience and has a poor reproducibility. The lack of databases containing digital CTG signals has limited number and importance of retrospective studies finalized to set up procedures for automatic CTG analysis that could contrast visual CTG interpretation subjectivity. In order to help overcoming this problem, this study proposes an electronic procedure, termed eCTG, to extract digital CTG signals from digital CTG images, possibly obtainable by scanning paper CTG reports.

METHODS

eCTG was specifically designed to extract digital CTG signals from digital CTG images. It includes four main steps: pre-processing, Otsu's global thresholding, signal extraction and signal calibration. Its validation was performed by means of the "CTU-UHB Intrapartum Cardiotocography Database" by Physionet, that contains digital signals of 552 CTG recordings. Using MATLAB, each signal was plotted and saved as a digital image that was then submitted to eCTG. Digital CTG signals extracted by eCTG were eventually compared to corresponding signals directly available in the database. Comparison occurred in terms of signal similarity (evaluated by the correlation coefficient ρ, and the mean signal error MSE) and clinical features (including FHR baseline and variability; number, amplitude and duration of tachycardia, bradycardia, acceleration and deceleration episodes; number of early, variable, late and prolonged decelerations; and UC number, amplitude, duration and period).

RESULTS

The value of ρ between eCTG and reference signals was 0.85 (P < 10^-560) for FHR and 0.97 (P < 10^-560) for UC. On average, MSE value was 0.00 for both FHR and UC. No CTG feature was found significantly different when measured in eCTG vs. reference signals.

CONCLUSIONS

eCTG procedure is a promising useful tool to accurately extract digital FHR and UC signals from digital CTG images.

Longitudinal evaluation of computerized cardiotocographic parameters throughout pregnancy in normal fetuses: a prospective cohort study

INTRODUCTION

The longitudinal cardiotocographic (CTG) changes throughout pregnancy in normal fetuses have never been fully described. We aimed at characterizing the evolution of CTG parameters in healthy fetuses, from 24 to 41 weeks of gestation.

MATERIAL AND METHODS

A prospective cohort study was conducted in singleton fetuses without structural abnormalities on second-trimester ultrasound. At least one CTG was performed in each of the following intervals: 24-26 weeks(+6d) , 27-29 weeks(+6d) , 30-32 weeks(+6d) , 33-35 weeks(+6d) , 36-38 weeks(+6d) and ≥39 weeks; tracings were analyzed by the OMNIVIEW-SISPORTO 3.6 system. Cases of preterm delivery, fetal death, birthweight under the 10th percentile, low five-minute Apgar, umbilical artery acidemia or neonatal intensive care unit admission were subsequently excluded.

RESULTS

A total of 1049 eligible tracings were obtained from 145 fetuses. There was a significant increase over time in average long-term variability (LTV), average short-term variability (STV), number of accelerations and uterine contractions. Conversely, fetal heart rate (FHR) baseline and number of decelerations decreased. A high inter-fetal variability was observed, but there was considerable intra-fetal consistency. Fetuses showing a marked decrease in FHR baseline and those with a marked increase in average LTV had a significantly lower birthweight. Cesarean section rate was significantly higher in cases with a decrease in average STV throughout gestation.

CONCLUSIONS

This prospective longitudinal study shows an evolution in computerized CTG parameters during pregnancy, indicating the need to adapt interpretation criteria based on gestational age. The high inter-fetal variability and considerable intra-fetal consistency suggests the possible value of using each fetus as its own reference in serial assessments.

Frequency and Time Domain Analysis of Foetal Heart Rate Variability with Traditional Indexes: A Critical Survey

Monitoring of foetal heart rate and its variability (FHRV) covers an important role in assessing health of foetus. Many analysis methods have been used to get quantitative measures of FHRV. FHRV has been studied in time and in frequency domain and interesting clinical results have been obtained. Nevertheless, a standardized definition of FHRV and a precise methodology to be used for its evaluation are lacking. We carried out a literature overview about both frequency domain analysis (FDA) and time domain analysis (TDA). Then, by using simulated FHR signals, we defined the methodology for FDA. Further, employing more than 400 real FHR signals, we analysed some of the most common indexes, Short Term Variability for TDA and power content of the spectrum bands and sympathovagal balance for FDA, and evaluated their ranges of values, which in many cases are a novelty. Finally, we verified the relationship between these indexes and two important parameters: week of gestation, indicator of foetal growth, and foetal state, classified as active or at rest. Our results indicate that, according to literature, it is necessary to standardize the procedure for FHRV evaluation and to consider week of gestation and foetal state before FHR analysis.

