Fetal heart rate patterns in growth-restricted fetal sheep induced by chronic fetal placental embolization

The peripheral chemoreflex and fetal defenses against intrapartum hypoxic-ischemic brain injury at term gestation

Fetal hypoxemia is ubiquitous during labor and, when severe, is associated with perinatal death and long-term neurodevelopmental disability. Adverse outcomes are highly associated with barriers to care, such that developing countries have a disproportionate burden of perinatal injury. The prevalence of hypoxemia and its link to injury can be obscure, simply because the healthy fetus has robust coordinated defense mechanisms, spearheaded by the peripheral chemoreflex, such that hypoxemia only becomes apparent in the minority of cases associated with stillbirth, severe metabolic acidemia or adverse neurodevelopmental outcomes. This represents only the extreme end of the spectrum, when defense mechanisms have failed due to severe/prolonged hypoxemia, or the fetal defenses are compromised by additional risk factors. Understanding the fetal defenses to hypoxemia and when the fetus begins to decompensate is crucial to understanding perinatal health and disease, by linking antenatal health, intrapartum events, the neonatal trajectory and ultimately life-long neurodevelopmental health.

Physiological control of fetal heart rate variability during labour: Implications and controversies

The interpretation of fetal heart rate (FHR) patterns is the only available method to continuously monitor fetal wellbeing during labour. One of the most important yet contentious aspects of the FHR pattern is changes in FHR variability (FHRV). Some clinical studies suggest that loss of FHRV during labour is a sign of fetal compromise so this is reflected in practice guidelines. Surprisingly, there is little systematic evidence to support this observation. In this review we methodically dissect the potential pathways controlling FHRV during labour-like hypoxaemia. Before labour, FHRV is controlled by the combined activity of the parasympathetic and sympathetic nervous systems, in part regulated by a complex interplay between fetal sleep state and behaviour. By contrast, preclinical studies using multiple autonomic blockades have now shown that sympathetic neural control of FHRV was potently suppressed between periods of labour-like hypoxaemia, and thus, that the parasympathetic system is the sole neural regulator of FHRV once FHR decelerations are present during labour. We further discuss the pattern of changes in FHRV during progressive fetal compromise and highlight potential biochemical, behavioural and clinical factors that may regulate parasympathetic-mediated FHRV during labour. Further studies are needed to investigate the regulators of parasympathetic activity to better understand the dynamic changes in FHRV and their true utility during labour. This article is protected by copyright. All rights reserved.

Relationship Between Deceleration Morphology and Phase Rectified Signal Averaging-Based Parameters During Labor

During labor, uterine contractions trigger the response of the autonomic nervous system (ANS) of the fetus, producing sawtooth-like decelerations in the fetal heart rate (FHR) series. Under chronic hypoxia, ANS is known to regulate FHR differently with respect to healthy fetuses. In this study, we hypothesized that such different ANS regulation might also lead to a change in the FHR deceleration morphology. The hypothesis was tested in an animal model comprising nine normoxic and five chronically hypoxic fetuses that underwent a protocol of umbilical cord occlusions (UCOs). Deceleration morphologies in the fetal inter-beat time interval (FRR) series were modeled using a trapezoid with four parameters, i.e., baseline b, deceleration depth a, UCO response time τ u and recovery time τ r . Comparing normoxic and hypoxic sheep, we found a clear difference for τ u (24.8±9.4 vs. 39.8±9.7 s; p < 0.05), a (268.1±109.5 vs. 373.0±46.0 ms; p < 0.1) and Δτ = τ u - τ r (13.2±6.9 vs. 23.9±7.5 s; p < 0.05). Therefore, the animal model supported the hypothesis that hypoxic fetuses have a longer response time τ u and larger asymmetry Δτ as a response to UCOs. Assessing these morphological parameters during labor is challenging due to non-stationarity, phase desynchronization and noise. For this reason, in the second part of the study, we quantified whether acceleration capacity (AC), deceleration capacity (DC), and deceleration reserve (DR), computed through Phase-Rectified Signal Averaging (PRSA, known to be robust to noise), were correlated with the morphological parameters. DC, AC and DR were correlated with τ u , τ r and Δτ for a wide range of the PRSA parameter T (Pearson's correlation ρ > 0.8, p < 0.05). In conclusion, deceleration morphologies have been found to differ between normoxic and hypoxic sheep fetuses during UCOs. The same difference can be assessed through PRSA based parameters, further motivating future investigations on the translational potential of this methodology on human data.

Absence of fetal heart rate cycling on the intrapartum cardiotocograph (CTG) is associated with intrapartum pyrexia and lower Apgar scores

BACKGROUND

Cycling consists of alternating periods of reduced and normal fetal heart variability, reflecting changes in fetal behavioral states. Occurrence of active and quiet sleep cycles is considered to be a hallmark of fetal autonomic nervous system integrity, demonstrating healthy interaction between the parasympathetic and sympathetic nervous systems. Cycling is an overlooked feature in most international cardiotocography (CTG) guidelines. The authors tested the hypothesis that fetuses showing no cycling in the intrapartum period have poorer outcomes.

AIM

To investigate whether the absence of cycling at the commencement of intrapartum fetal monitoring is associated with poorer neonatal outcomes (umbilical arterial cord pH, Apgar scores and neonatal unit admission).

METHODS

Analysis of a database of sequentially acquired intrapartum CTG traces from a single center. Only cases of singleton pregnancies over 36 weeks gestation in cephalic presentation with recorded umbilical artery cord pH were considered. Neonatal outcomes were assessed based on umbilical cord artery pH, Apgar ≤7 at 5 min and unexpected admission to the neonatal unit. Intrapartum pyrexia, presence of meconium-stained amniotic fluid and mode of delivery were also recorded.

RESULTS

A total of 684 cases were analyzed. Absence of cycling from the beginning of the intrapartum CTG recording was noted in 5% of cases. Cases with no cycling were more likely to have maternal pyrexia (≥37.8 °C) (p = .006) and Apgars ≤7 at 5 min (p = .04). There was an association between increasing baseline fetal heart rate and the proportion of cases with no cycling. There was no significant difference between the two groups with regard to the mode of delivery or umbilical cord arterial pH <7.05 (p = .53).

