Analysis Of Fetal Heart Rate Variability Research Articles

STUDY AND ANALYSIS OF FETAL HEART RATE MONITORING SYSTEM

Analysis of FHR variability, together with uterine muscle contractions and fetal movement activity, subject to cardiotocographic monitoring, currently play a fundamental role in fetal assessment. The strength of cardiotocography lies in that normal ranges of the results of the FHR signal analysis almost always (>95%) confirm fetal wellbeing. Unfortunately, questionable or abnormal signal features may indicate both fetal distress and its absence. The classic fetal heart rate variability analysis consists in determining the FHR baseline and then in identifying bradycardia/tachycardia, acceleration/deceleration patterns as well as the type and amplitude of oscillations. A more advanced FHR analysis is aimed at evaluating instantaneous FHR variability, especially with beat-to-beat approach, which is very important in fetal condition assessment. The most common technique of recording the FHR signal is the Doppler ultrasound method, which makes it difficult to correctly estimate the instantaneous heart rate variability because the measurements are averaged. On the other hand, instantaneous heart rate variability plays a crucial role in the diagnosis of fetal condition [1]. The increased interest in monitoring the fetal cardiac bioelectrical activity is due to the fact that the analysis of the fetal electrocardiogram ensures high efficiency and accuracy of the heart rate measurement even on a beat-to-beat level. The first fetal electrocardiogram was recorded as early as in the 1960-ies by means of a special spiral electrode enabling direct signal registration from a fetal head. Due to the way the electrode is placed, its use is limited only to the advanced labour stage [1]..

Uterine activity modifies the response of the fetal autonomic nervous system at preterm active labor.

The autonomic nervous system of preterm fetuses has a different level of maturity than term fetuses. Thus, their autonomic response to transient hypoxemia caused by uterine contractions in labor may differ. This study aims to compare the behavior of the fetal autonomic response to uterine contractions between preterm and term active labor using a novel time-frequency analysis of fetal heart rate variability (FHRV). We performed a case-control study using fetal R-R and uterine activity time series obtained by abdominal electrical recordings from 18 women in active preterm labor (32-36 weeks of gestation) and 19 in active term labor (39-40 weeks of gestation). We analyzed 20 minutes of the fetal R-R time series by applying a Continuous Wavelet Transform (CWT) to obtain frequency (HF, 0.2-1Hz; LF, 0.05-0.2Hz) and time-frequency (Flux0, Flux90, and Flux45) domain features. Time domain FHRV features (SDNN, RMSSD, meanNN) were also calculated. In addition, ultra-short FHRV analysis was performed by segmenting the fetal R-R time series according to episodes of the uterine contraction and quiescent periods. No significant differences between preterm and term labor were found for FHRV features when calculated over 20 minutes. However, we found significant differences when segmenting between uterine contraction and quiescent periods. In the preterm group, the LF, Flux0, and Flux45 were higher during the average contraction episode compared with the average quiescent period (p<0.01), while in term fetuses, vagally mediated FHRV features (HF and RMSSD) were higher during the average contraction episode (p<0.05). The meanNN was lower during the strongest contraction in preterm fetuses compared to their consecutive quiescent period (p=0.008). The average autonomic response to contractions in preterm fetuses shows sympathetic predominance, while term fetuses respond through parasympathetic activity. Comparison between groups during the strongest contraction showed a diminished fetal autonomic response in the preterm group. Thus, separating contraction and quiescent periods during labor allows for identifying differences in the autonomic nervous system cardiac regulation between preterm and term fetuses.

Classification of FHR Signals Based on Morphological Features

Electronic fetal monitoring is a non-invasive procedure employed to assess the fetal health before and during labor. In this method, fetal heart rate (FHR) is measured by placing electrodes on the mother’s abdomen. The corresponding FHR signal is recorded on the graph called Cardiotocograph (CTG). During intrapartum, CTG records the changes in FHR in response to uterine contractions and helps in identifying the symptoms of fetal distress that may occur during the labor. In the present study, an algorithm is developed to calculate the features of fetal heart rate variability (FHRV). According to the RCOG guidelines, these features can be used to classify the subjects with normal, suspicious, and abnormal FHRV. Correctly interpreting the FHR variability enables early detection of fetal distress, thereby reducing fetal mortality rate. FHRV analysis also helps the obstetricians in efficient clinical decision making and avoiding unnecessary caesarean sections.

