The most commonly used method of fetal monitoring is based on heart activity analysis. Computer-aided fetal monitoring system enables extraction of clinically important information hidden for visual interpretation-the instantaneous fetal heart rate (FHR) variability. Today's fetal monitors are based on monitoring of mechanical activity of the fetal heart by means of Doppler ultrasound technique. The FHR is determined using autocorrelation methods, and thus it has a form of evenly spaced-every 250 ms-instantaneous measurements, where some of which are incorrect or duplicate. The parameters describing a beat-to-beat FHR variability calculated from such a signal show significant errors. The aim of our research was to develop new analysis methods that will both improve an accuracy of the FHR determination and provide FHR representation as time series of events. The study was carried out on simultaneously recorded (during labor) Doppler ultrasound signal and the reference direct fetal electrocardiogram Two subranges of Doppler bandwidths were separated to describe heart wall movements and valve motions. After reduction of signal complexity by determining the Doppler ultrasound envelope, the signal was analyzed to determine the FHR. The autocorrelation method supported by a trapezoidal prediction function was used. In the final stage, two different methods were developed to provide signal representation as time series of events: the first using correction of duplicate measurements and the second based on segmentation of instantaneous periodicity measurements. Thus, it ensured the mean heart interval measurement error of only 1.35 ms. In a case of beat-to-beat variability assessment the errors ranged from -1.9% to -10.1%. Comparing the obtained values to other published results clearly confirms that the new methods provides a higher accuracy of an interval measurement and a better reliability of the FHR variability estimation.

Department of Cybernetics and Biomedical Engineering VSB Technical University of Ostrava 70800 Ostrava Poruba Czech Republic

Department of Cybernetics Nanotechnology and Data Processing Silesian University of Technology PL44100 Gliwice Poland

Łukasiewicz Research Network Institute of Medical Technology and Equipment PL41800 Zabrze Poland

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Horoba K., Wrobel J., Jezewski J., Kupka T., Roj D., Jezewski M. Automated detection of uterine contractions in tocography signals–comparison of algorithms. Biocybern. Biomed. Eng. 2016;36:610–618. doi: 10.1016/j.bbe.2016.08.005. DOI

Jezewski J., Matonia A., Czabanski R., Horoba K., Kupka T. Classification of Uterine Electrical Activity Patterns for Early Detection of Preterm Birth. In: Burduk R., Jackowski K., Kurzynski M., Wozniak M., Zolnierek A., editors. Computer Recognition Systems 8–CORES 2013. Volume 226. Springer; Heidelberg, Germany: 2013. pp. 559–568. Advances in Intelligent Systems and Computing.

Jezewski J., Wrobel J., Horoba K., Gacek A., Sikora J. Fetal heart rate variability: Clinical experts versus computerized system interpretation; Proceedings of the 24th International Conference of IEEE Engineering in Medicine and Biology Society; Houston, TX, USA. 23–26 October 2002; pp. 1617–1618.

Horoba K., Jezewski J., Matonia A., Wrobel J., Czabanski R., Jezewski M. Early predicting a risk of preterm labour by analysis of antepartum electrohysterograhic signals. Biocybern. Biomed. Eng. 2016;36:574–583. doi: 10.1016/j.bbe.2016.06.004. DOI

Sikora J., Matonia A., Czabanski R., Horoba K., Jezewski J., Kupka T. Recognition of Premature Threatening Labour Symptoms from Bioelectrical Uterine Activity Signals. Arch. Perinat Med. 2011;17:97–103.

Kording F., Schoennagel B., Lund G., Ueberle F., Jung C., Adam G., Yamamura J. Doppler ultrasound compared with electrocardiogram and pulse oximetry cardiac triggering: A pilot study. Magn. Reson. Med. 2014;74:1257–1265. doi: 10.1002/mrm.25502. PubMed DOI

Jaros R., Martinek R., Kahankova R. Non-Adaptive Methods for Fetal ECG Signal Processing: A Review and Appraisal. Sensors. 2018;18:3648. doi: 10.3390/s18113648. PubMed DOI PMC