CONCLUSION

Absence of cycling is associated with intrapartum maternal pyrexia and fetuses with the absence of cycling are more likely to have poorer perinatal outcomes measured by Apgar ≤ 7 at 5 min, despite no association with fetal acidosis. Results from this research were presented at the XXVI European Congress of Perinatal Medicine in September 2018.

The reliance on α-adrenergic receptor stimuli for blood pressure regulation in the chronically hypoxaemic fetus is not dependent on post-ganglionic activation

KEY POINTS

Chronic hypoxaemia is associated with intrauterine growth restriction (IUGR) and a predisposition to the development of hypertension in adult life. IUGR fetuses exhibit a greater reliance on α-adrenergic activation for blood pressure regulation. The fetal blood pressure response to post-ganglionic blockade is not different between control and IUGR fetuses. The decrease in mean arterial pressure is greater in the IUGR sheep fetus after α-adrenergic receptor blockade at the level of the vasculature and this is inversely related to fetal P O 2 . The increased reliance that the IUGR fetus has on α-adrenergic activation for maintenance of mean arterial pressure is not a result of increased post-ganglionic sympathetic activation.

ABSTRACT

Intrauterine growth restriction (IUGR) is associated with an increased risk of cardiovascular disease in adult life. Placental restriction (PR) in sheep results in chronic hypoxaemia and early onset IUGR with increased circulating plasma noradrenaline concentrations. These IUGR fetuses exhibit a greater decrease in mean arterial pressure (MAP) during α-adrenergic blockade. We aimed to determine the role of post-ganglionic sympathetic activation with respect to regulating MAP in IUGR fetal sheep. PR was induced by carunclectomy surgery prior to conception. Fetal vascular catheterization was performed at 110-126 days gestational age (GA) (term, 150 days) in nine control and seven PR-IUGR fetuses. The fetal blood pressure response to both a post-ganglionic and an α-adrenergic receptor blocker was assessed at 116-120 days GA and/or 129-131 days GA. The effect of both post ganglionic and α-adrenergic blockade on fetal blood pressure was then compared between control and IUGR fetuses at both GAs. There was no difference in the effect of post-ganglionic blockade on MAP in control and IUGR fetal sheep at either 116-120 days GA or 129-131 days GA. α-adrenergic receptor blockade decreased MAP to the same extent in both control and IUGR fetuses at 116-120 days GA. At 129-131 days GA, the drop in MAP in response to α-adrenergic receptor blockade was greater in IUGR fetuses than controls. There was a significant inverse relationship between the drop in MAP in response to α-adrenergic receptor blockade at both GAs with fetal P O 2 . Thus, the increased dependence on α-adrenergic activation for blood pressure regulation in the chronically hypoxaemic IUGR fetus is not a result of increased post-ganglionic sympathetic activation.

Intrapartum fetal heart rate between 150 and 160 bpm at or after 40 weeks and labor outcome

INTRODUCTION

A baseline fetal heart rate between 110 and 160 bpm is considered normal. However, among normal fetuses the average baseline heart rate has been shown to diminish progressively and the 90th centile of the fetal heart rate at 40 weeks of gestation has been consistently found at around 150 bpm. The aim of our study was to assess the labor and neonatal outcome of fetuses at 40 gestational weeks or beyond, whose intrapartum baseline fetal heart rate was between 150 and 160 bpm.

MATERIAL AND METHODS

Retrospective cohort study including singleton pregnancies with spontaneous onset of labor, gestational age between 40⁺⁰ and 42⁺⁰ weeks, category I CTG trace according to the FIGO guidelines 2015 with baseline fetal heart rate between 110 and 160 bpm during the first 60 minutes of active labor. Exclusion criteria were maternal hyperpyrexia at admission, fetal arrhythmias, maternal tachycardia (>110 bpm) and uterine tachysystole (>5 contractions/10 minutes). The following outcomes were compared between fetuses with a baseline ranging between 110 and 149 bpm and those with a baseline ranging between 150 and 160 bpm: incidence of meconium-stained amniotic fluid, intrapartum hyperpyrexia, mode of delivery, Apgar at 5 minutes <7, arterial pH <7.1 and Neonatal Intensive Care Unit admission, incidence of a composite adverse neonatal outcome.

RESULTS

In all, 1004 CTG traces were included in the analysis, 860 in Group 110-149 bpm and 144 in Group 150-160 bpm. Group 150-160 bpm had a significantly higher incidence of meconium-stained amniotic fluid (odds ratio [OR] 2.6; 95% CI 1.8-3.8), maternal intrapartum hyperpyrexia (OR 4.7; 95% CI 1.1-14.6), urgent/emergent cesarean section for suspected fetal distress (OR 13.4; 95% CI 3.3-54.3), Apgar <7 at 5th min (OR 9.13; 95% CI 1.5-55.1) and neonatal acidemia (OR 3.5; 95% CI 1.5-55.1). Logistic regression including adjustiing for potential confounders showed that fetal heart rate between 150 and 160 bpm is an independent predictor of meconium-stained amniotic fluid (adjusted odds ratio [aOR] 2.2; 95% CI 1.5-3.3), cesarean section during labor for fetal distress (aOR 10.7; 95% CI 2.9-44.6), neonatal acidemia (aOR 2.6; 95% CI 1.1-6.7) and adverse composite neonatal outcome (aOR 2.6; 95% CI 1.2-5.6).

CONCLUSIONS

In fetuses at 40 weeks or beyond, an intrapartum fetal heart rate baseline ranging between 150 and 160 bpm seems associated with a higher incidence of labor complications.

Maternal sildenafil impairs the cardiovascular adaptations to chronic hypoxaemia in fetal sheep

KEY POINTS

Fetal growth restriction induces a haemodynamic response that aims to maintain blood flow to vital organs such as the brain, in the face of chronic hypoxaemia Maternal sildenafil treatment impairs the hypoxaemia-driven haemodynamic response and potentially compromises fetal development.

