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1

Fetal heart rate estimation using fractional Fourier transform and wavelet analysis

Jaba Deva Krupa Abel, Dhanalakshmi Samiappan, Sanjana N.L., Manivannan Naveen, Kumar Ramamoorthy, Tripathy Saswati

Biocybernetics and Biomedical Engineering

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2021

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Vol. 41, no. 4

1533--1547

EN

Objective: Monitoring fetal cardiac activity during pregnancy is a critical part of assessing the fetus’s health. Non-invasive fetal electrocardiogram (NIFECG) is a safe emerging fetal cardiac monitoring approach receiving considerable interest. This paper proposes an effective way to separate the fetal ECG signal from the single-channel abdominal ECG signals. Methods: The paper proposes a novel algorithm based on time-frequency analysis combining fractional Fourier transform (FrFT) and wavelet analysis to extract fetal ECG from abdominal signals at higher accuracy. The abdominal signals acquired from pregnant women are preprocessed and subjected to suppressing maternal ECG using fractional Fourier transform and maximum likelihood estimate. The estimated maternal signal is removed from the abdominal ECG. The residue is processed using wavelet decomposition to obtain a clean fetal ECG and calculate fetal heart rate. Results: The proposed algorithm’s performance is validated using signals from the Daisy database and Physionet challenge 2013 set-a dataset. Real-time signals acquired using Powerlab data acquisition hardware are also included for validation. The obtained results show that the proposed algorithm can effectively extract the fetal ECG and accurately estimate the fetal heart rate. Conclusion: The proposed method is a promising and straightforward algorithm for FECG extraction. Fractional Fourier transform maps the time domain abdominal signal into the fractional frequency domain, distinguishing the fetal and maternal ECG. The Wavelet transform can efficiently denoise the residue abdominal signal and provides a clean fetal ECG. The proposed approach achieves 98.12% of accuracy, 98.85% of sensitivity, 99.16% of positive predictive value, and 99.42% of F1 measure.

2

Evaluating the fetal heart rate baseline estimation algorithms by their influence on detection of clinically important patterns

Jezewski J., Horoba K., Roj D., Wrobel J., Kupka T., Matonia A.

Biocybernetics and Biomedical Engineering

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2016

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Vol. 36, no. 4

562--573

EN

A correctly estimated component of fetal heart rate signal (FHR) – so called baseline – is a precondition for proper recognition of acceleration and deceleration patterns. A number of various algorithms for estimating the FHR baseline was proposed so far. However, there is no reference standard enabling their objective evaluation, and thus no methodology of comparing the different algorithms still exists. In this paper we propose a method for evaluation of automatically determined baseline in reference to a set of experts, based on ten separate groups of signals comprising typical variability patterns observed in the fetal heart rate. As it was proposed earlier [1], the given algorithm is evaluated based on the characteristic patterns detected using the obtained baseline, instead of direct analysis of the baseline shape. For the purpose of quantitative assessment of the estimated baseline a new synthetic inconsistency coefficient was applied. The proposed methodology enabled to evaluate eleven well-known algorithms. We believe that the method will be a valuable tool for assessment of the existing algorithms, as well as for developing the new ones.

3

Automated detection of fetal movements in Doppler ultrasound signals versus maternal perception

Wróbel J., Kupka T., Horoba K., Matonia A., Roj D., Jeżewski J.

Journal of Medical Informatics & Technologies

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2014

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Vol. 23

43--50

EN

Analysis of movement activity is important since it enables detection of nonreactive fetal heart rate recordings. The aim of the study was to develop an algorithm for automated detection of the fetal movement activity (actogram), based on analysis of the Doppler ultrasound signal, and to evaluate a reliability of the actogram as a source of information about the fetal movements. Bandpass filtering (20-80 Hz) was used to separate the actogram signal describing the fetal movement activity. Simultaneously there were recorded the markers of fetal movements perceived by mother, being the reference information. For the determination of the binary actogram, the authors proposed an algorithm in which the classification threshold was estimated at the beginning of each recording and was adaptively modified during its duration. The algorithm ensured detection of up to 89% of movement episodes corresponding to movements perceived by mother. At the same time almost as high number of episodes not related to the reference information was recognized. Obtained results revealed that the automated analysis of fetal movements is characterized by much higher sensitivity of movement episode detection compared to the maternal perception.

4

Comparison of instantaneous fetal heart rate extracted from abdominal and direct fetal electrocardiograms

Matonia A., Kupka T., Jezewski J., Momot A., Jeżewski M., Bernys M.