Van Scheepen J.A.M., Koster M.P.H., Vasak B., Redman C., Franx A., Georgieva A. Effect of signal acquisition method on the fetal heart rate analysis with phase rectified signal averaging. Physiol. Meas. 2016;37:2245–2259. doi: 10.1088/1361-6579/37/12/2245. PubMed DOI

Jezewski J., Horoba K., Roj D., Wrobel J., Kupka T., Matonia A. Evaluating the fetal heart rate baseline estimation algorithms by their influence on detection of clinically important patterns. Biocybern. Biomed. Eng. 2016;36:562–573. doi: 10.1016/j.bbe.2016.06.003. DOI

Jezewski J., Horoba K., Matonia A., Gacek A., Bernyś M. A new approach to cardiotocographic fetal monitoring based on analysis of bioelectrical signals; Proceedings of the 25th International Conference of IEEE Engineering in Medicine and Biology Society; Cancum, Mexico. 1–4 September 2003; pp. 3145–3149.

Jezewski J., Wrobel J., Matonia A., Horoba K., Martinek R., Kupka T., Jezewski M. Is abdominal fetal electrocardiography an alternative to Doppler ultrasound for FHR variability evaluation? Front. Physiol. 2017;8:305. doi: 10.3389/fphys.2017.00305. PubMed DOI PMC

Kahankova R., Jezewski J., Nedoma J., Jezewski M., Fajkus M., Kawala-Janik A., Wen H., Martinek R. Influence of gestation age on the performance of adaptive systems for fetal ECG extraction. Adv. Electr. Electron. Eng. 2017;15:491–501. doi: 10.15598/aeee.v15i3.2207. DOI

Jezewski J., Matonia A., Kupka T., Roj D., Czabański R. Determination of the fetal heart rate from abdominal signals: Evaluation of beat-to-beat accuracy in relation to the direct fetal electrocardiogram. Biomed. Eng. 2012;57:383–394. doi: 10.1515/bmt-2011-0130. PubMed DOI

Kahankova R., Jaros R., Martinek R., Jezewski J., Wen H., Jezewski M., Kawala-Janik A. Non-Adaptive Methods of Fetal ECG Signal Processing. Adv. Electr. Electron. Eng. 2017;15:476–490. doi: 10.15598/aeee.v15i3.2196. DOI

Martinek R., Kahankova R., Jezewski J., Jaros R., Mohylova J., Fajkus M., Nedoma J., Janku P., Nazeran H. Comparative Effectiveness of ICA and PCA in Extraction of fECG from aECG Signals: Towards Multichannel Non-Invasive fHR Monitoring. Front. Physiol. 2018;9:648. doi: 10.3389/fphys.2018.00648. PubMed DOI PMC

Docker M.F. Doppler ultrasound monitoring technology. Br. J. Obstet. Gynaecol. 1993;100:18–20. doi: 10.1111/j.1471-0528.1993.tb10630.x. PubMed DOI

Khandoker A.H., Kimura Y., Ito T., Palaniswami M. Non-invasive determination of electromechanical time intervals of cardiac cycle using abdominal ECG and Doppler ultrasound signals from fetal hearts. Comput. Cardiol. 2007;34:657–660.

Abdulhay E.W., Oweis R.J., Alhaddad A.M., Sublaban F.N., Radwan M.A., Almasaeed H.M. Non-Invasive Fetal Heart Rate Monitoring Techniques: Review Article. Biomed. Sci. Eng. 2014;2:53–67.

Alnuaimi S., Jimaa S., Khandoker A.H. A Review of Fetal cardiac Doppler Signal Processing for Screening Foetal Well Being. Front. Bioeng. Biotechnol. 2017;5:82. doi: 10.3389/fbioe.2017.00082. PubMed DOI PMC

Kording F., Schoennagel B., Tavares de Sousa M., Fehrs K., Adam G., Yamamura J., Ruprecht C. Evaluation of a Portable Doppler Ultrasound Gating Device for Fetal Cardiac MR Imaging: Initial Results at 1.5T and 3T. Magn. Reson. Med. Sci. 2018;17:308. doi: 10.2463/mrms.mp.2017-0100. PubMed DOI PMC

Mert A., Sezdi M., Akan A. A test and simulation device for Doppler-based fetal heart rate monitoring. Turk. J. Electr. Eng. Comput. Sci. 2015;23:1187–1194. doi: 10.3906/elk-1306-224. DOI

Karjadi M., Salahuddin N.S., Wibowo E.P., Afandi H. Digital Filter Design of Infinite Impulse Response (IIR) Infrasound to Detect Fetal Heart Rate. Int. J. Eng. Res. Sci. 2016;2:25–38.

