Randomised controlled trial of intrapartum fetal heart rate monitoring.

OBJECTIVE--To compare effectiveness of different methods of monitoring intrapartum fetal heart rate. DESIGN--Prospective randomised controlled trial. SETTING--Referral maternity hospital, Harare, Zimbabwe. SUBJECTS--1255 women who were 37 weeks or more pregnant with singleton cephalic presentation and normal fetal heart rate before entry into study. INTERVENTIONS--Intermittent monitoring of fetal heart rate by electronic monitoring, Doppler ultrasound, use of Pinard stethoscope by a research midwife, or routine use of Pinard stethoscope by attending midwife. MAIN OUTCOME MEASURES--Abnormal fetal heart rate patterns, need for operative delivery for fetal distress, neonatal mortality, Apgar scores, admission to neonatal unit, neonatal seizures, and hypoxic ischaemic encephalopathy. RESULTS--Abnormalities in fetal heart rate were detected in 54% (172/318) of the electronic monitoring group, 32% (100/312) of the ultrasonography group, 15% (47/310) of the Pinard stethoscope group, and 9% (28/315) of the routine monitoring group. Caesarean sections were performed for 28% (89%), 24% (76), 10% (32), and 15% (46) of the four groups respectively. Neonatal outcome was best in the ultrasonography group: hypoxic ischaemic encephalopathy occurred in two, one, seven, and 10 cases in the four groups respectively; neonatal seizures occurred only in the last two groups (six and nine cases respectively); and deaths occurred in eight, two, five, and nine cases respectively. CONCLUSIONS--Abnormalities in fetal heart rate were more reliably detected by Doppler ultrasonography than with Pinard stethoscope, and its use resulted in good perinatal outcome. The use of relatively cheap ultrasound monitors should be further evaluated and promoted in obstetric units caring for high risk pregnancies in developing countries with scarce resources.     

Experience with fetal monitoring in a university teaching hospital.

Fetal monitoring during labour may be expected to decrease perinatal losses and the number of infants born with brain damage. In a prospective study of intrapartum fetal monitoring in selected high-risk pregnancies in a Winnipeg hospital the monitoring rate was 26.5% and the cesarean section rate in the monitored group was 22.0%. The fetal outcome in the monitored group was better than in the unmonitored group. The establishment of a fetal intensive care unit is believed to be strongly desirable in improving fetal surveillance during labour. Fetal monitors should be stationed in the delivery room as well as in the first-stage room.     

Monitoring fetal electrocortical activity during labour for predicting worsening acidemia: a prospective study in the ovine fetus near term

Background

Severe fetal acidemia during labour with arterial pH below 7.00 is associated with increased risk of hypoxic-ischemic brain injury. Electronic fetal heart rate (FHR) monitoring, the mainstay of intrapartum surveillance, has poor specificity for detecting fetal acidemia. We studied brain electrical activity measured with electrocorticogram (ECOG) in the near term ovine fetus subjected to repetitive umbilical cord occlusions (UCO) inducing FHR decelerations, as might be seen in human labour, to delineate the time-course for ECOG changes with worsening acidemia and thereby assess the potential clinical utility of fetal ECOG.

Methodology/Principal Findings

Ten chronically catheterized fetal sheep were studied through a series of mild, moderate and severe UCO until the arterial pH was below 7.00. At a pH of 7.24±0.04, 52±13 min prior to the pH dropping <7.00, spectral edge frequency (SEF) increased to 23±2 Hz from 3±1 Hz during each FHR deceleration (p<0.001) and was correlated to decreases in FHR and in fetal arterial blood pressure during each FHR deceleration (p<0.001).

Conclusions/Significance

The UCO-related changes in ECOG occurred in advance of the pH decreasing below 7.00. These ECOG changes may be a protective mechanism suppressing non-essential energy needs when oxygen supply to the fetal brain is decreased acutely. By detecting such “adaptive brain shutdown,” the need for delivery in high risk pregnant patients may be more accurately predicted than with FHR monitoring alone. Therefore, monitoring fetal electroencephalogram (EEG, the human equivalent of ECOG) during human labour may be a useful adjunct to FHR monitoring.     

