Antenatal Noninvasive Fetal Electrocardiography: A Literature Review

Figures

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  Figure 1. Timeline of major developments in healthcare and fetal monitoring. Icons from flaticon.com. Adapted from Pregnancy in the time of COVID-19: towards Fetal monitoring 4.0. BMC Pregnancy Childbirth 2023;23(1):33. doi: 10.1186/s12884-023-05349-3. © 2023 is licensed under CC BY 4.0. To view a copy of this license, visit https://creativecommons.org/licenses/by/4.0/

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  Figure 2. Regulation of heart rate variability. The heart has its intrinsic neurological system. The parasympathetic (vagal nerve) and sympathetic nervous system influence heart rate variability. Chemoreceptors, baroreceptors, proprioceptors, and the cerebral cortex govern this interaction. BP: Blood pressure; PNS: Parasympathetic nervous system; SNS: Sympathetic nervous system; SA node: Sinoatrial node.

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  Figure 3. Example of computerized CTG from Huntleigh Fetal Care. A Each minute is divided into 16 epochs of 3.75 ms each. Patient consent was obtained for reproducing this image. The FHR is averaged over each epoch and displayed in bpm. The red rectangle highlights the division of each minute into epochs. The yellow rectangle indicates the first analysis at 10 minutes, marking the minimum monitoring period. The blue rectangle shows that the recording can be stopped once criteria are met, here at 40 minutes. Green arrows denote accelerations, while orange arrows indicate uterine contractions. The light blue solid rectangle marks episodes of low variation, and the dark blue solid rectangle marks episodes of high variation. B The Dawes-Redman report displays variables and their units in the left column, with corresponding results in the right column (asterisk indicates analysis only includes maternally reported movements). CTG: Cardiotocography; FHR: Fetal heart rate; bpm: Beats per minute; FHR1: Fetal heart rate 1 (singleton); MET: Criteria met (appears as ‘NOT MET’ if criteria are not met); STV: Short-term variation; ms: Milliseconds; Toco %: Tocodynamometer.

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  Figure 4. Kalman Filtering. A The abdominal ECG displaying both maternal and fetal ECG signals. B The maternal ECG component isolated from the abdominal ECG. C The residual signal after removing the maternal ECG, representing the fetal ECG with very low amplitude compared to the maternal ECG. aECG: Abdominal electrocardiogram; mECG: Maternal electrocardiogram; ECG: Electrocardiogram. Adapted from A review of signal processing techniques for non-invasive fetal electrocardiography. IEEE Rev Biomed Eng 2020;13:51–73. doi: 10.1109/RBME.2019.2938061. © 2020 is licensed under CC BY 4.0. To view a copy of this license, visit https://creativecommons.org/licenses/by/4.0/

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  Figure 5. The scatter plot showing the correlation of eSTV (NIFECG STV) obtained through NIFECG using the Femom monitor (filtered) and cSTV obtained from computerized CTG using the Huntleigh machine. F-filtered: Fully filtered; CTG: Cardiotocography; cSTV: computerized short-term variation; ms: Milliseconds; NIFECG: Noninvasive fetal electrocardiogram; STV: Short-term variation. Adapted from Correlation of short-term variation derived from novel ambulatory fetal electrocardiography monitor with computerized cardiotocography by B. Liu, B. Thilaganathan, A. Bhide. © 2023 is licensed under CC BY 4.0. To view a copy of this license, visit https://creativecommons.org/licenses/by/4.0/