Recording and quantifying fetal magnetocardiography signals using a flexible array of optically-pumped magnetometers

Objective: Fetal magnetocardiography (fMCG) is a non-invasive biomagnetic technique that provides detailed beat-to-beat fetal heart rate analysis, both in normal rhythm as well as in fetal arrhythmias. New cryogenic-free sensors called optically pumped magnetometers (OPMs) have emerged as a less expensive and more geometrically flexible alternative to traditional Superconducting Quantum Interference Device (SQUID) technology for performing fMCG. The objective of the study was to show the ability of OPMs to record fMCG using flexible geometry while seeking to preserve signal quality, and to quantify fetal heart rate variability (FHRV). Approach: Biomagnetic measurements were performed with OPMs in 24 healthy pregnant women with uncomplicated singleton pregnancies between 28 and 38 weeks gestation (GA). A total of 96 recordings were analyzed from OPM data that was collected using sensors placed in two different maternal configurations over the abdomen. The fMCG signals were extracted and the quality of the recordings were quantified by peak amplitudes and signal-to-noise ratio (SNR). R peaks were used to perform both time and frequency domain FHRV analysis. FHRV measures obtained from OPMs were compared descriptively to the same measures obtained from GA-matched existing SQUID data. Main results: The fMCG derived from OPMs were observed in 21 of the 24 participants. Higher detection rates (85%) of fMCG signals were observed in the data sets recorded at GA >32 weeks. Peak amplitudes and SNR values were similar between two maternal configurations, but peak amplitudes were significantly higher (p = 0.013) in late GA compared to early GA. FHRV indicators were successfully extracted and their values overlapped substantially with those obtained from SQUID recordings. Significance: Taking advantage of the geometric flexibility of the OPMs, we have demonstrated their ability to record and quantify fMCG in different maternal positions as opposed to rigid SQUID configurations.

Influence of averaged fetal heart rate in heart rate variability analysis.

In high-income countries, fetal hypoxia affects 3 to 8 newborns per 1000 live births with subsequent moderate or severe Hypoxic-Ischemic Encephalopathy (HIE) in 0.5 to 1 per 1000 live births. Visual interpretation of FHR signal issued from a Doppler ultrasound cardiotocography is the gold standard to monitor fetal condition. Unfortunately, its analysis presents a high rate of inter-observer variability and a low specificity to predict poor neonatal outcomes. Under hypoxia, the fetus develops several adaptive mechanisms regulated by the autonomic nervous system inducing changes in the fetal heart rate variability. Though fetal heart rate variability methods demonstrated abilities to predict perinatal asphyxia, most of the Doppler ultrasound technologies used in clinical practice do not provide sufficiently accurate fetal heart rate signals for heart rate variability analysis. Indeed, Doppler ultrasound cardiotocography usually provides fetal heart rate values averaged over 2 or 3 beats which can constitute a limitation for spectral analysis. We developed a fetal heart rate variability analysis method: the Fetal Stress Index (FSI). The objective of this study was to investigate the influence of averaged fetal heart rate on this new index in order to check the feasibility of computing the FSI from the signal issued from Doppler ultrasound cardiotocography.

Parasympathetic tone variations according to umbilical cord pH at birth: a computerized fetal heart rate variability analysis.

Non-reassuring fetal heart rate tracings reflect an imbalance between the parasympathetic and sympathetic nervous systems. In this situation, fetal asphyxia can be suspected and may be confirmed by metabolic measurements at birth like low pH or high base deficit values. The objective of this study was to determine whether fetal asphyxia during labor is related to parasympathetic nervous system activity. This is a retrospective study of a database collected in 5 centers. Two hundred and ninety-nine fetal heart rate tracings collected during labor were analyzed. Autonomic nervous system, especially the parasympathetic nervous system, was analyzed using an original index: the FSI (Fetal Stress Index). The FSI is a parasympathetic activity evaluation based on fetal heart rate variability analysis. Infants were grouped based on normal or low pH value at birth. FSI was measured during the last 30min of labor before birth and compared between groups. The minimum value of the FSI during the last 30min before delivery was significantly lower in the group with the lower umbilical cord arterial pH value. In this pilot study during labor, FSI was lower in the group of infants with low arterial pH at birth.