Kupka T., Jeżewski J., Matonia A., Horoba K., Wróbel J. Timing events in Doppler ultrasound signal of fetal heart activity; Proceedings of the 26th International Conference of IEEE Engineering in Medicine and Biology Society; San Francisco, CA, USA. 1–4 September 2004; pp. 337–340. PubMed

Voicu I., Girault J.M., Roussel C., Decock A., Kouame D. Robust estimation of fetal heart rate from US Doppler signals. Phys. Procedia. 2010;3:691–699. doi: 10.1016/j.phpro.2010.01.087. DOI

Marzbanrad F., Kimura Y., Funamoto K., Sugibayashi R., Endo M., Ito T., Palaniswami M., Khandoker A.H. Automated Estimation of Fetal Cardiac Timing Events From Doppler Ultrasound Signal Using Hybrid Models. IEEE J. Biomed. Health Inform. 2014;18:1169–1177. doi: 10.1109/JBHI.2013.2286155. PubMed DOI

Marzbanrad F., Kimura Y., Funamoto K., Oshio S., Endo M., Sato N., Palaniswami M., Khandoker A.H. Model-Based Estimation of Aortic and Mitral Valves Opening and Closing Timings in Developing Human Fetuses. IEEE J. Biomed. Health Inform. 2016;20:240–248. doi: 10.1109/JBHI.2014.2363452. PubMed DOI

Marzbanrad F., Stroux L., Clifford G.D. Cardiotocography and beyond: A review of one-dimensional Doppler ultrasound application in fetal monitoring. Physiol. Meas. 2018;39:08TR01. doi: 10.1088/1361-6579/aad4d1. PubMed DOI PMC

Khandoker A., Kimura Y., Ito T., Sato N., Okamura K., Palaniswami M. Antepartum non-invasive evaluation of opening and closing timings of the cardiac valves in fetal cardiac cycle. Med. Biol. Eng. Comput. 2009;47:1075–1082. doi: 10.1007/s11517-009-0528-y. PubMed DOI

Lee C.S., Masek M., Lam C.P., Tan K.T. Towards Higher Accuracy and Better Noise-Tolerance for Fetal Heart Rate Monitoring using Doppler Ultrasound; Proceedings of the IEEE Region 10 Conference (TENCON); Singapore. 23–26 November 2009; pp. 1–6.

Voicu I., Menigot S., Kouame D., Girault J.M. New estimators and guidelines for better use of fetal heart rate estimators with doppler ultrasound devices. Comput. Math. Method Med. 2014;2014 doi: 10.1155/2014/784862. PubMed DOI PMC

Shakespeare S.A., Crowe J.A., Hayes-Gill B.R., Bhogal K., James D.K. The information content of Doppler ultrasound signals from the fetal heart. Med. Biol. Eng. Comput. 2001;39:619–626. doi: 10.1007/BF02345432. PubMed DOI

Wrobel J., Roj D., Jezewski J., Horoba K., Kupka T., Jezewski M. Evaluation of the robustness of fetal heart rate variability measures to low signal quality. J. Med. Imaging Health Inform. 2015;5:1311–1318. doi: 10.1166/jmihi.2015.1534. DOI

Hamelmann P., Mischi M., Kolen A.F., van Laar J.O.E.H., Vulings R., Bergmans J.W.M. Fetal Heart Rate Monitoring Implemented by Dynamic Adaptation of Transmission Power of a Flexible Ultrasound Transducer Array. Sensors. 2019;19:1195. doi: 10.3390/s19051195. PubMed DOI PMC

Vlachos M., Yu P., Castelli V. On Periodicity Detection and Structural Periodic Similarity; Proceedings of the 5th SIAM International Conference on Data Mining; Newport Beach, CA, USA. 21–23 April 2005; pp. 449–460.