Journal of Medical Informatics & Technologies

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2012

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Vol. 19

101--107

EN

This work is an attempt to assess the reliability of indirect abdominal electrocardiography as an alternative technique of fetal monitoring. As a reference signal we used the simultaneously acquired direct fetal electrocardiogram. Each recording consisted of four signals acquired from maternal abdomen and the reference signal acquired directly from fetal head. The first stage of our study concerned the signal loss episodes. In order to reduce the influence of incorrectly detected R-waves, some certain validation rules were applied. In the second stage, the corresponding intervals determined on basis of both acquisition methods were matched and the accuracy of fetal heart rate measurement was evaluated. Although the accuracy of abdominal electrocardiography turned out to be slightly lower than reported for ultrasound method, it still has some unique features deciding of its prevalence in a certain circumstances.

5

A routing protocol for wireless network of bedside monitors in fetal surveillance system

Seredynski R., Horoba K., Roj D., Bernys M., Przybyla T., Jezewski J.

Journal of Medical Informatics & Technologies

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2012

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Vol. 21

27--33

EN

The paper presents the methodology of wireless network design, developed according to the requirements originating from existing wired fetal surveillance systems. The proposed network structure is based on popular radio frequency modules, operating in 433/866MHz band. The described solution is a simple and cost effective alternative to the wired networks, and it will vastly increase the mobility of fetal monitors. The authors also describe software tools which were designed for this purpose and the results of simulations performed on their basis.

6

Investigation of optical detection strategies for transabdominal fetal heart rate detection using three-layered tissue model and Monte Carlo simulation

Gan K. B., Zahedi E. Z., Mohd-Ali M. A.

Optica Applicata

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2011

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Vol. 41, nr 4

885--896

EN

In this paper, the Monte Carlo technique is used to determine the optical detection strategies in three-layered (maternal, amniotic fluid and fetal) tissue model. This model is utilized to estimate the transabdominal optical power and optimum source-detector (S-D) separation. Results based on the launching of 2 million photons with 1 mW optical power showed that the expected optical power output is in the range of 10-6-10-10 W/cm2 depending on S-D separation. Considering the limit of the signal processing methods (such as adaptive noise cancelling) and the use of silicon photodetector, an S-D separation of 4 cm has been selected as a practical compromise between signal level and percentage of optical power (70%) coming from the fetal layer. Based on these findings, transabdominal fetal heart rate detection system using NIR and adaptive filtering can be designed and developed.

7

Fuzzy prediction of fetal acidemia

Czabański R., Roj D., Jeżewski J., Horoba K., Jeżewski M.

Journal of Medical Informatics & Technologies

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2011

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Vol. 17

81--87

EN

Cardiotocography is the primary method for biophysical assessment of a fetal state. It is based mainly on the recording and analysis of fetal heart rate signal (FHR). Computer systems for fetal monitoring provide a quantitative description of FHR signals, however the effective methods for their qualitative assessment are still needed. The measurements of hydronium ions concentration (pH) in newborn cord blood is considered as the objective indicator of the fetal state. Improper pH level is a symptom of acidemia being the result of fetal hypoxia. The paper proposes a twostep analysis of signals allowing for effective prediction of the acidemia risk. The first step consists in the fuzzy classification of FHR signals. The task of fuzzy inference is to indicate signals that according to the FIGO guidelines represent the fetal wellbeing. These recordings are eliminated from the further classification with Lagrangian Support Vector Machines. The proposed procedure was evaluated using data collected with computerized fetal surveillance system. The classification results confirmed the high quality of the proposed fuzzy method of fetal state evaluation.

8

Application of generalized filters for estimation of fetal heart rate baseline

Pander T., Przybyla T., Wrobel J., Jezewski J., Roj D.

Journal of Medical Informatics & Technologies

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2011

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Vol. 17

73--79

EN

This paper addresses the problem of impulsive noise cancellation in digital signal area. The myriad and meridian filters are the type of robust filters which are very useful in suppressing the impulsive type of noise. The cost functions of theses filters have very similar structure. In this paper the generalized filter based on Lp norm is presented. The proposed filter operates in a wide range of impulsive noise due to the proper adjustment of p in the Lp norm. The presented filter is applied to suppress an impulsive noise in fetal heart rate (FHR) signal. Simulation results confirm the validity of the proposed filter.

9

Improving the periodicity measurement in fetal heart activity signal

Roj D., Wróbel J., Horoba K., Przybyła T., Kupka T.