Software for computerised analysis of cardiotocographic traces

Despite the widespread use of cardiotocography in foetal monitoring, the evaluation of foetal status suffers from a considerable inter and intra-observer variability. In order to overcome the main limitations of visual cardiotocographic assessment, computerised methods to analyse cardiotocographic recordings have been recently developed. In this study, a new software for automated analysis of foetal heart rate is presented. It allows an automatic procedure for measuring the most relevant parameters derivable from cardiotocographic traces. Simulated and real cardiotocographic traces were analysed to test software reliability. In artificial traces, we simulated a set number of events (accelerations, decelerations and contractions) to be recognised. In the case of real signals, instead, results of the computerised analysis were compared with the visual assessment performed by 18 expert clinicians and three performance indexes were computed to gain information about performances of the proposed software. The software showed preliminary performance we judged satisfactory in that the results matched completely the requirements, as proved by tests on artificial signals in which all simulated events were detected from the software. Performance indexes computed in comparison with obstetricians' evaluations are, on the contrary, not so satisfactory; in fact they led to obtain the following values of the statistical parameters: sensitivity equal to 93%, positive predictive value equal to 82% and accuracy equal to 77%. Very probably this arises from the high variability of trace annotation carried out by clinicians.

Fetal brain sonography and fetal heart rate patterns in the preterm fetus

OBJECTIVE

The objective of the study was to study whether peri- and intraventricular echodensities in the brain of fetuses at risk for preterm birth are associated with changes in fetal heart rate (FHR) parameters.

STUDY DESIGN

Twenty preterm fetuses with peri- and intraventricular echodensities detected by transvaginal ultrasonography were matched with 20 fetuses without echodensities for gestational age, growth parameters, clinical disease, and maternal medication. Baseline FHR, long- and short-term variability, and the presence of accelerations and decelerations were analyzed with a computerized system and compared with the Wilcoxon matched-pairs signed-rank test. Both cases and controls were compared with a normal population.

RESULTS

No statistical differences in FHR parameters were found between cases with and controls without peri- and intraventricular echodensities. Both cases and controls had lower long- and short-term variabilities than the normal population.

CONCLUSION

No association between the presence of peri- and intraventricular echodensities and specific FHR changes was demonstrated.

Identification of fetal sufferance antepartum through a multiparametric analysis and a support vector machine

The present work is concerned with the automatic identification of fetal sufferance in intrauterine growth retarded (IUGR) fetuses, based on a multiparametric analysis of cardiotocographic recordings feeding a neural classifier. As classification tool, we propose a SVM (support vector machine), which receives the set of linear and nonlinear parameters extracted from the fetal heart rate signal (FHR) as input and gives the indication of fetal distress as output. SVM is a powerful supervised learning algorithm belonging to the statistical learning theory. It minimizes the structural risk performance in various classification problems. Three SVMs are built with different kernels. Their training set includes 70 cases: 35 normal and 35 IUGR suffering fetuses. Classification results obtained with a 2nd order polynomial kernel, on a test set of 30 unknown cases, show good values of accuracy, specificity and sensitivity. The SVM performance is very similar to that obtained with multilayer perceptron and neurofuzzy classifiers proposed in previous works. The introduction of a hybrid unsupervised/supervised learning scheme integrating independent component analysis (ICA) with SVM will be the natural development of this work with a further improvement of the diagnostic ability of the system.

Prediction of neonatal state by computer analysis of fetal heart rate tracings: the antepartum arm of the SisPorto® multicentre validation study

OBJECTIVE

To evaluate the capacity of computer analysis of antepartum cardiotocographs performed by SisPorto 2.0 in predicting neonatal outcome.