Hamelmann P., Vulings R., Kolen A.F., Bergmans J.W.M., van Laar J.O.E.H., Tortoli P., Mischi M. Doppler ultrasound yechnology for fetal heart rate monitoring: A review. IEEE Trans. Ultrason. Ferroelectr. 2019;67:226–238. doi: 10.1109/TUFFC.2019.2943626. PubMed DOI

Jezewski J., Roj D., Wróbel J., Horoba K. A nowel technique for fetal heart rate estimation from Doppler ultrasound signal. Biomed. Eng. Online. 2011;10:1–17. doi: 10.1186/1475-925X-10-92. PubMed DOI PMC

Hamelmann P., Vullings R., Mischi M., Kolen A.F., Schmitt L., Bergmans J.W.M. An Extended Kalman Filter for Fetal Heart Location Estimation During Doppler-Based Heart Rate Monitoring. IEEE Trans. Instrum. Meas. 2019;68:3221–3231. doi: 10.1109/TIM.2018.2876779. PubMed DOI

Valderrama C.E., Marzbanrad F., Stroux L., Clifford G.D. Template-based Quality Assessment of the Doppler Ultrasound Signal for Fetal Monitoring. Front. Physiol. 2017;8:511. doi: 10.3389/fphys.2017.00511. PubMed DOI PMC

Divon M.Y. Autocorrelation techniques in fetal monitoring. Am. J. Obstet. Gynecol. 1985;151:2–6. doi: 10.1016/0002-9378(85)90413-2. PubMed DOI

Fukushima T., Flores C.A. Limitations of autocorrelation in fetal heart rate monitoring. Am. J. Obstet. Gynecol. 1985;153:685–692. doi: 10.1016/S0002-9378(85)80261-1. PubMed DOI

Murrills A.J., Wilmshurst T.H., Wheeler T. Antenatal measurement of beat-to-beat fetal heart rate variation: Accuracy of the Hewlett-Packard ultrasound autocorrelation technique. Fetal Physiol. Meas. 1986;6:36–44.

Taylor J., Paull C.J., Hayes-Gill B.R., Crowe J.A. Data compression of fetal Doppler ultrasound audio signals using zero-crossing analysis. Med. Eng. Phys. 1997;19:572–580. doi: 10.1016/S1350-4533(97)00005-2. PubMed DOI

Spilka J., Chudacek V., Bursa M., Zach L., Huptych M., Lhotska L., Janku P., Hruban L. Stability of Variability Features Computed from Fetal Heart Rate with Artificially Infused Missing Data. Comput. Cardiol. 2012;39:917–920.

Zhang L., Huang M.J., Wang H.J. A Novel Technique for Fetal Heart Rate Estimation Based on Ensemble Learning. Mod. Appl. Sci. 2019;13:137–147. doi: 10.5539/mas.v13n10p137. DOI

Tuck D.L. Improvement in Doppler ultrasound human foetal heart rate records by signal correlation. Med. Biol. Eng. Comput. 1982;20:357–360. doi: 10.1007/BF02442804. PubMed DOI

Romano M., Bifulco P., Ruffo M., Improta G., Clemente F., Cesarelli M. Software for computerised analysis of cardiotocographic traces. Comput. Meth. Prog. Biomed. 2016;124:121–137. doi: 10.1016/j.cmpb.2015.10.008. PubMed DOI

Romano M., Iuppariello L., Ponsiglione A.M., Improta G., Bifulco P., Cesarelli M. Frequency and Time Domain Analysis of Foetal Heart Rate Variability with Traditional Indexes: A Critical Survey. Comput. Math. Method. Med. 2016;2016:9585431. doi: 10.1155/2016/9585431. PubMed DOI PMC

Wrobel J., Kupka T., Horoba K., Matonia A., Roj D., Jezewski J. Recognition of fetal movements–automated detection from Doppler ultrasound signals compared to maternal perception. J. Med. Imaging Health Inform. 2015;5:1319–1326. doi: 10.1166/jmihi.2015.1535. DOI