ABSTRACT

Inadequate substrate delivery to a fetus results in hypoxaemia and fetal growth restriction (FGR). In response, fetal cardiovascular adaptations redirect cardiac output to essential organs to maintain oxygen delivery and sustain development. However, FGR infants remain at risk for cardiovascular and neurological sequelae. Sildenafil citrate (SC) has been examined as a clinical therapy for FGR, but also crosses the placenta and may exert direct effects on the fetus. We investigated the effects of maternal SC administration on maternal and fetal cardiovascular physiology in growth-restricted fetal sheep. Fetal sheep (0.7 gestation) underwent sterile surgery to induce growth restriction by single umbilical artery ligation (SUAL) or sham surgery (control, AG). Fetal catheters and flow probes were implanted to measure carotid and femoral arterial blood flows. Ewes containing SUAL fetuses were randomized to receive either maternal administration of saline or SC (36 mg i.v. per day) beginning 4 days after surgery, and continuing for 20 days. Physiological recordings were obtained throughout the study. Antenatal SC treatment reduced body weight by 32% and oxygenation by 18% in SUAL compared to AG. SC did not alter maternal or fetal heart rate or blood pressure. Femoral blood flow and peripheral oxygen delivery were increased by 49% and 30% respectively in SUALSC compared to SUAL, indicating impaired cardiovascular adaptation to chronic hypoxaemia. Antenatal SC directly impairs the fetal haemodynamic response to chronic hypoxaemia. Consideration of the consequences upon the fetus should be paramount when administering interventions to the mother during pregnancy.

Cardiorespiratory consequences of intrauterine growth restriction: Influence of timing, severity and duration of hypoxaemia

At birth, weight of the neonate is used as a marker of the 9-month journey as a fetus. Those neonates born less than the 10th centile for their gestational age are at risk of being intrauterine growth restricted. However, this depends on their genetic potential for growth and the intrauterine environment in which they grew. Alterations in the supply of oxygen and nutrients to the fetus will decrease fetal growth, but these alterations occur due to a range of causes that are maternal, placental or fetal in nature. Consequently, IUGR neonates are a heterogeneous population. For this reason, it is likely that these neonates will respond differently to interventions compared not only to normally grown fetuses, but also to other neonates that are IUGR but have travelled a different path to get there. Thus, a range of models of IUGR should be studied to determine the effects of IUGR on the development and function of the heart and lung and subsequently the impact of interventions to improve development of these organs. Here we focus on a range of models of IUGR caused by manipulation of the maternal, placental or fetal environment on cardiorespiratory outcomes.

Fetal heart rate variability with hypoxemia in an instrumented sheep model

OBJECTIVE

To examine the effect of hypoxemia on fetal heart rate (FHR) variability, using an instrumented pregnant sheep model.

METHODS

In this prospective study, 19 pregnant sheep were instrumented under general anesthesia, at a mean gestational age of 127 days. After a 5-day recovery period, hypoxemia was induced by attaching the mother to a rebreathing circuit. Hypoxemia was sustained for 120 min, following which it was reversed until maternal and fetal partial pressure of oxygen (pO₂ ) returned to baseline. FHR recordings at baseline, after 30 and 120 min of hypoxemia and at recovery were analyzed to calculate short-term variation (STV) in 16 epochs of 3.75 s, every minute. Phase-rectified signal averaging (window length (L) = 10, time (T) = 2 and scale (S) = 2) was used to calculate FHR acceleration (AC) and deceleration (DC) capacities.

RESULTS

At baseline, mean ± SD fetal pO₂ was 2.90 ± 0.38 kPa. Acute hypoxemia was associated with a significant reduction in mean pO₂ at 30 (1.62 ± 0.37 kPa) and 120 (1.51 ± 0.16 kPa) min. Mean ± SD fetal pO₂ at recovery was 2.86 ± 0.32 kPa. At baseline, median STV, AC and DC were 1.307 (interquartile range (IQR), 0.515-2.508) ms, 1.295 (IQR, 0.990-2.685) beats per minute (bpm) and 1.197 (IQR, 0.850-1.836) bpm, respectively. At 30 min of hypoxemia, the values were 1.323 (IQR, 0.753-2.744) ms, 1.696 (IQR, 1.310-3.013) bpm and 1.584 (IQR, 1.217-4.132) bpm, respectively. At 120 min of hypoxemia, they were 1.760 (IQR, 0.928-4.656) ms, 3.098 (IQR, 1.530-5.163) bpm and 3.054 (IQR, 1.508-4.522) bpm, respectively. At recovery, they changed to 0.962 (IQR, 0.703-1.154) ms, 1.228 (IQR, 1.071-2.234) bpm and 1.086 (IQR, 0.873-1.568) bpm, respectively. Hypoxemia for 30 and 120 min was associated with a significant increase in DC compared to baseline (P = 0.014 and 0.017, respectively). The changes in STV and AC were not significant.

CONCLUSION

Acute hypoxemia is associated with a significant increase in the DC of FHR in a fetal sheep model. Copyright © 2019 ISUOG. Published by John Wiley & Sons Ltd.

Does the saltatory pattern on cardiotocograph (CTG) trace really exist? The ZigZag pattern as an alternative definition and its correlation with perinatal outcomes