Effectiveness of intrapartum fetal surveillance to improve maternal and neonatal outcomes: a systematic review and network meta-analysis

BACKGROUND:Cesarean delivery is the most common surgical procedure worldwide. Intrapartum fetal surveillance is routinely offered to improve neonatal outcomes, but the effects of different methods on the risk of emergency cesarean deliveries remains uncertain. We conducted a systematic review and network meta-analysis to evaluate the effectiveness of different types of fetal surveillance.METHODS:We searched MEDLINE, Embase and CENTRAL until June 1, 2020, for randomized trials evaluating any intrapartum fetal surveillance method. We performed a network meta-analysis within a frequentist framework. We assessed the quality and network inconsistency of trials. We reported primarily on intrapartum emergency cesarean deliveries and other secondary maternal and neonatal outcomes using risk ratios (RRs) and 95% confidence intervals (CIs).RESULTS:We included 33 trials (118 863 patients) evaluating intermittent auscultation with Pinard stethoscope/handheld Doppler (IA), cardiotocography (CTG), computerized cardiotocography (cCTG), CTG with fetal scalp lactate (CTG-lactate), CTG with fetal scalp pH analysis (CTG-FBS), CTG with fetal pulse oximetry (FPO-CTG), CTG with fetal heart electrocardiogram (CTG-STAN) and their combinations. Intermittent auscultation reduced the risk of emergency cesarean deliveries compared with other types of surveillance (IA v. CTG: RR 0.83, 95% CI 0.72–0.97; IA v. CTG-FBS: RR 0.71, 95% CI 0.63–0.80; IA v.CTG-lactate: RR 0.77, 95% CI 0.64–0.92; IA v. FPO-CTG: RR 0.75, 95% CI 0.65–0.87; IA v.FPO-CTG-FBS: RR 0.81, 95% CI 0.67–0.99; cCTG-FBS v. IA: RR 1.21, 95% CI 1.04–1.42), except STAN-CTG-FBS (RR 1.17, 95% CI 0.98–1.40). There was a similar reduction observed for emergency cesarean deliveries for fetal distress. None of the evaluated methods was associated with a reduced risk of neonatal acidemia, neonatal unit admissions, Apgar scores or perinatal death.INTERPRETATION:Compared with other types of fetal surveillance, intermittent auscultation seems to reduce emergency cesarean deliveries in labour without increasing adverse neonatal and maternal outcomes.

Cesarean delivery is the most common surgical procedure worldwide, performed to expedite delivery and avoid neonatal complications. Fetal surveillance is routinely offered to patients in labour to reduce the risk of adverse neonatal outcomes, as well as the risk of unnecessary emergency cesarean deliveries and other maternal interventions. Fetal surveillance aims to detect intrapartum hypoxia from acute or subacute adverse events in labour requiring medical intervention and to reduce the risk of serious complications such as neonatal cerebral palsy, hypoxic–ischemic encephalopathy or stillbirth.Monitoring the fetal heart rate to detect intrapartum hypoxia using simple surveillance techniques, such as the Pinard stethoscope, has been practised for decades.¹ Over the last 50 years, several newer surveillance methods have been evaluated, with varied uptake in practice.² Cardiotocography (CTG) remains the most common surveillance method used in high-risk pregnancies.³ However, given its limited accuracy, many researchers have evaluated its use in combination with other surveillance methods, such as fetal heart electrocardiogram (STAN), fetal scalp pH analysis (FBS) or fetal pulse oximetry (FPO), and with computer-aided decision models (cCTG) to improve its diagnostic value.^4–6 Despite extensive investment in clinical research, the overall effectiveness of such methods in improving maternal and neonatal outcomes remains debatable as stillbirth rates have plateaued worldwide, while cesarean delivery rates continue to rise.^7,8Existing meta-analyses evaluating different intrapartum fetal surveillance methods remain limited to head-to-head comparisons of monitoring techniques, without a comprehensive assessment of their effectiveness in improving maternal and neonatal pregnancy outcomes.^4,9–13 We conducted a systematic review of randomized trials and a network meta-analysis to evaluate the effectiveness of all available fetal surveillance methods in improving maternal and neonatal outcomes.     

Masking of fetal supraventricular tachycardia by electronic monitoring artefact.