Czabanski R., Jezewski J., Wrobel J., Sikora J., Jezewski M. Application of fuzzy inference system for classification of fetal heart rate tracings in relation to neonatal outcome. Gin. Pol. 2013;84:38–43. doi: 10.17772/gp/1538. PubMed DOI

Jezewski M., Czabanski R., Horoba K., Leski J.M. Clustering with pairs of prototypes to support automated assessment of the fetal state. Appl. Artif. Intell. 2016;30:572–589. doi: 10.1080/08839514.2016.1193718. DOI

Jezewski M., Leski J.M., Czabanski R. Classification based on incremental fuzzy (1+p) -means clustering. In: Gruca A., Brachman A., Kozielski S., Czachorski T., editors. Man-Machine Interactions 4. Volume 391. Springer; Cham, Germany: 2016. pp. 563–572. Advances in Intelligent Systems and Computing.

Importa G., Romano M., Ponsiglione A., Bifulco P., Faiella G., Cesarelli M. Computerized Cardiotocography: A Software to Generate Synthetic Signals. J. Health Med. Inf. 2014;5:1–6.

Mantel R., Ververs I., Colenbrander G.J., van Geijn H.P. Automated antepartum baseline FHR determination and detection of accelerations and decelerations. In: van Geijn H.P., Copray F.J.A., editors. A Critical Appraisal of Fetal Surveillance. Elsevier Science, B.V.; Amsterdam, The Netherlands: 1994. pp. 333–348.

Jezewski J., Pawlak A., Horoba K., Wrobel J., Czabanski R., Jezewski M. Selected Design Issues of the Medical Cyber-Physical System for Telemonitoring Pregnancy at Home. Microprocess. Microsyst. 2016;46:35–43. doi: 10.1016/j.micpro.2016.07.005. DOI

Wrobel J., Jezewski J., Horoba K., Pawlak A., Czabanski R., Jezewski M., Porwik P. Medical cyber-physical system for home telecare of high-risk pregnancy–design challenges and requirements. J. Med. Imaging Health Inform. 2015;5:1295–1301. doi: 10.1166/jmihi.2015.1532. DOI

Wrobel J., Matonia A., Horoba K., Jezewski J., Czabanski R., Pawlak A., Porwik P. Pregnancy telemonitoring with smart control of algorithms for signal analysis. J. Med. Imaging Health Inform. 2015;5:1302–1310. doi: 10.1166/jmihi.2015.1533. DOI

Sankhe M.S., Desai K.D., Gadam M.A. Estimate of Fetal Autonomic State by Time Spectral and Nonlinear Analysis of Fetal Heart Rate Variability. Int. J. Comput. Inf. Syst. 2016;8:312–325.

Kubo T., Inaba J., Shigemitsu S., Akatsuka T. Fetal heart variability indices and the accuracy of variability measurements. Am. J. Perinat. 1987;4:179–186. doi: 10.1055/s-2007-999768. PubMed DOI

Cesarelli M., Romano M., Bifulco P. Comparison of short term variability indexes in cardiotocographic foetal monitoring. Comput. Biol. Med. 2009;39:106–118. doi: 10.1016/j.compbiomed.2008.11.010. PubMed DOI

Goncalves H., Chaves J., Costa A., Ayres-de-Campos D., Bernardes J. Comparison of the effect of different sampling modes on computer analysis of cardiotocograms. Comput. Biol. Med. 2015;64:62–66. doi: 10.1016/j.compbiomed.2015.06.011. PubMed DOI

Goncalves H., Costa A., Ayres-de-Campos D., Costa-Santos C., Rocha A.P., Bernardes J. Comparison of real beat-to-beat signals with commercially available 4 Hz sampling on the evaluation of foetal heart rate variability, available 4 Hz sampling on the evaluation of foetal heart rate variability. Med. Biol. Eng. Comput. 2013;51:665–676. doi: 10.1007/s11517-013-1036-7. PubMed DOI