Using uterine activity to improve fetal heart rate variability analysis for detection of asphyxia during labor

During labor, uterine contractions can cause temporary oxygen deficiency for the fetus. In case of severe and prolonged oxygen deficiency this can lead to asphyxia. The currently used technique for detection of asphyxia, cardiotocography (CTG), suffers from a low specificity. Recent studies suggest that analysis of fetal heart rate variability (HRV) in addition to CTG can provide information on fetal distress. However, interpretation of fetal HRV during labor is difficult due to the influence of uterine contractions on fetal HRV. The aim of this study is therefore to investigate whether HRV features differ during contraction and rest periods, and whether these differences can improve the detection of asphyxia. To this end, a case-control study was performed, using 14 cases with asphyxia that were matched with 14 healthy fetuses. We did not find significant differences for individual HRV features when calculated over the fetal heart rate without separating contractions and rest periods (p > 0.30 for all HRV features). Separating contractions from rest periods did result in a significant difference. In particular the ratio between HRV features calculated during and outside contractions can improve discrimination between fetuses with and without asphyxia (p < 0.04 for three out of four ratio HRV features that were studied in this paper).

Correlating multidimensional fetal heart rate variability analysis with acid-base balance at birth

Fetal monitoring during labour currently fails to accurately detect acidemia. We developed a method to assess the multidimensional properties of fetal heart rate variability (fHRV) from trans-abdominal fetal electrocardiogram (fECG) during labour. We aimed to assess this novel bioinformatics approach for correlation between fHRV and neonatal pH or base excess (BE) at birth.We enrolled a prospective pilot cohort of uncomplicated singleton pregnancies at 38–42 weeks’ gestation in Milan, Italy, and Liverpool, UK. Fetal monitoring was performed by standard cardiotocography. Simultaneously, with fECG (high sampling frequency) was recorded. To ensure clinician blinding, fECG information was not displayed. Data from the last 60 min preceding onset of second-stage labour were analyzed using clinically validated continuous individualized multiorgan variability analysis (CIMVA) software in 5 min overlapping windows. CIMVA allows simultaneous calculation of 101 fHRV measures across five fHRV signal analysis domains. We validated our mathematical prediction model internally with 80:20 cross-validation split, comparing results to cord pH and BE at birth.The cohort consisted of 60 women with neonatal pH values at birth ranging from 7.44 to 6.99 and BE from −0.3 to −18.7 mmol L−1. Our model predicted pH from 30 fHRV measures (R2 = 0.90, P < 0.001) and BE from 21 fHRV measures (R2 = 0.77, P < 0.001).Novel bioinformatics approach (CIMVA) applied to fHRV derived from trans-abdominal fECG during labor correlated well with acid-base balance at birth. Further refinement and validation in larger cohorts are needed. These new measurements of fHRV might offer a new opportunity to predict fetal acid-base balance at birth.

Classification System for Fetal Heart Rate Variability Measures Based on Cardiotocographies

The Fetal Heart Rate interpretation based on Cardiotocographies (CTG) is the most common practice of obstetrician medical staffs. Computerized CTG Systems are used with the aim to reduce subjective aspects of these diagnostics. The Fetal Heart Rate Variability (FHRV) analysis using the CTG signal is an unusual approach. This work proposes a FHRV analysis based on the evaluation of time domain parameters (statistic measures); frequency domain parameters; and the short and long term variability obtained from the Poincare plot. A normal distribution is presumed for each parameter and a normality criterion is proposed. Specific and overall classifications are proposed to help improve the fetal conditions interpretation, expanding the conventional FHR analysis.

Short term variability of fetal heart rate during pregnancies complicated by hypertension.

The clinical significance of the differential index (DI), which describes the short term variability of fetal heart rate (FHR), in fetal surveillance was assessed in 202 hypertensive pregnancies. The analyses of FHR variability were made by a microprocessor-based on-line method using the abdominal fetal electrocardiogram as a triggering signal. The analysis was successful in 258 out of 323 trials (80%). Five perinatal deaths (2.5%) occurred in the whole series. Fetal distress developed in 47 out of 137 patients who had a successful FHR analysis within 1 week of delivery. The sensitivity of the antepartum DI in predicting fetal distress in labour was 46%, predictive value was 88% and specificity 97%. The risk of intrapartum fetal distress after a pathological DI was 4 times that after a normal DI (relative risk), which is highly significant.