Background: The saltatory pattern (SP) has been defined by guidelines as a uniformly increased bandwidth of >25 beats per min lasting for 30 min. However, previous research suggest that it is very unusual to observe such a "uniform" increase in the bandwidth persisting for >30 min. Baseline fetal heart rate variability (FHRV) on cardiotocography reflects the integrity of the central nervous system. During labor, in the presence of a gradually-evolving hypoxia associated with the onset of metabolic acidosis, FHRV may be reduced. However, if a fetus is exposed to rapidly-evolving hypoxia, it may not have sufficient time to release catecholamines and the perfusion of central organs can be impaired. In such cases, simultaneous increased activity of the sympathetic nervous system to obtain more oxygen as well as enhanced parasympathetic activity to reduce the myocardial workload can lead to autonomic instability. This exaggerated autonomic response can be seen frequently on the cardiotocograph as a rapid, irregular, abrupt "up and down" fluctuation across the baseline (amplitude >25 beats per min). The authors have termed this pattern as "ZigZag" when apparent for a minimum of 1 min. It differs from the SP in terms of duration and uniformity of the bandwidth.Objective: To determine the incidence of the SP during labor as well as a shorter and less uniform version of the SP newly called "ZigZag pattern" (ZZP). The intention was to correlate them with perinatal outcomes, taking into account the duration of the ZZP.Study design: A retrospective analysis of 500 consecutive cardiotocograph traces was performed to identify saltatory patterns and ZigZag patterns of 1 and 2 min of duration. Apgar scores, umbilical cord pH values and admission to the Neonatal Unit were evaluated and correlated with the cardiotocograph findings.Results: Not a single case of the SP was observed. A ZZP of 1 min of duration (ZZP1) was identified in 30.1% of the CTG during the last hour prior to delivery; ZZP lasting for 2 min (ZZP2) were identified in 8.9% of cases during the same period. Apgar scores at 1 min of ≤7 were significantly more frequent in newborns where the ZZP was observed (36.7% in ZZP1 and 54.5% in ZZP2 versus 9.5% in fetuses without); similarly, the Apgar scores at 5 min of ≤7 were also more frequent when ZZP was observed (6.7% in ZZP1 and 13.6% in ZZP2 versus 1.1% in controls). Moderate acidosis (pH 7.0-7.10) was more common in fetuses with the ZZP (14.3% in ZZP1 and 15% in ZZP2) compared to those without (4.6 and 7.2%, respectively). Similarly, mild acidosis (pH 7.1-7.2) was more common with the ZZP (40.3% in ZZP1 and 35% in ZZP2 versus 27.6 and 31.7%, respectively without ZZP). The neonatal admission rate was significantly higher in fetuses with the ZZP (8.7% in ZZP1 and 11.4% in ZZP2 versus 1.1% in controls).Conclusions: In line with previous research, our study suggest that SP is an almost nonexistent phenomenon. Alternatively, the ZigZag pattern (ZZP) has been defined as an exaggerated, irregular, "up and down" fluctuation of the baseline variability with an amplitude of >25 beats per min, lasting for 1 min or longer. It represents autonomic instability during human labor and it differs from the SP in terms of uniformity and length. Newborns with a ZZP during active maternal pushing were found to have statistically-significant lower Apgar scores at the 1st and 5th min, moderate and mild acidosis in the umbilical artery and an 8.7-11.4-fold higher neonatal admission rate. Clinicians should stop oxytocin infusion and/or active maternal pushing to improve fetal oxygenation if the ZZP is observed.

Understanding Fetal Heart Rate Patterns That May Predict Antenatal and Intrapartum Neural Injury

Electronic fetal heart rate (FHR) monitoring is widely used to assess fetal well-being throughout pregnancy and labor. Both antenatal and intrapartum FHR monitoring are associated with a high negative predictive value and a very poor positive predictive value. This in part reflects the physiological resilience of the healthy fetus and the remarkable effectiveness of fetal adaptations to even severe challenges. In this way, the majority of "abnormal" FHR patterns in fact reflect a fetus' appropriate adaptive responses to adverse in utero conditions. Understanding the physiology of these adaptations, how they are reflected in the FHR trace and in what conditions they can fail is therefore critical to appreciating both the potential uses and limitations of electronic FHR monitoring.

Relationship Between Short Term Variability (STV) and Onset of Cerebral Hemorrhage at Ischemia-Reperfusion Load in Fetal Growth Restricted (FGR) Mice

Fetal growth restriction (FGR) is a risk factor exacerbating a poor neurological prognosis at birth. A disease exacerbating a poor neurological prognosis is cerebral palsy. One of the cause of this disease is cerebral hemorrhage including intraventricular hemorrhage. It is believed to be caused by an inability to autoregulate cerebral blood flow as well as immaturity of cerebral vessels. Therefore, if we can evaluate the function of autonomic nerve, cerebral hemorrhage risk can be predicted beforehand and appropriate delivery management may be possible. Here dysfunction of autonomic nerve in mouse FGR fetuses was evaluated and the relationship with cerebral hemorrhage incidence when applying hypoxic load to resemble the brain condition at the time of delivery was examined. Furthermore, FGR incidence on cerebral nerve development and differentiation was examined at the gene expression level. FGR model fetuses were prepared by ligating uterine arteries to reduce placental blood flow. To compare autonomic nerve function in FGR mice with that in control mice, fetal short term variability (STV) was measured from electrocardiograms. In the FGR group, a significant decrease in the STV was observed and dysfunction of cardiac autonomic control was confirmed. Among genes related to nerve development and differentiation, Ntrk and Neuregulin 1, which are necessary for neural differentiation and plasticity, were expressed at reduced levels in FGR fetuses. Under normal conditions, Neurogenin 1 and Neurogenin 2 are expressed mid-embryogenesis and are related to neural differentiation, but they are not expressed during late embryonic development. The expression of these two genes increased in FGR fetuses, suggesting that neural differentiation is delayed with FGR. Uterine and ovarian arteries were clipped and periodically opened to give a hypoxic load mimicking the time of labor, and the bleeding rate significantly increased in the FGR group. This suggests that FGR deteriorates cardiac autonomic control, which becomes a risk factor for cerebral hemorrhage onset at birth. This study demonstrated that cerebral hemorrhage risk may be evaluated before parturition for FGR management by evaluating the STV. Further, this study suggests that choosing an appropriate delivery timing and delivery method contributes to neurological prognosis improvement.

Use of radiotelemetry to assess perinatal cardiac function in the ovine fetus and newborn

The late gestation fetal ECG (fECG) has traditionally been difficult to characterize due to the low fECG signal relative to high maternal noise. Although new technologies have improved the feasibility of its acquisition and separation, little is known about its development in late gestation, a period in which the fetal heart undergoes extensive maturational changes. Here, we describe a method for the chronic implantation of radiotelemetry devices into late gestation ovine fetuses to characterize parameters of the fECG following surgery, throughout late gestation, and in the perinatal period. We found no significant changes in mean aortic pressure (MAP), heart rate (HR), or ECG in the 5 days following implantation; however, HR decreased in the first 24 h following the end of surgery, with associated increases in RR, PR, and QRS intervals. Over the last 14 days of fetal life, fetal MAP significantly increased, and HR significantly decreased, as expected. MAP and HR increased as labor progressed. Although there were no significant changes over time in the ECG during late gestation, the duration of the PR interval initially decreased and then increased as birth approached. These results indicate that although critical maturational changes occur in the late gestation fetal myocardium, the mechanisms that control the cardiac conduction are relatively mature in late gestation. The study demonstrates that radiotelemetry can be successfully used to assess fetal cardiac function, in particular conduction, through the process of labor and delivery, and may therefore be a useful tool for study of peripartum cardiac events.

