Computer analysis of antepartum fetal heart rate: 1. Baseline determination

A consequent and reproducible determination of baseline is an essential prerequisite for objective interpretation of fetal heart rate. A fully automated off-line method of baseline determination has been developed and tested on 50 normal antepartum fetal heart rate recordings of two hours duration. The method is constructed around two functional units, a digital filter and a trim function, which interact in an iterative process. The results were evaluated in comparison with automated baseline determination according to Dawes and coworkers. A panel of 3 experts agreed that in 14 of the 50 recordings (28%), the new developed procedure resulted in a substantially better baseline fit. In the remaining 34 recordings (72%), baseline fit from both methods was judged as equivalent. The described procedure of baseline determination provides a solid base for automated detection of accelerations and decelerations in fetal heart rate recordings. It enables the study of the relation between the fetal heart rate pattern and fetal movements. Finally, it provides an objective tool for analysis of variables within the fetal heart rate with the highest predictive value with respect to fetal outcome.     

Changes in antepartum heart rate patterns with progressive deterioration of the fetal condition

In this paper changes in antepartum fetal heart rate (FHR) patterns are described, that occur with progressive deterioration of the fetal condition. The data on the relationship between heart rate patterns and fetal blood gas and pH values are reviewed. A possible rank ordering is presented in which changes in FHR pattern, body movements and blood flow velocity wave form patterns occur with progressive deterioration of the fetal condition.It is concluded that in small-for-date fetuses changes in heart rate and movement patterns are rather late signs of impairment, coinciding with fetal hypoxaemia. In general, heart rate variation falls below the norm at the same time as decelerations occur; there are, however, large inter-fetal differences. In general, abnormal Doppler velocity wave form patterns precede the occurrence of heart rate decelerations. Their impact on the timing of delivery is, however, still uncertain. The advantages of a numerical analysis of FHR patterns include identification of fetuses with low FHR variation, precision of the actual fetal condition and (at early gestation) longitudinal follow-up of fetuses with abnormal heart rate patterns.     

Criteria for the design of fetal heart rate analysis systems

Criteria are described for the automated analysis of fetal pulse intervals, fetal movements and of uterine contractions measured externally, antenatally and interactively on-line, for implementation on a personal computer interfaced to an appropriate fetal monitor, and tested on 10,000 records. Measurements of short and longer term fetal heart rate variation are compared; both are required to identify sinister records. Recall and display of records acquired on the same patient over several weeks has proved a useful diagnostic aid.     

The Antepartum Assessment of Fetal Well-being

Modern obstetrics is concerned with the health and well-being of both the mother and the unborn child. During the first two thirds of this century there was a pronounced decrease in maternal mortality and morbidity related to pregnancy. More recently, using the techniques of amniocentesis, antepartum fetal heart rate testing and ultrasound, obstetricians have been able to more accurately assess the health of a fetus. This knowledge has resulted in decreased perinatal mortality and morbidity and, when rigorously applied, a decrease in fetal loss.     

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.     

Cardiotocography in cows: A method for monitoring calves during delivery

Fetal ECG-electrodes and an intrauterine catheter were inserted into 15 Holstein-Friesian cows during their first stage of labor to make a cardiotocogram. Simultaneously, fetal heart rate and intrauterine pressure were recorded until completion of fetal expulsion. Immediatly post partum the viability of the calf was assessed by clinical evaluation and measurements of blood pH, base excess (BE) and pCO(2). Fetal heart rate patterns and their changes were evaluated according to standards used in human medicine. Basal fetal heart rate (90 to 120) in 10 calves gradually increased towards the end of parturition, with a marked loss of variability. Decelerations, coinciding with periods of increased intrauterine pressure, occurred in all cows. When decelerations occurred beyond the end of a contraction the calf was born in a poor condition. Accelerations were only recorded in two cows. Many of the fetal heart rate changes observed were similar to those which in human cardiotocography are considered to be signs of fetal distress. Further investigation is needed to establish the predictive value of fetal heart rate patterns in cows, which would be a welcome addition to improved fetal diagnostics during parturition.     

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.     

Canine fetal heart rate: Do accelerations or decelerations predict the parturition day in bitches?