Journal of Medical Informatics & Technologies

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2010

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Vol. 16

19--26

EN

In this paper we discussed the influence of preliminary processing of the ultrasound Doppler signal on accuracy of the fetal heart rate estimation as well as on reliability of the FHR instantaneous variability assessment. We attempted to develop an optimal processing channel of US Doppler signal in order to measure the periodicity of fetal heart activity with accuracy as close as possible to that ensured by FECG. The FHR values determined from the US signal were compared to the reference data obtained from direct FECG. In a final evaluation we used the parameters describing the FHR variability as the clinically important signal features being the most sensitive to any periodicity inaccuracy. The results proved that an application of proposed algorithms improves the accuracy of interval measurements and FHR instantaneous variability assessment in relation to the new-generation fetal monitors.

10

Evaluation of predictive capabilities of quantitative cardiotocographic signal features

Czabański R., Jeżewski M., Roj D., Szaszkowski Z., Kupka T., Wróbel J.

Journal of Medical Informatics & Technologies

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2010

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Vol. 16

11--17

EN

Cardiotocography (CTG) is the main method of assessment of the fetal state during pregnancy and labour used in clinical practice. It is based on quantitative analysis of fetal heart rate, fetal movements and uterine contractions signals. The evaluation of the CTG signals can be made using criteria recommended by International Federation of Obstetrics and Gynecology. Nevertheless, the diagnosis verification is possible only after the delivery on the basis of newborn assessment. In the proposed work we evaluated the capacity of quantitative analysis of CTG traces in predicting fetal outcome. The relationship between CTG signal features and attributes of fetal outcome was assessed on the basis of ROC curves analysis. The obtained results indicate the adequate predictive capabilities of the selected CTG features especially for fetal outcome assessed with Apgar score and suggest the necessity of applying the criteria for the CTG traces evaluation that are related to the gestational age. Our study also shows the value of the CTG monitoring as a screening procedure providing appropriate confirmation of fetal wellbeing.

11

Analysis of extracted cardiotocographic signal features to improve automated prediction of fetal outcome

Jeżewski M., Czabański R., Wróbel J., Horoba K.

Biocybernetics and Biomedical Engineering

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2010

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Vol. 30, no. 4

29-47

EN

Cardiotocographic monitoring based on automated analysis of the fetal heart rate (FHR) signal is widely used for fetal assessment. However, the conclusion generation system is still needed to improve the abnormal fetal outcome prediction. Classification of the signals according to the predicted fetal outcome by means of neural networks is presented in this paper. Multi-layer perceptron neural networks were learned through seventeen time-domain signal features extracted during computerized analysis of 749 traces from 103 patients. The analysis included estimation of the FHR baseline, detection of acceleration and deceleration patterns as well as measurement of the instantaneous FHR variability. All the traces were retrospectively verified by the real fetal outcome defined by newborn delivery data. Influence of numerical and categorical representation of the input signal features, different data sets during learning, and gestational age as additional information, were investigated. We achieved the best sensitivity and specificity for the neural networks fed with numerical input variables together with additional information on the gestational age in the categorical form.

12

Fuzzy system for evaluation of fetal heart rate signals using FIGO criteria

Czabański R., Jeżewski M., Wróbel J., Jeżewski J., Horoba K.

Journal of Medical Informatics & Technologies

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2009

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Vol. 13

189--194

EN

Cardiotocography is a biophysical method of fetal monitoring during pregnancy and labour. It is mainly based on recording and analysis of fetal heart activity. The computerized fetal monitoring systems provide the quantitative description of the recorded signals but the effective methods supporting the conclusion generation are still needed. The evaluation of the signal can be made using criteria recommended by FIGO. Nevertheless, the quantitative description of the traces is inconsistent with qualitative nature of the obstetric knowledge. Therefore, we applied the fuzzy system based on Takagi-Sugeno-Kang model to evaluate and classify signals. FIGO guidelines were used for developing a set of fuzzy conditional rules defining the system performance. The proposed system was evaluated using data collected with computerized fetal surveillance system – MONAKO. The classification results confirm the improvement of the fetal state evaluation quality while using the proposed fuzzy system support.

13

The influence of window size of autocorrelation function on fetal heart rate variability measurement using the Doppler ultrasound signal

Roj D., Fuchs T., Przybyła T., Jeżewski M., Matonia A., Gacek A.

Journal of Medical Informatics & Technologies

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2008

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Vol. 12

111--116

EN

Commonly used noninvasive fetal monitoring is based on fetal heart rate (FHR) variability analysis of the Doppler ultrasound signal coming from the mechanical activity of the fetal heart. Estimation of periodicity of acquired signals using the autocorrelation technique is very important. The determination of cardiac intervals using the Doppler signal is more difficult than in electrocardiography, where the R-waves are evident. We investigated the influence of the autocorrelation window size on the FHR variability analysis. The indices describing the FHR variability calculated for signals obtained using two different autocorrelation techniques with various window lengths were compared with the reference ones obtained from fetal electrocardiogram. The optimal window was a compromise between artifacts resistance and the averaging level of instantaneous variability.