In a fetus of 42 weeks'' gestation electronic monitoring demonstrated a heart rate of 120 beats/min that lacked the normal variability. Auscultation with a fetoscope revealed the true rate to be 240 beats/min. When used in the external Doppler mode the fetal monitor had a 250-ms refractory period after the recognition of a fetal cardiac event. This precluded recognition of the next beat and produced the artefactual halving of the heart rate. With the increasing reliance upon electronic fetal monitoring, those practising obstetrics should be aware of the possibility of artefacts and ensure that they can recognize truly representative information about the fetus.     

Randomised controlled trial of cardiotocography versus Doppler auscultation of fetal heart at admission in labour in low risk obstetric population

ObjectiveTo compare the effect of admission cardiotocography and Doppler auscultation of the fetal heart on neonatal outcome and levels of obstetric intervention in a low risk obstetric population.DesignRandomised controlled trial.SettingObstetric unit of teaching hospitalParticipantsPregnant women who had no obstetric complications that warranted continuous monitoring of fetal heart rate in labour.InterventionWomen were randomised to receive either cardiotocography or Doppler auscultation of the fetal heart when they were admitted in spontaneous uncomplicated labour.ResultsThere were no significant differences in the incidence of metabolic acidosis or any other measure of neonatal outcome among women who remained at low risk when they were admitted in labour. However, compared with women who received Doppler auscultation, women who had admission cardiotocography were significantly more likely to have continuous fetal heart rate monitoring in labour (odds ratio 1.49, 95% confidence interval 1.26 to 1.76), augmentation of labour (1.26, 1.02 to 1.56), epidural analgesia (1.33, 1.10 to 1.61), and operative delivery (1.36, 1.12 to 1.65).ConclusionsCompared with Doppler auscultation of the fetal heart, admission cardiotocography does not benefit neonatal outcome in low risk women. Its use results in increased obstetric intervention, including operative delivery.

What is already known on this topic

The admission cardiotocogram is a short recording of the fetal heart rate immediately after admission to the labour wardOpinion varies about its value in identifying a potentially compromised fetusIn low risk women, the incidence of intrapartum fetal compromise is low

What this study adds

Compared with Doppler auscultation of the fetal heart, admission cardiotocography has no benefit on neonatal outcome in low risk womenAdmission cardiotocography results in increased obstetric intervention, including operative delivery     

Fetal distress and the condition of newborn infants.

In a prospective audit of the obstetric management of 1210 consecutive deliveries the association was investigated between the need for operative delivery for fetal distress during labour and the condition of the newborn infant. Operative delivery was performed for only 11.5% of the newborn infants with severe acidosis at birth (umbilical artery pH less than 7.12, base deficit greater than 12 mmol (mEq)/1), 24.1% of those with an Apgar score less than 7 at one minute, and 15.8% of those with both severe acidosis and a one minute Apgar score less than 7. Most of the infants delivered operatively were in a vigorous condition at birth and did not have severe acidosis. Fetal blood sampling was done in 4.0% of labours. As none of the fetal blood values were less than 7.20 and only three of the infants sampled in utero suffered severe acidosis at birth, fetal blood sampling would have had to be performed much more often to provide a useful guide to metabolic state at birth. While the large majority of "at risk" fetuses had continuous fetal heart rate monitoring in labour, this had not been provided in 48.7% of the labours of infants with severe acidosis, 38.7% of infants with a one minute Apgar score less than 7, and 47.4% of infants with both severe acidosis and a one minute Apgar score less than 7. Continuous fetal heart rate monitoring was associated with a much higher incidence of operative delivery for fetal distress than was intermittent fetal heart rate auscultation. These results suggest an urgent need to review present methods for assessing the intrapartum condition of the fetus, making the diagnosis of fetal distress, and assessing the condition of the infant at birth.     

Midwife managed delivery unit: a randomised controlled comparison with consultant led care.

OBJECTIVE--To examine whether intrapartum care and delivery of low risk women in a midwife managed delivery unit differs from that in a consultant led labour ward. DESIGN--Pragmatic randomised controlled trial. Subjects were randomised in a 2:1 ratio between the midwives unit and the labour ward. SETTING--Aberdeen Maternity Hospital, Grampian. SUBJECTS--2844 low risk women, as defined by existing booking criteria for general practitioner units in Grampian. 1900 women were randomised to the midwives unit and 944 to the labour ward. MAIN OUTCOME MEASURES--Maternal and perinatal morbidity. RESULTS--Of the women randomised to the midwives unit, 647 (34%) were transferred to the labour ward antepartum, 303 (16%) were transferred intrapartum, and 80 (4%) were lost to follow up. 870 women (46%) were delivered in the midwives unit. Primigravid women (255/596, 43%) were significantly more likely to be transferred intrapartum than multi-gravid women (48/577, 8%). Significant differences between the midwives unit and labour ward were found in monitoring, fetal distress, analgesia, mobility, and use of episiotomy. There were no significant differences in mode of delivery or fetal outcome. CONCLUSIONS--Midwife managed intrapartum care for low risk women results in more mobility and less intervention with no increase in neonatal morbidity. However, the high rate of transfer shows that antenatal criteria are unable to determine who will remain at low risk throughout pregnancy and labour.     