Ultrasonography is a safe and efficient technique for monitoring fetal development and viability. One of the most important and widely used parameters to verify fetal viability is the fetal heart rate (HR). In human medicine, the fetal HR normally oscillates during labor in transient accelerations and decelerations associated with uterine contractions. The present study investigated whether these variations also occur in canine fetuses and its relationship to parturition. A cohort study was conducted in 15 pregnant bitches undergoing two-dimensional high-resolution ultrasonographic examination during the 8th and 9th week of gestation. Fetal HR was assessed in M-mode for 5 minutes in each fetus in all bitches. In addition, the bitches were monitored for clinical signs of imminent parturition. Associations between the HR, antepartum time, and delivery characteristics were evaluated with a Poisson regression model. Fetal HR acceleration and deceleration occurred in canine fetuses and predicted the optimal time of parturition. These findings can help veterinarians and sonographers better understand this phenomenon in canine fetuses.     

Amélioration de l’estimation du rythme cardiaque fœtal en utilisant les signaux Doppler directionnels et YIN

Techniques dedicated to the fetal heart rate detection identify the patterns that repeat themselves over the time. The heart rate estimation is algorithmically similar to the estimation of the fundamental frequency (pitch) of voice signals. The new YIN technique introduced for the estimation of the fundamental frequency is applied to fetal heart rate estimation from the directional Doppler signals. We compare the performances in terms of probability of detection and accuracy of the estimation of the technique YIN with those of the cross-correlation, implemented in the Oxford SONICAID? monitors. A better detection probability and accuracy of estimation of fetal heart rate was obtained in case of YIN.     

Increase in regularity of fetal heart rate variability with age.

It is generally assumed that fetal heart rate variability increases with gestation, reflecting prenatal development of the autonomic nervous system. We examined standard measures quantifying fetal heart rate variability, as well as a complexity measure, approximate entropy, in 66 fetal magnetocardiograms recorded from 22 healthy pregnant women between the 16th and 42nd week of gestation. In particular, regularity in the fetal RR interval time series was assessed on the basis of symbolic dynamics. The results showed that, beside an overall increase in fetal heart rate variability and complexity during pregnancy, there was also an increase in specific sets of binary patterns with low approximate entropy, i.e., a high degree of regularity. These sets were characterized by short epochs of heart rate acceleration and deceleration, and comparison with surrogate data confirmed that their random occurrence is rare. The results most likely reflect the influence of increasingly differentiated fetal behavioral states and transitions between them in association with fetal development.     

FiSBoG (fetal steroid binding glycoprotein) as a fetal function test

FiSBoG is a recently described fetal protein. It can be detected in the cord blood. It can be identified in maternal serum in late pregnancy. In this study the values in maternal serum in late pregnancy in 31 normal pregnancies were compared with 23 abnormal pregnancies: 4 twin pregnancies, 4 stillbirth, 4 cases of pre-eclampsia, 4 who had a significant antepartum haemorrhage and 7 who were small-for-dates, to assess its potential as a test of fetal well-being. FiSBoG appeared to have no significant role as a test of fetal well-being.     

Fetal exsanguination associated with antepartum hemorrhage.

Fetal bleeding in utero is infrequent. It is usually life-threatening but can be treated successfully in most cases if recognized early. Four cases are described and it is suggested that screening for fetal blood be done in all instances of antepartum hemorrhage.     

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.     

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.     

Self-similarity in variability of human heart variability at various stages of ontogenesis

We consider the potential of applying wavelet analysis to fluctuations found in physiological systems. We focus on cardiac interbeat interval time series (RR-intervals) from a group of young adults and children and fetus heart beat rate time series (antepartum cardiotocography), because the wavelet analysis of these heart rate dynamics may provide important practical diagnostic and prognostic information not obtainable with current approaches. We show that all the signals analyzed are self-similar and propose a method for estimating this scaling feature.     

Quantifying the Interactions between Maternal and Fetal Heart Rates by Transfer Entropy

Evidence of the short term relationship between maternal and fetal heart rates has been found in previous studies. However there is still limited knowledge about underlying mechanisms and patterns of the coupling throughout gestation. In this study, Transfer Entropy (TE) was used to quantify directed interactions between maternal and fetal heart rates at various time delays and gestational ages. Experimental results using maternal and fetal electrocardiograms showed significant coupling for 63 out of 65 fetuses, by statistically validating against surrogate pairs. Analysis of TE showed a decrease in transfer of information from fetus to the mother with gestational age, alongside the maturation of the fetus. On the other hand, maternal to fetal TE was significantly greater in mid (26–31 weeks) and late (32–41 weeks) gestation compared to early (16–25 weeks) gestation (Mann Whitney Wilcoxon (MWW) p<0.05). TE further increased from mid to late, for the fetuses with RMSSD of fetal heart rate being larger than 4 msec in the late gestation. This difference was not observed for the fetuses with smaller RMSSD, which could be associated with the quiet sleep state. Delay in the information transfer from mother to fetus significantly decreased (p = 0.03) from mid to late gestation, implying a decrease in fetal response time. These changes occur concomitant with the maturation of the fetal sensory and autonomic nervous systems with advancing gestational age. The effect of maternal respiratory rate derived from maternal ECG was also investigated and no significant relationship was found between breathing rate and TE at any lag. In conclusion, the application of TE with delays revealed detailed information on the fetal-maternal heart rate coupling strength and latency throughout gestation, which could provide novel clinical markers of fetal development and well-being.     