Recognition of chronic hypoxia and pre-existing foetal injury on the cardiotocograph (CTG): Urgent need to think beyond the guidelines

Chronic utero-placental insufficiency may result in progressive hypoxia culminating in fetal decompensation and acidosis and this is termed 'chronic' or 'long-standing' hypoxia. It is essential to recognise the features of chronic hypoxia on the CTG trace so as to institute timely and appropriate action. The current guidelines may not capture a fetus who starts labour already compromised or limited in its ability to compensate for hypoxic or mechanical stresses during labour. The aim of this short review is to explore the CTG features that allow the clinician to recognise a fetus who may present with an antenatal insult such as chronic hypoxia, anaemia, infection, fetal arrhythmias and preexisting non-hypoxic brain injury.

Phase-rectified signal averaging method to predict perinatal outcome in infants with very preterm fetal growth restriction- a secondary analysis of TRUFFLE-trial

BACKGROUND

Phase-rectified signal averaging, an innovative signal processing technique, can be used to investigate quasi-periodic oscillations in noisy, nonstationary signals that are obtained from fetal heart rate. Phase-rectified signal averaging is currently the best method to predict survival after myocardial infarction in adult cardiology. Application of this method to fetal medicine has established significantly better identification than with short-term variation by computerized cardiotocography of growth-restricted fetuses.

OBJECTIVE

The aim of this study was to determine the longitudinal progression of phase-rectified signal averaging indices in severely growth-restricted human fetuses and the prognostic accuracy of the technique in relation to perinatal and neurologic outcome.

STUDY DESIGN

Raw data from cardiotocography monitoring of 279 human fetuses were obtained from 8 centers that took part in the multicenter European "TRUFFLE" trial on optimal timing of delivery in fetal growth restriction. Average acceleration and deceleration capacities were calculated by phase-rectified signal averaging to establish progression from 5 days to 1 day before delivery and were compared with short-term variation progression. The receiver operating characteristic curves of average acceleration and deceleration capacities and short-term variation were calculated and compared between techniques for short- and intermediate-term outcome.

RESULTS

Average acceleration and deceleration capacities and short-term variation showed a progressive decrease in their diagnostic indices of fetal health from the first examination 5 days before delivery to 1 day before delivery. However, this decrease was significant 3 days before delivery for average acceleration and deceleration capacities, but 2 days before delivery for short-term variation. Compared with analysis of changes in short-term variation, analysis of (delta) average acceleration and deceleration capacities better predicted values of Apgar scores <7 and antenatal death (area under the curve for prediction of antenatal death: delta average acceleration capacity, 0.62 [confidence interval, 0.19-1.0]; delta short-term variation, 0.54 [confidence interval, 0.13-0.97]; P=.006; area under the curve for prediction Apgar <7: average deceleration capacity <24 hours before delivery, 0.64 [confidence interval, 0.52-0.76]; short-term variation <24 hours before delivery, 0.53 [confidence interval, 0.40-0.65]; P=.015). Neither phase-rectified signal averaging indices nor short-term variation showed predictive power for developmental disability at 2 years of age (Bayley developmental quotient, <95 or <85).

CONCLUSION

The phase-rectified signal averaging method seems to be at least as good as short-term variation to monitor progressive deterioration of severely growth-restricted fetuses. Our findings suggest that for short-term outcomes such as Apgar score, phase-rectified signal averaging indices could be an even better test than short-term variation. Overall, our findings confirm the possible value of prospective trials based on phase-rectified signal averaging indices of autonomic nervous system of severely growth-restricted fetuses.

Accelerated acidosis in response to variable fetal heart rate decelerations in chronically hypoxic ovine fetuses

BACKGROUND

Due to limitations of technology, clinicians are typically unable to determine if human fetuses are normoxic or moderately, chronically hypoxic. Risk factors for chronic hypoxia include fetal growth restriction, which is associated with an increased incidence of oligohydramnios and thus a risk for umbilical cord occlusion (UCO) and variable fetal heart rate (FHR) decelerations. At delivery, fetal growth restriction infants (<3rd percentile) have nearly twice the incidence of low Apgar scores and umbilical pH <7.0. Despite the risks of oligohydramnios and intermittent UCO, there is little understanding of the acid/base responses rates of chronically hypoxic fetuses to variable FHR decelerations as might occur during human labor.

OBJECTIVE

We sought to compare the increase in base deficit (BD) among chronically hypoxic as compared to normoxic ovine fetuses in response to simulated mild, moderate, and severe variable FHR decelerations.

STUDY DESIGN

Near-term ovine fetuses were chronically prepared with brachial artery catheters and an inflatable umbilical cuff occluder. Following a recovery period, normoxic (n = 9) and spontaneously hypoxic (n = 5) fetuses were identified (arterial O2 saturation ≤55%). Both animal groups underwent graded, 1-minute occlusions every 2.5 minutes with 1 hour of mild (∼30 beats/min [bpm] decrease from baseline), 1 hour of moderate (∼60 bpm decrease from baseline), and up to 2 hours of severe (∼90 bpm decrease from baseline) variable FHR decelerations until fetal arterial pH reached 7.00, when occlusions were stopped.

RESULTS

Repetitive UCO resulted in development of acidosis (pH <7.0) in both groups. Hypoxic and normoxic fetuses demonstrated similar BD increases in response to both mild (0.39, interquartile range [IQR] 0.28-0.45 vs 0.26, IQR 0.01-0.30 mEq/L/10 min, P = .25) and severe (1.97, IQR 1.50-2.43 vs 1.51, IQR 0.97-2.45 mEq/L/10 min, P = .63) variable decelerations. However, moderate variable decelerations increased BD in hypoxic fetuses at 2.5 times the rate of normoxic fetuses (0.97, IQR 0.52-1.72 vs 0.39, IQR 0.23-0.47 mEq/L/10 min, P = .03). During the recovery period, hypoxic fetuses cleared BD slower than normoxic fetuses (0.08 ± 0.02 vs 0.12 ± 0.03 mEq/L/min, P = .02).

CONCLUSION

In comparison to normoxic fetuses, hypoxic fetuses can more rapidly progress to significant metabolic acidosis in response to moderate FHR variable decelerations, and more slowly recover with in utero resuscitation, likely a consequence of impaired placental function and fetal physiologic responses.