Isolation of Fetal ECG Signals from Abdominal ECG Using Wavelet Analysis

ObjectiveMonitoring the heartbeat of the fetus during pregnancy is a vital part in determining their health. Current fetal heart monitoring techniques lack the accuracy in fetal heart rate monitoring and features acquisition, resulting in diagnostic medical issues. The demand for a reliable method of non-invasive fetal heart monitoring is of high importance.MethodElectrocardiogram (ECG) is a method of monitoring the electrical activity produced by the heart. The extraction of the fetal ECG (FECG) from the abdominal ECG (AECG) is challenging since both ECGs of the mother and the baby share similar frequency components, adding to the fact that the signals are corrupted by white noise. This paper presents a method of FECG extraction by eliminating all other signals using AECG. The algorithm is based on attenuating the maternal ECG (MECG) by filtering and wavelet analysis to find the locations of the FECG, and thus isolating them based on their locations. Two signals of AECG collected at different locations on the abdomens are used. The ECG data used contains MECG of a power of five to ten times that of the FECG.ResultsThe FECG signals were successfully isolated from the AECG using the proposed method through which the QRS complex of the heartbeat was conserved, and heart rate was calculated. The fetal heart rate was 135 bpm and the instantaneous heart rate was 131.58 bpm. The heart rate of the mother was at 90 bpm with an instantaneous heart rate of 81.9 bpm.ConclusionThe proposed method is promising for FECG extraction since it relies on filtering and wavelet analysis of two abdominal signals for the algorithm. The method implemented is easily adjusted based on the power levels of signals, giving it great ease of adaptation to changing signals in different biosignals applications.     

Detection and Processing Techniques of FECG Signal for Fetal Monitoring

Fetal electrocardiogram (FECG) signal contains potentially precise information that could assist clinicians in making more appropriate and timely decisions during labor. The ultimate reason for the interest in FECG signal analysis is in clinical diagnosis and biomedical applications. The extraction and detection of the FECG signal from composite abdominal signals with powerful and advance methodologies are becoming very important requirements in fetal monitoring. The purpose of this review paper is to illustrate the various methodologies and developed algorithms on FECG signal detection and analysis to provide efficient and effective ways of understanding the FECG signal and its nature for fetal monitoring. A comparative study has been carried out to show the performance and accuracy of various methods of FECG signal analysis for fetal monitoring. Finally, this paper further focused some of the hardware implementations using electrical signals for monitoring the fetal heart rate. This paper opens up a passage for researchers, physicians, and end users to advocate an excellent understanding of FECG signal and its analysis procedures for fetal heart rate monitoring system.     

Online Detection of Fetal Acidemia during Labour by Testing Synchronization of EEG and Heart Rate: A Prospective Study in Fetal Sheep

Severe fetal acidemia during labour can result in life-lasting neurological deficits, but the timely detection of this condition is often not possible. This is because the positive predictive value (PPV) of fetal heart rate (FHR) monitoring, the mainstay of fetal health surveillance during labour, to detect concerning fetal acidemia is around 50%. In fetal sheep model of human labour, we reported that severe fetal acidemia (pH<7.00) during repetitive umbilical cord occlusions (UCOs) is preceded ∼60 minutes by the synchronization of electroencephalogram (EEG) and FHR. However, EEG and FHR are cyclic and noisy, and although the synchronization might be visually evident, it is challenging to detect automatically, a necessary condition for bedside utility. Here we present and validate a novel non-parametric statistical method to detect fetal acidemia during labour by using EEG and FHR. The underlying algorithm handles non-stationary and noisy data by recording number of abnormal episodes in both EEG and FHR. A logistic regression is then deployed to test whether these episodes are significantly related to each other. We then apply the method in a prospective study of human labour using fetal sheep model (n = 20). Our results render a PPV of 68% for detecting impending severe fetal acidemia ∼60 min prior to pH drop to less than 7.00 with 100% negative predictive value. We conclude that this method has a great potential to improve PPV for detection of fetal acidemia when it is implemented at the bedside. We outline directions for further refinement of the algorithm that will be achieved by analyzing larger data sets acquired in prospective human pilot studies.     

