Fetal heart rate monitoring: from Doppler to computerized analysis

Feasibility of a mobile cardiotocogram device for fetal heart rate self-monitoring in low-risk singleton pregnant women

AIM

This study aimed to clarify the feasibility of a mobile cardiotocogram (CTG) device for self-monitoring fetal heart rate (FHR) in low-risk singleton pregnant women.

METHODS

This study was conducted at six university hospitals and seven maternity clinics in Japan. Using a mobile cardiotocogram device (iCTG, Melody International Ltd., Kagawa, Japan), participants of more than 34 gestational weeks measured the FHR by themselves at least once a week until hospitalization for delivery. We evaluated the acquisition rate of evaluable FHR recordings and the frequency of abnormal FHR patterns according to the CTG classification system of the Japan Society of Obstetrics and Gynecology (JSOG). The participants also underwent a questionnaire survey after delivery to evaluate their satisfaction level of self-monitoring FHR using the mobile CTG device.

RESULTS

A total of 1278 FHR recordings from 101 women were analyzed. Among them, 1276 (99.8%) were readable for more than 10 min continuously, and the median percentage of the total readable period in each recording was 98.9% (range, 51.4-100). According to the JSOG classification system, 1245 (97.6%), 9 (0.7%), 18 (1.4%), and four (0.3%) FHR patterns were classified as levels 1, 2, 3, and 4, respectively. The questionnaire survey revealed high participant satisfaction with FHR self-monitoring using the iCTG.

CONCLUSION

The mobile CTG device is a feasible tool for self-monitoring FHR, with a high participant satisfaction level.

Intrapartum fetal monitoring and perinatal risk factors of neonatal hypoxic-ischemic encephalopathy

BACKGROUND

Neonatal hypoxic-ischemic encephalopathy (HIE) in term infants, is a major cause of neonatal mortality and severe neurologic disability.

OBJECTIVES

To identify in labor fetal monitoring characteristic patterns and perinatal factors associated with neonatal HIE.

STUDY DESIGN

Single-center retrospective case-control study between 2010 and 2017. Cases clinically diagnosed with neonatal HIE treated by therapeutic hypothermia according to strict criteria (HIE-TH) were compared to a group of neonates born in the same period, gestational age-matched diagnosed with fetal distress according to fetal monitoring interpretation that was followed by prompt delivery, without subsequent HIE or therapeutic hypothermia (No-HIE). The primary outcome of the study was the electronic fetal monitoring (EFM) pattern during 60 min prior to delivery; the secondary outcome was the identification of perinatal associated factors.

RESULTS

54 neonates with HIE were treated by therapeutic hypothermia. EFM parameters most predictive of HIE-TH were indeterminate baseline heart rate OR = 47.297, 95% (8.17-273.76) p < 0.001, bradycardia OR = 15.997 95% (4.18-61.18) p < 0.001, low variability OR = 10.224, 95% (2.71-38.45) p < 0.001, higher baseline of the fetal heart rate calculated for each increment of 1 BPM OR = 1.0547, 95% (1.001-1.116) p = 0.047. Rupture of a previous uterine cesarean scar and placental abruption were characteristic of the HIE-TH group 14.8% vs. 1% p < 0.05; and 16.7% vs. 6% p < 0.05, respectively. Adverse neonatal outcomes also differed significantly: HIE-TH had a higher rate of neonatal seizures 46.2% vs. 0% p < 0.001 and mortality 7.7% vs. 0% p < 0.001.

CONCLUSIONS

Characteristic fetal monitoring pattern prior to delivery together with acute obstetric emergency events are associated with neonatal HIE, neurological morbidity, and mortality.