14

Recognition of early symptoms of fetal distress with on-line analysis of bioelectrical signals from maternal abdomen

Gacek A., Matonia A., Jeżewski J., Kupka T.

Biocybernetics and Biomedical Engineering

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2007

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Vol. 27, no. 1-2

207-216

EN

Conventional fetal monitoring for recognition of fetal distress is based on ultrasound Doppler technique. The new approach proposed in this work relies on analysis of bioelectrical signals recorded from the maternal abdominal wall. Fetal electrocardiogram and uterine electrical signal are extracted from abdominal signals using advanced instrumentation and algorithms for signal processing. Evaluation of the fetal heart rate variability with an additional analysis of fetal electrocardiogram morphology is expected to ensure early detection of fetal hypoxia symptoms and, finally, an appropriate obstetrical intervention.

15

The fetal heart rate estimation based on continuous ultrasonic Doppler data

Kret T., Kałużyński K.

Biocybernetics and Biomedical Engineering

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2006

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Vol. 26, no. 3

49-56

EN

Two methods to compute the fetal heart rate based on the analysis of Doppler signals obtained using continuous wave ultrasound were studied. The first uses bandpass filtering, directional signal separation and computation of the autocorrelation coefficient of the envelope of a single directional Doppler signal. The other uses discrete wavelet decomposition and reconstruction of a single directional signal with Daubechies db 10 wavelet family, with subsequent computation of the autocorrelation coefficient of the envelope of the reconstructed signal details for various scales. The results indicate that the discrete wavelet decomposition method is a suitable tool for fetal heart rate determination. It results in a more consistent fetal heart rate trace than the bandpass filtering approach.

16

Monitoring of fetal movements based on actogram signal analysis

Kupka T., Matonia A., Wróbel J., Horoba K., Jeżewski J.

Journal of Medical Informatics & Technologies

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2004

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Vol. 8

MM119--128

EN

At present, biophysical fetal monitoring relies mainly on evaluation of a fetal heart rate (FHR). Absence of the FHR variability indicates central nervous system depression associated with hypoxia. The analysis of fetal heart rate segments identified with the aid of information on fetal movement activity provides much better results than analysis of the whole signal. Automatic recording of the fetal movement activity in a form of actogram signal provided by new models of fetal monitors becomes very common. For evaluation of information content of the actogram signal, the measurement instrumentation has been developed. The examined group comprised 20 patients and the total time of recording was 10 hours. Correlation between movements observed by clinical experts on ultrasonographic image and actogram trace recorded by fetal monitor was analysed. Although for head, arms, legs and trunk movements just visual analysis let observe their correlation with actogram signal, but in case of breathing movement no correlation was noted. Depending on movement type the detection efficiency was in range from 54 % to 80 %.

17

Ultrasonographic validation of the software system for online analysis of ultrasonic Doppler signals of fetal activity

Kret T., Kałużyński K.

Elektronika : konstrukcje, technologie, zastosowania

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2004

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Vol. 45, nr 8-9

127-129

EN

Fetal motor activity (pseudobreathing movements, trunk and limb movements) and the fetal heart rate are important indicators of fetal well-being. The software developed using the LabVIEW environment processes in real time Doppler signals acquired from the CW fetal Doppler activity monitor via the PC sound card. Displacements of the structures, velocities and accelerations of these displacements as well as histograms of the velocities and accelerations are computed. The fetal heart rate and breathing movements are determined. The software performance was tested against ultrasonographic recordings. Four pregnancies were submitted to a 15-20 minutes long examination. The ultrasonographic images and Doppler quadrature data were taped simultaneously with Hi-Fi video recorder, then used as signal source for laboratory tests of the software. The movements detected with the software environment were compared with the concurrent USG images. The experiments show that the elaborated software is capable of detecting different kinds of fetal movements. Some artifacts, specifically those resulting from maternal movements, may be eliminated on the basis of their amplitude. The software is a promising diagnostic tool for obstetrics.