Midtrimester fetal heart rate variability and maternal hemodynamics in association with smoking

Maternal heart rate (MHR), blood pressure (BP), the differential index (DI) describing the short-term component of fetal heart rate (FHR) variability, and the interval index (II) describing the long-term component were measured in eight subjects in the midtrimester before, during, and after the mothers smoked a standard cigarette. The analyses of FHR variability were performed by an “on-line” method with an abdominal fetal electrocardiogram used as a triggering signal and with a sample time of 1 minute. An increase of MHR, FHR, and BP with a concomitant decrease of II was observed. Unlike our findings regarding the third trimester, no significant change of DI was observed. A correlation analysis revealed fetomaternal hemodynamic relationships different from those in the third trimester: There was a negative correlation between DI and FHR (p < 0.01) and between DI and MHR (p < 0.01). There was a positive correlation between FHR and MHR (p < 0.001). Unlike our findings regarding the third trimester, no correlation was found between DI and BP or between II and MHR. We suggest that the midtrimester fetus shows the narcotic effect (decrease of II) of one cigarette, as does the term fetus, but fails to show the hypoxic effect (decrease of DI), which has been observed in the term fetus.

Antepartal analysis of fetal heart rate variability by abdominal electrocardiography.

The success rate of some methodological factors influencing the antepartal analysis of fetal heart rate variability (FHRV) by abdominal electrocardiography (aFECG) were studied in 80 normal and 554 high risk pregnancies. The success rate of FHRV analysis was found to be dependent on the gestational age with virtually 100% success at 22 to 25 weeks and at 40 to 41 weeks of gestation. The lowest rate of success, 50% was found around the 30th week of gestation (Fig. 1). The fifteen-degree lateral tilt and the supine position of the mother were found to be equal respecting the success rate and the test results, while the 90-degree lateral tilt was found to be less favorable for the analysis. FHRV analysis succeeded more often with electrode paste than it did with tap water moistening or with dry electrodes. The rejection limit of maximum interval differences in FHRV analysis was found to be an important factor influencing the test results. The variability indices should be compared only if they have been measured with the same rejection logic. Differential index, of short-term variability, can be measured from short samples of aFECG, having a good correlation between DIs measured using 1-minute, 5-minute and 20-minute samples (Figs. 3, 4). On the other hand, interval index measuring the long-term variability should be measured using longer samples of aFECG.

Short-term variability of fetal heart rate during pregnancies with normal and insufficient placental function

The differential index (DI) describing the short-term component of the fetal heart rate (FHR) was measured serially in 65 fetuses during normal pregnancies, in 68 fetuses with suspected intrauterine growth retardation (IUGR), and in 84 fetuses with suspected postmaturity. The analyses of FHR variability were made by a microprocessor-based “on-line” method with the use of the abdominal fetal electrocardiogram (aFECG) in the statistical calculation of the interval differences. The analysis of FHR variability was successful 463 of 581 times (80%) in the reference group, 73 of 89 times (82%) in the group with suspected IUGR, and 121 of 127 times (95%) in the group with suspected postmaturity. There was no fetal distress in the reference group, but fetal distress did occur in 24 (35%) of the IUGR fetuses and in 13 (15%) of the postmature fetuses. The first percentile limit of DIs in the normal group was used as the normal limit of DI for fetuses with IUGR. In the postmature group the cutoff level of DI was set at 3.5. The sensitivity of DI in predicting fetal distress was 64% in the group with suspected IUGR and 54% in the group with suspected postmaturity. The predictive values of DI were 80% and 58%, respectively. The risk ratios of abnormal and normal DIs were 3.6 in suspected IUGR and 6.8 in suspected postmaturity. Hence, DI seems to be a sensitive and reliable indicator of developing fetal distress in suspected IUGR and postmaturity. The fairly high failure rate of aFECG at the onset of the third trimester of pregnancy limits the practical value of FHR analysis.

On-line quantification of fetal heart rate variability.

An on-line methods for quantification of fetal heart rate variability (FHRV) from fetal electrocardiography (FECG) is presented. A CMOS microprocessor system with a 2k read-only-memory and a 4k random-access-memory is constructed. The processor is connected to a commercial cardiotocograph, and it calculates the interval index (II) measuring the long-term variability and the differential index (DI) measuring the short-term variability of FHR. The accuracy of the system was tested by calculating the FHRV indices from simultaneously recorded direct FECG and abdominal FECG. The correlation between the results of these two methods was good. II and DI were calculated serially for 34 fetuses during normal pregnancies. The FHRV analysis succeeded in 80-100 percent of patients from the 20th until the 27th week of gestation and again from the 35th week until term. The method was less successful, 35-70 percent, between gestational weeks 28 and 34. On average, II and DI grew as the gestation advanced. II had a greater scatter than DI and it was considered to measure mainly the fetal arousal level. DI on the other hand was not below three after the 30th week of gestation. DI may become a new marker of fetal status also in antepartum fetal surveillance.