Model based estimation of QT intervals in non-invasive fetal ECG signals

The end timing of T waves in fetal electrocardiogram (fECG) is important for the evaluation of ST and QT intervals which are vital markers to assess cardiac repolarization patterns. Monitoring malignant fetal arrhythmias in utero is fundamental to care in congenital heart anomalies preventing perinatal death. Currently, reliable detection of end of T waves is possible only by using fetal scalp ECG (fsECG) and fetal magnetocardiography (fMCG). fMCG is expensive and less accessible and fsECG is an invasive technique available only during intrapartum period. Another safer and affordable alternative is the non-invasive fECG (nfECG) which can provide similar assessment provided by fsECG and fMECG but with less accuracy (not beat by beat). Detection of T waves using nfECG is challenging because of their low amplitudes and high noise. In this study, a novel model-based method that estimates the end of T waves in nfECG signals is proposed. The repolarization phase has been modeled as the discharging phase of a capacitor. To test the model, fECG signals were collected from 58 pregnant women (age: (34 ± 6) years old) bearing normal and abnormal fetuses with gestational age (GA) 20-41 weeks. QT and QTc intervals have been calculated to test the level of agreement between the model-based and reference values (fsECG and Doppler Ultrasound (DUS) signals) in normal subjects. The results of the test showed high agreement between model-based and reference values (difference < 5%), which implies that the proposed model could be an alternative method to detect the end of T waves in nfECG signals.

[Optimal template selecting combined with non-liner template matching for Doppler fetal heart rate extraction]

The ultrasound Doppler fetal heart rate measurement is the gold standard of fetal heart rate counting. However, the existing fetal heart rate extraction algorithms are not designed specifically to suppress the high maternal interference during the second stage of labor, and false detection occurrences are common during labor. With this background, a method combining time-frequency frame template library optimal selecting and non-linear template matching is proposed. The method contributes a template library, and the optimal template can be selected to match the signal frame. After the short-time Fourier transform of the signal, the difference between the signal and the template is optimized by leaky rectified linear unit (LReLU) function frame by frame. The heart rate was calculated from the peak of the matching curve and the heart rate was calculated. By comparing the proposed method with the autocorrelation method, the results show that the detection accuracy of the proposed method is improved by 20% on average, and the non-linear template matching of 23% samples is at least 50% higher than the autocorrelation method. This paper designs the algorithm by analyzing the characteristics of the interference and signal mixing. We hope that this paper will provide a new idea for fetal heart rate extraction which not only focuses on the original signal.

Cardiotocography and beyond: a review of one-dimensional Doppler ultrasound application in fetal monitoring

One-dimensional Doppler ultrasound (1D-DUS) provides a low-cost and simple method for acquiring a rich signal for use in cardiovascular screening. However, despite the use of 1D-DUS in cardiotocography (CTG) for decades, there are still challenges that limit the effectiveness of its users in reducing fetal and neonatal morbidities and mortalities. This is partly due to the noisy, transient, complex and nonstationary nature of the 1D-DUS signals. Current challenges also include lack of efficient signal quality metrics, insufficient signal processing techniques for extraction of fetal heart rate and other vital parameters with adequate temporal resolution, and lack of appropriate clinical decision support for CTG and Doppler interpretation. Moreover, the almost complete lack of open research in both hardware and software in this field, as well as commercial pressures to market the much more expensive and difficult to use Doppler imaging devices, has hampered innovation. This paper reviews the basics of fetal cardiac function, 1D-DUS signal generation and processing, its application in fetal monitoring and assessment of fetal development and wellbeing. It also provides recommendations for future development of signal processing and modeling approaches, to improve the application of 1D-DUS in fetal monitoring, as well as the need for annotated open databases.

Fetal Cardiac Doppler Signal Processing Techniques: Challenges and Future Research Directions

The fetal Doppler Ultrasound (DUS) is commonly used for monitoring fetal heart rate and can also be used for identifying the event timings of fetal cardiac valve motions. In early-stage fetuses, the detected Doppler signal suffers from noise and signal loss due to the fetal movements and changing fetal location during the measurement procedure. The fetal cardiac intervals, which can be estimated by measuring the fetal cardiac event timings, are the most important markers of fetal development and well-being. To advance DUS-based fetal monitoring methods, several powerful and well-advanced signal processing and machine learning methods have recently been developed. This review provides an overview of the existing techniques used in fetal cardiac activity monitoring and a comprehensive survey on fetal cardiac Doppler signal processing frameworks. The review is structured with a focus on their shortcomings and advantages, which helps in understanding fetal Doppler cardiogram signal processing methods and the related Doppler signal analysis procedures by providing valuable clinical information. Finally, a set of recommendations are suggested for future research directions and the use of fetal cardiac Doppler signal analysis, processing, and modeling to address the underlying challenges.