Parameters influence on acceleration and deceleration capacity based on trans-abdominal ECG in early fetal growth restriction at different gestational age epochs

OBJECTIVE

Intrauterine growth restriction (IUGR) is characterized by chronic nutrient deprivation and hypoxemia that alters the autonomous nervous system regulation of fetal heart rate variability (fHRV). Phase-rectified signal averaging (PRSA) is a new algorithm capable to identify periodic and quasi-periodic patterns of HR, and which is used to quantify the average acceleration and deceleration capacity (AC/DC) of the heart. The computation of AC/DC depends on the parameters T and s, which we set so that s=T. T and s determine the periodicities that can be detected (the larger T the smaller the frequency of oscillations for which the method is most sensitive). The aim of the study was to evaluate the influence of the parameter T on PRSA computation, based on trans-abdominally acquired fetal ECG (ta-fECG), in early IUGR (<34 weeks of gestation) at two different gestational age epochs.

STUDY DESIGN

AC/DC were calculated for different T values (1÷45) on fetal RR intervals derived from ta-fECG in 22 IUGR and in 37 appropriate for gestational age (AGA) fetuses matched for gestational age, in two gestational age epochs: very preterm group (≥26÷<30 weeks), and preterm group (≥30÷<34 weeks), respectively.

RESULTS

AC/DC were significantly lower in IUGR than in AGA fetuses for all T≥5 values (p<0.05). The best area under the receiver operating characteristic curve (AUC) in identifying IUGR at time of recording was observed for T9 [AUC AC-T9 0.87, 95% confidence interval (CI) 0.77-0.96; and AUC DC-T9 0.89, 95% CI 0.81-0.98), and in range of T 7÷15. In the same T interval, AC/DC were significantly lower in very preterm than in preterm IUGR group (p<0.05), while there were no differences in AGA fetuses at two gestational age epochs (p>0.05), respectively. The AUCs of AC-T9 and DC-T9 significantly outperformed that obtained by short-term variation (AUC 0.77, 95% CI 0.65-0.90; p=0.009 and p=0.003, respectively).

CONCLUSIONS

Our study shows that within the range of T parameter 1÷45, T=9 proved to be the best value to discriminate the AC and DC of the fetal heart rate of IUGR from AGA fetuses prior to 34 weeks of gestation. These significant differences are emphasized in very preterm gestational age epochs.

Acceleration and deceleration capacity of fetal heart rate in an in-vivo sheep model

Background

Fetal heart rate (FHR) variability is an indirect index of fetal autonomic nervous system (ANS) integrity. FHR variability analysis in labor fails to detect early hypoxia and acidemia. Phase-rectified signal averaging (PRSA) is a new method of complex biological signals analysis that is more resistant to non-stationarities, signal loss and artifacts. It quantifies the average cardiac acceleration and deceleration (AC/DC) capacity.

Objective

The aims of the study were: (1) to investigate AC/DC in ovine fetuses exposed to acute hypoxic-acidemic insult; (2) to explore the relation between AC/DC and acid-base balance; and (3) to evaluate the influence of FHR decelerations and specific PRSA parameters on AC/DC computation.

Methods

Repetitive umbilical cord occlusions (UCOs) were applied in 9 pregnant near-term sheep to obtain three phases of MILD, MODERATE, and SEVERE hypoxic-acidemic insult. Acid-base balance was sampled and fetal ECGs continuously recorded. AC/DC were calculated: (1) for a spectrum of T values (T = 1÷50 beats; the parameter limits the range of oscillations detected by PRSA); (2) on entire series of fetal RR intervals or on “stable” series that excluded FHR decelerations caused by UCOs.

Results

AC and DC progressively increased with UCOs phases (MILD vs. MODERATE and MODERATE vs. SEVERE, p<0.05 for DC  = 2–5, and AC  = 1–3). The time evolution of AC/DC correlated to acid-base balance (0.4<<0.9, p<0.05) with the highest for . PRSA was not independent from FHR decelerations caused by UCOs.

Conclusions

This is the first in-vivo evaluation of PRSA on FHR analysis. In the presence of acute hypoxic-acidemia we found increasing values of AC/DC suggesting an activation of ANS. This correlation was strongest on time scale dominated by parasympathetic modulations. We identified the best performing parameters (), and found that AC/DC computation is not independent from FHR decelerations. These findings establish the basis for future clinical studies.

Plasticity of cardiovascular function in snapping turtle embryos (Chelydra serpentina): chronic hypoxia alters autonomic regulation and gene expression

Reptile embryos tolerate large decreases in the concentration of ambient oxygen. However, we do not fully understand the mechanisms that underlie embryonic cardiovascular short- or long-term responses to hypoxia in most species. We therefore measured cardiac growth and function in snapping turtle embryos incubated under normoxic (N21; 21% O₂) or chronic hypoxic conditions (H10; 10% O₂). We determined heart rate (fH) and mean arterial pressure (Pm) in acute normoxic (21% O₂) and acute hypoxic (10% O₂) conditions, as well as embryonic responses to cholinergic, adrenergic, and ganglionic pharmacological blockade. Compared with N21 embryos, chronic H10 embryos had smaller bodies and relatively larger hearts and were hypotensive, tachycardic, and following autonomic neural blockade showed reduced intrinsic fH at 90% of incubation. Unlike other reptile embryos, cholinergic and ganglionic receptor blockade both increased fH. β-Adrenergic receptor blockade with propranolol decreased fH, and α-adrenergic blockade with phentolamine decreased Pm. We also measured cardiac mRNA expression. Cholinergic tone was reduced in H10 embryos, but cholinergic receptor (Chrm2) mRNA levels were unchanged. However, expression of adrenergic receptor mRNA (Adrb1, Adra1a, Adra2c) and growth factor mRNA (Igf1, Igf2, Igf2r, Pdgfb) was lowered in H10 embryos. Hypoxia altered the balance between cholinergic receptors, α-adrenoreceptor and β-adrenoreceptor function, which was reflected in altered intrinsic fH and adrenergic receptor mRNA levels. This is the first study to link gene expression with morphological and cardioregulatory plasticity in a developing reptile embryo.

The fetal heart rate response to hypoxia: insights from animal models

This article examines recent studies that have systematically dissected features of fetal heart rate responses to labor that may help identify developing fetal compromise, such as the slope of the deceleration, overshoot, and variability. Although repeated deep decelerations are never necessarily benign, fetuses with normal placental reserve can fully compensate even for frequent deep but brief decelerations for surprisingly prolonged intervals before developing profound acidosis and hypotension.