STUDY DESIGN

A prospective observational study was conducted in eight tertiary care centres in Europe and Australia, involving pregnant women in the absence of labor, scheduled for elective caesarean section, whose last fetal heart rate (FHR) tracing was performed within 4h of delivery. After exclusion of fetal malformations, multiple pregnancies, tracings with less than 30 min, tracings with more than 15% signal loss, difficult fetal extractions, and anesthesia complications, a total of 345 cases were analyzed. Computer quantification of cardiotocographic parameters was compared with newborn Apgar score, umbilical artery pH, metabolic acidosis and neonatal hypoxic-ischemic encephalopathy, by means of receiver operating characteristic (ROC) curves.

RESULTS

Acceleration number, mean short-term variability, percentage of abnormal short-term variability and percentage of abnormal long-term variability had an excellent discriminative capacity to predict 1-min Apgar scores under or equal to 4 (areas under the ROC curve 0.96-1.00). The same parameters showed a slightly lower capacity to predict 5-min Apgar scores under or equal to 6 (areas under the ROC curve 0.81-0.89). The best cut-off values for these parameters, derived from the previously referred calculations, detected all cases of hypoxic-ischemic encephalopathy (n = 2). Cardiotocographic parameters showed a lower discriminative capacity in prediction of umbilical artery pH <7.20 (maximum area under the ROC curve 0.66) and <7.15 (maximum area under the ROC curve 0.69).

CONCLUSIONS

Computerized quantification of accelerations and variability in the antepartum allows a good prediction of 1 and 5-min Apgar scores, and to a much lesser degree umbilical artery pH.

Linear and nonlinear parameters for the analysis of fetal heart rate signal from cardiotocographic recordings

Antepartum fetal monitoring based on the classical cardiotocography (CTG) is a noninvasive and simple tool for checking fetal status. Its introduction in the clinical routine limited the occurrence of fetal problems leading to a reduction of the precocious child mortality. Nevertheless, very poor indications on fetal pathologies can be inferred from the even automatic CTG analysis methods, which are actually employed. The feeling is that fetal heart rate (FHR) signals and uterine contractions carry much more information on fetal state than is usually extracted by classical analysis methods. In particular, FHR signal contains indications about the neural development of the fetus. However, the methods actually adopted for judging a CTG trace as "abnormal" give weak predictive indications about fetal dangers. We propose a new methodological approach for the CTG monitoring, based on a multiparametric FHR analysis, which includes spectral parameters from autoregressive models and nonlinear algorithms (approximate entropy). This preliminary study considers 14 normal fetuses, eight cases of gestational (maternal) diabetes, and 13 intrauterine growth retarded fetuses. A comparison with the traditional time domain analysis is also included. This paper shows that the proposed new parameters are able to separate normal from pathological fetuses. Results constitute the first step for realizing a new clinical classification system for the early diagnosis of most common fetal pathologies.

Antepartum computerized CTG and neonatal acid-base status at birth

OBJECTIVE

To assess the correlation between individual computerized cardiotocography (cCTG) variables and acid-base status at birth before the first breathing in uncomplicated term pregnancy delivered by cesarean section.

STUDY DESIGN

A retrospective cohort study.

SUBJECTS AND METHODS

Seventy singleton normal pregnancies delivered by elective cesarean section. The last antepartum cCTG performed within 4 h from delivery by the System 8002 (Oxford Sonicaid, UK) was correlated to umbilical blood gas analysis (UBGA) values (AVL compact 2 analyser). Considering blood gas analysis values as dependent and individual cCTG parameters as independent variables the best regression subsets followed by a backward stepwise linear regression was used.

RESULTS

There was no significant correlation of cCTG parameters with any of the values of blood gas analysis. However, when neonatal conditions, as expressed by arterial pH > 7.20, Becf > - 4.0 mmol/l and Apgar score at 5 min > 7, were taken as an end-point, they could be predicted by Acc15 and FM/hour (sensitivity: 35%, positive predictive value: 92%, cut-off > 7 and 67%, 92%, > 21, respectively).

CONCLUSION

In uncomplicated pregnancies, the prospect of a vigorous newborn seems particularly associated with the presence of Acc > 15 and FM/hour > 21.