Jezewski J., Wróbel J., Horoba K. Comparison of Doppler ultrasound and direct electrocardiography acquisition techniques for quantification of fetal heart variability. IEEE Trans. Biomed. Eng. 2006;53:855–864. doi: 10.1109/TBME.2005.863945. PubMed DOI

Cesarelli M., Romano M., Bifulco P., Fedele F., Bracale M. An algorithm for the recovery of fetal heart rate series from CTG data. Comput. Biol. Med. 2007;37:663–669. doi: 10.1016/j.compbiomed.2006.06.003. PubMed DOI

Jezewski J., Kupka T., Horoba K. Extraction of Fetal Heart Rate Signal as Time Event Series from Evenly Sampled Data Acquired Using Doppler Ultrasound Technique. IEEE Trans. Biomed. Eng. 2008;55:805–810. doi: 10.1109/TBME.2007.903532. PubMed DOI

Kupka T., Matonia A., Jezewski M., Horoba K., Wrobel J., Jezewski J. Coping with limitations of fetal monitoring instrumentation to improve heart rhythm variability assessment. Biocybern. Biomed. Eng. 2020;40:388–403. doi: 10.1016/j.bbe.2019.12.005. DOI

Peters C.H.L., ten Broeke E.D., Andriessen P., Vermeulen B., Berendsen R.C.M., Wijn P.F.F., Oei S.G. Beat-to-beat detection of fetal heart rate: Doppler ultrasound cardiotocography compared to direct ECG cardiotocography in time and frequency domain. Physiol. Meas. 2004;25:585–593. doi: 10.1088/0967-3334/25/2/015. PubMed DOI

Roj D., Kupka T., Czabański R., Pander T., Jeżewski J. Improvement in fetal heart periodicity measurement using Doppler ultrasound signal; Proceedings of the 5th European Conference of the International Federation for Medical and Biological Engineering; Budapest, Hungary. 14–18 September 2011; pp. 133–136.

Al-Angari H.M., Kimura Y., Hadjileontiadis J., Khandoker A.H. A Hybrid EMD-Kurtosis Method for Estimating Fetal Heart Rate from Continuous Doppler Signals. Front. Physiol. 2017;8:641. doi: 10.3389/fphys.2017.00641. PubMed DOI PMC

van Geijn H.P. Analysis of heart rate and beat-to-beat variability: Interval difference index. Am. J. Obstet. Gynecol. 1980;138:246–252. doi: 10.1016/0002-9378(80)90242-2. PubMed DOI

Jezewski M., Czabanski R., Wrobel J., Horoba K. Analysis of Extracted Cardiotocographic Signal Reatures to Improve Automated Prediction of Fetal Outcome. Biocybern. Biomed. Eng. 2010;30:29–47.

Frigo G., Giorgi G. Comparative Evaluation of On-Line Missing Data Regression Techniques in Intrapartum FHR Measurements; Proceedings of the IEEE IMTC Conference; Torino, Italy. 22–25 May 2017; DOI

Lauersen N.H., Hochberg H.M., George M.E.D. Evaluation of the accuracy of a new ultrasonic fetal heart rate monitor. Am. J. Obstet. Gynecol. 1976;125:1125–1135. doi: 10.1016/0002-9378(76)90819-X. PubMed DOI

Dawes G.S., Visser G.H.A., Goodman J.D.S., Redman C.W.G. Numerical analysis of the human fetal heart rate: The quality of ultrasound records. Am. J. Obstet. Gynecol. 1981;141:43–52. doi: 10.1016/0002-9378(81)90673-6. PubMed DOI

Lawson G.W., Dawes G.S., Redman C.W.G. A comparison of two fetal heart rate ultrasound detector systems. Am. J. Obstet. Gynecol. 1982;143:840–842. doi: 10.1016/0002-9378(82)90021-7. PubMed DOI

Lawson G.W., Belcher R., Dawes G.S., Redman C.W.G. A comparison of ultrasound (with autocorrelation) and direct electrocardiogram fetal heart rate detector systems. Am. J. Obstet. Gynecol. 1983;147:721–722. doi: 10.1016/0002-9378(83)90460-X. PubMed DOI

A comparative study of single-channel signal processing methods in fetal phonocardiography