Is fetal heart rate monitoring sufficiently sensitive to detect changes during labour?

Although fetal monitoring is a common clinical procedure, there is little quantitative evidence that it can detect changes occurring during labour. We present quantitative data comparing the first and second stage of labour, from 21 labours resulting in a normal fetal outcome. A range of fetal heart rate variables was calculated from the output of a fetal heart rate monitor. Significant changes were detected in baseline fetal heart rate (P < 0.005), heart rate variability (P < 0.05), number of dips (P < 0.01).and their depth (P < 0.01). The results encourage confidence in the sensitivity of fetal monitoring for the detection of changes in a number of fetal heart rate variables during the course of labour.     

Fetal behaviour and the cardiovascular system

With increasing gestation both in the human and in animals clear fetal behavioural state cycles develop. Fetal heart rate patterns are closely related to the phenomenon of behavioural state. In this review article fetal heart rate patterns will be analysed in relation to particular behavioural states, individual movement patterns and diurnal variations. Attention will also be paid to maturational changes. Differences between human and animal states are emphasized. It is concluded, that understanding of the basic mechanisms underlying the normal heart rate patterns throughout gestation, improves the reliability of fetal surveillance.     

Antepartum fetal heart rate recording and subsequent fast transmission by a distributed microprocessor-based dedicated system

Fetal heart rate monitoring in high-risk pregnancies can require admission to hospital over prolonged periods, or the even less satisfactory alternative of routine weekly or sporadic outpatient monitoring. We have developed a digital system for distant fetal heart rate recording with the facility of later rapid transmission by telephone in the hospital. A completed half-hour recording is transmitted to the central computer and permanently stored in less than 30 s, then immediately displayed for verbal reporting. One hundred and seventeen recordings have been made in 27 patients' home and of these 111 (95%) were easy to interpret. This expandable system meets the major functional requirements for practical and ecomonical antental fetal heart rate monitoring at a distance.     

Labour: when to worry.

To ensure an optimum result in pregnancy it is essential that the physician be alert in the antenatal period to recognize those women and their babies who are at risk during labour. Premature labour, with its attendant risk of respiratory distress syndrome in the newborn, continues to be an important factor in perinatal morbidity and mortality. Early recognition of predisposing factors and the judicious use of myometrial inhibiting agents have helped to reduce the incidence of fetal prematurity in these cases. A long interval between rupture of the membranes and delivery continues to be a danger to both mother and fetus. Delivery is recommended when gestation is beyond 36 weeks or when there are signs of incipient infection, and once labour has begun antibiotics should be used prophylactically. Failure of labour to progress should be recognized and managed aggressively in its early stages. Amniotomy and oxytocin infusion have reduced considerably the incidence of prolonged labour and its risks to both mother and fetus. The role of intrapartum monitoring of the fetal heart rate, measurement of the pH in the fetus''s scalp blood and assessment of amniotic fluid is discussed, as is the monitoring of maternal well-being.     

Antepartum fetal heart rate feature extraction and classification using empirical mode decomposition and support vector machine

Background  

Cardiotocography (CTG) is the most widely used tool for fetal surveillance. The visual analysis of fetal heart rate (FHR) traces largely depends on the expertise and experience of the clinician involved. Several approaches have been proposed for the effective interpretation of FHR. In this paper, a new approach for FHR feature extraction based on empirical mode decomposition (EMD) is proposed, which was used along with support vector machine (SVM) for the classification of FHR recordings as 'normal' or 'at risk'.     