PL

Aktywność ruchowa płodu (ruchy pseudooddechowe, ruchy tułowia i kończyn) oraz rytm serca są ważnymi wskaźnikami stanu płodu. Oprogramowanie stworzone z użyciem środowiska LabVIEW przetwarza, w czasie rzeczywistym, sygnały dopplerowskie uzyskiwane z monitora aktywności ruchowej płodu z falą ciągłą przez kartę dźwiękową komputera PC. Wyznaczane są ruchy płodu, prędkości i przyśpieszenia tych ruchów, jak również histogramy prędkości i przyśpieszeń. Wykrywane są rytm serca płodu, jak również ruchy pseudooddechowe. Wyniki uzyskiwane przez oprogramowanie porównano z wynikami obserwacji ultrasonograficznej. Cztery przypadki ciąż bez powikłań zostały poddane 15-20 minutowemu badaniu. Obrazy ultrasonograficzne i kwadraturowe sygnały dopplerowskie były rejestrowane jednocześnie z użyciem magnetowidu Hi-Fi, następnie zostały użyte jako źródło sygnału podczas testów oprogramowania w warunkach laboratoryjnych. Opracowane oprogramowanie wykrywa różne rodzaje ruchów płodu. Niektóre zakłócenia, szczególnie te wynikające z ruchów matki, mogą być eliminowane w oparciu o ich amplitudę. Oprogramowanie jest obiecującym narzędziem w diagnostyce położniczej.

18

Antenatal fetal surveillance using bioelectrical signals

Matonia A., Bernyś M., Kupka T., Jeżewski J., Horoba K.

Elektronika : konstrukcje, technologie, zastosowania

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2004

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Vol. 45, nr 8-9

110-113

EN

A new approach alternative to cardiotocographic conventional letal monitoring is presented. It relies upon analysis of bioelectrical signals recorded from maternal abdominal wall. Due to strong interferences present in abdominal signal advanced methods of signal processing have been developed to extract letal electrocardiogram and uterine electrical activity signal. The described system allows replacement of more expensive cardiotocographic instrumentation based on ultrasound. Doppler method and ensures the higher diagnostic capacity at the same time.

PL

W pracy przedstawione zostało nowe, alternatywne w stosunku do tradycyjnej kardiotokogralii, podejście do monitorowania stanu płodu w okresie przedporodowym. Zostało ono oparte o rejestrację i analizę biosygnałów rejestrowanych z powierzchni brzucha matki. Występujące w tych sygnałach zakłócenia wymagają stosowania zaawansowanych technik przetwarzania sygnałów w celu wydobycia użytecznej informacji: elektrokardiogramu płodu i sygnału elektrycznej aktywności mięśnia macicy. Opracowany został uniwersalny system do monitorowania płodu pozwalający zastąpić kosztowne aparaty kardiotokograliczne wykorzystujące technikę ultradźwiękową, a zapewniający przy tym znacznie większe możliwości oceny i detekcji stanu zagrożenia płodu.

19

Online analysis of the ultrasonic Doppler signals of the fetal motor activity in the LabVIEW environment

Kret T., Kałużyński K.

Biocybernetics and Biomedical Engineering

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2004

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Vol. 24, no. 2

41-49

EN

Fetal motor activity and the fetal heart rate are important indicators of fetal well-being. The motor activity consist of pseudobreathing movements, trunk and limb movements. These movements can be detected using the ultrasonic Doppler method. The software developed using the LabVIEW environment processes in real time Doppler signals acquired via the PC sound card. Displacements of the structures, velocities and accelerations of these displacements as well as histograms of the velocities and accelerations are computed. Spectral analysis of the chest displacement signal allows determining the rhythm of pseudobreatching movements. The autocorrelation function is used to compute the fetal heart rate. The software was tested on simulated signals and real fetal Doppler signals.

20

Combined analysis of fetal electrocardiogram and systolic time intervals

Matonia A., Jeżewski J., Kupka T., Horoba K., Wróbel J., Widera M.

Journal of Medical Informatics & Technologies

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2003

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Vol. 6

IT27--34

EN

Cardiotocography as a simultaneous recording of fetal heart rate (FHR) and uterine contraction activity is a basic method of evaluation of fetal condition. Correct variability of the fetal heart rate is an indirect sign of adequate oxygenation of a fetus. Unfortunately, the reverse case is not always true, signs suggesting pathological changes can also appear in recording when the fetal is not at risk. The cardiotocography shall then be recognized as a more screening than diagnostic method. It will be interesting to develop a non-invasive method being complementary to routine cardiotocography. This method should allow the adequate prediction of a bad neonatal outcome when the test is abnormal. The paper shows the system that makes possible cardiotocograms analysis in parallel with the assessment of additional parameters determined from comparison of mechanical and electrical fetal heart activity signals. The studies are aimed at development of set of parameters that are high correlated with clinical outcome.