The interaction of behavioural state, heart rate and resistance index in the human fetus.

The association and possible interactions of fetal behavioural state, fetal heart rate and vascular resistance was studied in 23 healthy pregnant women between 36 and 40 weeks' gestation. Doppler flow velocity waveforms were obtained from fetal cerebral (anterior cerebral, internal carotid and basilar), descending aorta and umbilical arteries during fetal behavioural state 1F and repeated during 2F. The Resistance Index (RI) was used as a measure of vascular resistance. Decreased vascular resistance was observed in all vessels except the umbilical artery during fetal behavioural state 2F compared to 1F (P less than 0.001). A significant interaction was observed between fetal heart rate and fetal behavioural state on the RI of the vessels studied, with a greater negative slope for RI plotted against fetal heart rate in fetal behavioural state 2F (-0.00139) compared to 1F (0.00005) (P less than 0.001). We conclude that the transition from fetal behavioural state 1F to 2F is associated with a significant reduction in cerebral and systemic vascular resistance, with no apparent change in placental resistance. Furthermore, fetal behavioural state and fetal heart rate interact, demonstrating a stronger association of fetal heart rate and RI in fetal behavioural state 2F in keeping with an increase in baroreflex sensitivity at this time.     

Influence of alpha-chloralose on reflex control of the cardiovascular system in lambs

Alpha-chloralose is an anesthetic agent sometimes used for experiments in fetal and neonatal cardiovascular physiology. However, its effect on baseline cardiovascular variables and reflex control of the circulatory system has not been determined in young animals. We, therefore, investigated the effect of chloralose on blood pressure, heart rate and baroreflex activity in 12 lambs. Each lamb was anesthetized and a single-lumen catheter was placed in the inferior vena cava and a double-lumen balloon-tipped catheter was placed in the descending aorta. Following recovery from surgery for at least 48 h, blood pressure and heart rate were measured during quiet wakefulness and 30 min following the administration of polyethylene glycol-400 or alpha-chloralose (30, 60 or 90 mg/kg of body weight). Baroreflex activity was assessed by reflex slowing of the heart during an acute increase in blood pressure, produced by inflating the balloon in the descending aorta. Administration of polyethylene glycol-400 alone did not significantly affect blood pressure, heart rate or baroreflex activity. However, alpha-chloralose significantly decreased baroreflex activity in all the doses tested, compared to control responses obtained following the administration of polyethylene glycol-400 alone. Baseline blood pressure and heart rate were increased by 30 and 60 mg/kg of alpha-chloralose, whereas, 90 mg/kg decreased the blood pressure and did not change heart rate. We conclude that alpha-chloralose significantly alters baseline cardiovascular variables as well as reflex circulatory control in lambs. These effects should be taken into consideration when evaluating studies done during alpha-chloralose anesthesia.     

四维彩超技术在筛查胎儿先天性心脏病的应用价值分析

目的:探讨四维彩超技术在筛查胎儿先天性心脏病的应用价值。方法:择取我院2012年3月至2014年3月收治的行产前筛查的300例产妇为研究对象,采用四维彩色多普勒超声择取心脏三血管、四腔观、肺动脉分叉、上下腔静脉回流、动脉导管弓、主动脉弓等常规切面,予以胎心各腔血流及胎心率等多项检测,对胎儿是否存在先心病进行综合诊断,并综合胎儿大体解剖状况,与病理诊断及二维超声检查结果进行对比。结果:四维彩超检出率为6.67%,正确率为90.00%;二维超声检出率为6.00%,正确率为83.33%,两组比较差异具有统计学意义(P0.05)。结论:四维彩超技术在筛查胎儿先天性心脏病中具有至关重要的应用价值,有助于指导胎儿先天性心脏病早期治疗,保证患儿预后,值得临床借鉴。