Fetal arrhythmias: Diagnosis and management

This article reviews important features for improving the diagnosis and management of fetal arrhythmias. The normal fetal heart rate ranges between 110 and 160 beats per minute. A fetal heart rate is considered abnormal if the heart rate is beyond the normal ranges or the rhythm is irregular. The rate, duration, and origin of the rhythm and degree of irregularity usually determine the potential for hemodynamic consequences. Most of the fetal rhythm disturbances are the result of premature atrial contractions (PACs) and are of little clinical significance. Other arrhythmias include tachyarrhythmias (heart rate in excess of 160 beats/min) such as atrioventricular (AV) reentry tachycardia, atrial flutter, and ventricular tachycardia, and bradyarrhythmias (heart rate <110 beats/min) such as sinus node dysfunction, complete heart block (CHB) and long QT syndrome (which is associated with sinus bradycardia and pseudo-heart block).     

Continuous Fetal Heart Rate Monitoring and Tocodynamometry in Routine Obstetrical Care,Fetal Stress and Non-Stress Testing,and Labor Induction in the Chimpanzee (Pan troglodytes)

The use of continuous fetal heart rate (FHR) and uterine pressure monitoring in the chimpanzee (Pan troglodytes) by external Doppler transducer and tocodynamometer is described in 1) the routine obstetrical assessment of fetal well-being, 2) oxytocin challenge (stress) testing (OCT) and non-stress testing (NST) for the diagnosis of in utero fetal distress, and 3) induction of labor by intravenous oxytocin infusion, by surgical rupture of the chorio-amniotic membranes (amniotomy), or by a combination of these techniques, as an alternative to Caesarean section for clinical, managemental, or experimental purposes. FHR traces were analyzed during a total of 57 term pregnancies for three basic characteristics: baseline rate, variability, and periodic pattern. Results indicated that continuous FHR monitoring in the chimpanzee can provide a valuable tool for fetal assessment and management of labor in any attempt to reduce the unacceptably high annual incidence of perinatal and neonatal infant mortality reported in the U.S.     

Using nonlinear features for fetal heart rate classification

Fetal heart rate (FHR) is used to evaluate fetal well-being and enables clinicians to detect ongoing hypoxia during delivery. Routine clinical evaluation of intrapartum FHR is based on macroscopic morphological features visible to the naked eye. In this paper we evaluated conventional features and compared them to the nonlinear ones in the task of intrapartum FHR classification. The experiments were performed using a database of 217 FHR records with objective annotations, i.e. pH measurement. We have proven that the addition of nonlinear features improves accuracy of classification. The best classification results were achieved using a combination of conventional and nonlinear features with sensitivity of 73.4%, specificity of 76.3%, and F-measure of 71.9%. The best selected nonlinear features were: Lempel Ziv complexity, Sample entropy, and fractal dimension estimated by Higuchi method. Since the results of automatic signal evaluation are easily reproducible, the process of FHR evaluation can become more objective and may enable clinicians to focus on additional non-cardiotocography parameters influencing the fetus during delivery.     

Fractal Analysis and Hurst Parameter for Intrapartum Fetal Heart Rate Variability Analysis: A Versatile Alternative to Frequency Bands and LF/HF Ratio

Background

The fetal heart rate (FHR) is commonly monitored during labor to detect early fetal acidosis. FHR variability is traditionally investigated using Fourier transform, often with adult predefined frequency band powers and the corresponding LF/HF ratio. However, fetal conditions differ from adults and modify spectrum repartition along frequencies.

Aims

This study questions the arbitrariness definition and relevance of the frequency band splitting procedure, and thus of the calculation of the underlying LF/HF ratio, as efficient tools for characterizing intrapartum FHR variability.

Study Design

The last 30 minutes before delivery of the intrapartum FHR were analyzed.

Subjects

Case-control study. A total of 45 singletons divided into two groups based on umbilical cord arterial pH: the Index group with pH ≤ 7.05 (n = 15) and Control group with pH > 7.05 (n = 30).

Outcome Measures

Frequency band-based LF/HF ratio and Hurst parameter.

Results

This study shows that the intrapartum FHR is characterized by fractal temporal dynamics and promotes the Hurst parameter as a potential marker of fetal acidosis. This parameter preserves the intuition of a power frequency balance, while avoiding the frequency band splitting procedure and thus the arbitrary choice of a frequency separating bands. The study also shows that extending the frequency range covered by the adult-based bands to higher and lower frequencies permits the Hurst parameter to achieve better performance for identifying fetal acidosis.

Conclusions

The Hurst parameter provides a robust and versatile tool for quantifying FHR variability, yields better acidosis detection performance compared to the LF/HF ratio, and avoids arbitrariness in spectral band splitting and definitions.