Aetiology and pathogenesis of IUGR

Intrauterine growth restriction (IUGR) is a major cause of perinatal mortality and morbidity. A complex and dynamic interaction of maternal, placental and fetal environment is involved in ensuring normal fetal growth. An imbalance or lack of coordination in this complex system may lead to IUGR. Animal studies have given us an insight into some aspects of the basic pathophysiology of IUGR, and recent technologies such as Doppler studies of maternal and fetal vessels have added further information. The aetiologies of IUGR are diverse, involving multiple complex mechanisms, which make understanding of the pathophysiology difficult. However, particular focus is placed on the mechanisms involved in uteroplacental insufficiency as a cause of IUGR, as (1) it is common, (2) outcome can be good if timing of delivery is optimal and (3) it may be amenable to therapy in the future. While the research into the pathophysiology of IUGR continues, there have been interesting discoveries related to the genetic contribution to IUGR and the intrauterine programming of adult-onset diseases attributed to IUGR.

The intrapartum deceleration in center stage: a physiologic approach to the interpretation of fetal heart rate changes in labor

One of the most distinctive features of fetal heart rate recordings in labor is the deceleration. In clinical practice, there has been much confusion about the types of decelerations and their significance. In the present review, we examined uteroplacental perfusion in labor, describe the pathophysiologic condition of decelerations, and explain some of the reasons behind the confusion about the terminology. We summarize recent studies that systematically have dissected the features of variable decelerations that may help to identify developing fetal compromise, such as the slope of the deceleration, overshoot, and variability changes. Although no pattern of repeated deep decelerations is necessarily benign, fetuses with normal placental reserve can compensate fully, even for frequent deep but brief decelerations, for surprisingly prolonged intervals before the development of profound acidosis and hypotension. This tolerance reflects the remarkable ability of the fetus to adapt to repeated hypoxia. We propose that, rather than focus on descriptive labels, clinicians should be trained to understand the physiologic mechanisms of fetal heart rate decelerations and the patterns of fetal heart rate change that indicate progressive loss of fetal compensation.

Auditory processing deficits in growth restricted fetuses affect later language development

An increased risk for language deficits in infants born growth restricted has been reported in follow-up studies for more than 20 years, suggesting a relation between fetal auditory system development and later language learning. Work with animal models indicate that there are at least two ways in which growth restriction could affect the development of auditory perception in human fetuses: a delay in myelination or conduction and an increase in sensorineural threshold. Systematic study of auditory function in growth restricted human fetuses has not been reported. However, results of studies employing low-risk fetuses delivering as healthy full-term infants demonstrate that, by late gestation, the fetus can hear, sound properties modulate behavior, and sensory information is available from both inside (e.g., maternal vascular) and outside (e.g., noise, voices, music) of the maternal body. These data provide substantive evidence that the auditory system is functioning and that environmental sounds are available for shaping neural networks and laying the foundation for language acquisition before birth. We hypothesize that fetal growth restriction affects auditory system development, resulting in atypical auditory information processing in growth restricted fetuses compared to healthy, appropriately-grown-for-gestational-age fetuses. Speech perception that lays the foundation for later language competence will differ in growth restricted compared to normally grown fetuses and be associated with later language abilities.

Morphologic alterations in ovine placenta and fetal liver following induced severe placental insufficiency

OBJECTIVES

Umbilical-placental embolization with microspheres has been used as a model of placental insufficiency and intrauterine growth restriction (IUGR). However, the effects of embolization on placental structure and organ morphology of the resulting IUGR fetus are relatively unexplored. In this study using ovine fetuses, we determined the location and distribution of microspheres within the placenta and explored the extent of placental and fetal organ morphologic changes induced by placental embolization. We hypothesized that microspheres administered into the umbilical circulation over 4 days would cause placental damage without significant morphologic alterations in fetal kidney or liver.

METHODS

Eleven pregnant sheep at 118 +/- 1 (SE) days' gestation were studied. In six fetuses, embolization was induced by injections of 15-microm diameter microspheres on 4 successive days into the fetal descending aorta proximal to the umbilical arteries. Five fetuses served as time controls.

RESULTS

In embolized fetuses, microspheres were detected in the placenta embedded in the fetal cytotrophoblastic layer or maternal parenchyma adjacent to villous cytotrophoblasts. Fetal cytotrophoblasts appeared normal except for loss of distinct separation between fetal and maternal cell layers. Microspheres were also detected in the fetal membranes within capillaries. The body weights of embolized fetuses were lower than controls, as were the body weight-normalized liver but not kidney weights. In the liver of the embolized fetuses, the number of hematopoietic cell clusters was markedly reduced, whereas the fetal kidneys appeared normal.

CONCLUSIONS

We conclude that after 4 days of umbilical-placental embolization, microspheres were concentrated at the fetal villi proximal to the apical maternal-fetal interface and in the fetal membranes. There were noticeable morphologic changes in the embolized placentas, with no apparent gross damage to the placenta. The reduction in fetal liver weight and liver extramedullary hematopoietic cell abundance associated with embolization may predispose the fetus to alterations in liver function that could persist after birth.

Restriction of placental growth results in greater hypotensive response to alpha-adrenergic blockade in fetal sheep during late gestation

Placental insufficiency resulting in restriction of fetal substrate supply and fetal hypoxaemia is a major cause of restricted fetal growth and increased neonatal morbidity. Fetal adaptations to placental restriction (PR) include increases in circulating catecholamines and cortisol and decreased fetal body growth, with relative sparing of brain growth. The mechanisms underlying the redistribution of fetal cardiac output in PR fetuses are not known and the aim of this study was to determine whether maintenance of fetal blood pressure (BP) in the PR fetus is dependent on alpha-adrenergic stimulation. PR was induced by removing the majority of uterine caruncles in the ewe before conception. Sterile vascular surgery was performed on seven PR and six control fetuses at 113-120 days' gestation (term = 150 +/- 3 days). Fetuses with a mean arterial PO2 < 17 mmHg between 123 and 127 days' gestation were defined as hypoxic. There was a greater fall (P < 0.05) in fetal BP during phentolamine infusion (i.v: 5 mg bolus, 0.2 mg kg(-1) min(-1) for 2 h) in the hypoxic PR group (-15 +/- 2 mmHg) compared with normoxic controls (-5 +/- 1 mmHg). The fall in fetal BP during phentolamine infusion was directly related to the level of fetal PO2. Fetal BP and HR responses to phenylephrine (i.v.: 40 microg kg(-1)) were not different between PR and control fetuses. The maintenance of BP in the chronically hypoxic fetus is therefore dependent on alpha-adrenergic activation, and this fetal adaptation to a suboptimal intrauterine environment pre-dates the development of significant growth restriction. While this adaptation may play a critical role in the redistribution of fetal cardiac output to ensure the sparing of brain growth, it may have adverse consequences for peripheral vascular function in the neonatal period and in adult life.

Fetal heart rate variability and brain stem injury after asphyxia in preterm fetal sheep

This study was undertaken to determine the mechanisms mediating changes in fetal heart rate variability (FHRV) during and after exposure to asphyxia in the premature fetus. Preterm fetal sheep at 0.6 of gestation (91 ± 1 days, term is 147 days) were exposed to either sham occlusion ( n = 10) or to complete umbilical cord occlusion for either 20 ( n = 7) or 30 min ( n = 10). Cord occlusion led to a transient increase in FHRV with abrupt body movements that resolved after 5 min. In the 30 min group there was a marked increase in FHRV in the final 10 min of occlusion related to abnormal atrial activity. After reperfusion, FHRV in both study groups was initially suppressed and progressively increased to baseline levels over the first 4 h of recovery. In the 20 min group this improvement was associated with return of normal EEG activity and movements. In contrast, in the 30 min group the EEG was abnormal with epileptiform activity superimposed on a suppressed background, which was associated with abnormal fetal movements. As the epileptiform activity resolved, FHRV fell and became suppressed for the remainder of the study. Histological assessment after 72 h demonstrated severe brain stem injury in the 30 min group but not in the 20 min group. In conclusion, during early recovery from asphyxia, epileptiform activity and associated abnormal fetal movements related to evolving neural injury can cause a confounding transient increase in FHRV, which mimics the normal pattern of recovery. However, chronic suppression of FHRV was a strong predictor of severe brain stem injury.

Redistribution of power spectrum of heart rate variability during acute umbilical artery embolism and hypoxemia in late-gestation fetal sheep

OBJECTS

Fetal heart rate variability (HRV) is subject to a number of factors, including fetal distress. The aim of this study was to investigate the power spectral distribution of fetal heart rate variability during acute hypoxemia following umbilical artery embolism and to test the hypothesis that the relative proportion of frequency domains in total power of HRV, reflects the changes in HRV during hypoxemia more closely than the absolute values.

METHODS

Acute hypoxemia was induced in seven catheterized late-gestation fetal sheep by repeated injections of microspheres to cause umbilical artery embolism. The very-low, low-, middle- and high-frequency domains (0-0.025, 0.025-0.125, 0.125-0.20, and 0.20-0.50 cycles/beat, respectively) were determined by power spectral analysis.

RESULTS

Umbilical artery embolism induced marked fetal hypoxemia, hypercapnia and acidosis, accompanied by an increase in heart rate and a decrease in arterial blood pressure. These changes were associated with the increase in power over the entire frequency range and in the relative power in the low-frequency range (P<0.01), and with decrease in the relative power in the high-frequency range (P<0.05). Correlations were found between the relative power in the low- and high-frequency ranges and PO2 and between the relative power in these ranges and mean arterial blood pressure (P<0.05), but not PCO2 or pH.

CONCLUSIONS

The present study indicates that acute hypoxemia induced by umbilical artery embolism leads to the redistribution of power spectral density of fetal HRV and that the relative proportion of individual frequency domains may reflect the changes in HRV during acute hypoxemia more closely than the absolute power values.

Placental insufficiency and its consequences

Placental insufficiency is a process leading to progressive deterioration in placental function and a decrease in transplacental transfer of oxygen and nutrients to the fetus. The resulting fetal hypoxemia is the major stimulus involved in the reduction in fetal growth as an attempt to reduce metabolic demands by the growing fetus. Fetal growth restriction (FGR) is the second cause of perinatal death after prematurity and can complicate up to 6% of all pregnancies. It is becoming apparent that its occurrence has major impacts on the fetus and placenta with consequences on the cardiovascular, metabolic and neurological development up to adulthood. We are just starting to unveil some of the basic mechanisms involved in this complex adaptation that may lead to reprogramming of fetal organs development mostly the heart, pancreas, lungs and brain. It is becoming clear that future research is needed to develop strategies to improve antenatal detection of FGR, in addition to reduce the risk of abnormal neurodevelopment during childhood, and onset of common diseases in adulthood following pregnancies complicated with placental insufficiency.

A longitudinal analysis of arterial dopler parameters in growth restricted fetuses

Doppler parameters enable noninvasive and direct detection of placental insufficiency and brain sparing effect, which occurs as an adaptive mechanism to chronic hypoxemia. It is of great interest if further changes of Doppler parameters, which occur after the detection of the first pathologic value, can anticipate a moment of fetal distress. We investigated growth-restricted fetuses with the brain sparing effect in the time interval between the detection of blood flow redistribution until the distress. The aim of our study was to evaluate longitudinally Doppler parameters in umbilical (Aum), medial cerebral (MCA), renal (AR) and femoral (AF) artery and find: 1) if there are significant changes in their value; 2) the character and time interval of these changes; and 3) if they differ from changes in biophysical profile (BFP). MATERIALS AND METHODS Prospective clinical study evaluated 35 pregnancies with fetal growth restriction. Fetuses were selected for the study if: 1) there were pathologic cerebral/umbilical (C/U) ratio, 2) at least four Doppler examinations in 3-4 days interval were performed and 3) prepartal fetal distress, defined as silent fetal heart rate pattern with spontaneous and late decelerations, was present. In 28 neonates after delivery umbilical artery gas and acid-base status was determined. Blood flow velocity waveforms were evaluated in Aum MCA, AR, and AF. Arterial blood flow was estimated by pulsatility index (Pi), while in Aum we also used: present end-diastolic velocity (PEDV) absent end-diastolic velocity (AEDV) and reverse end-diastolic velocity (REDV). All of the fetuses were monitored by cardiotocogram (CTG) once to twice a day and by BFP twice a week. Elective Cesarean section was done in the presence of distress, except if severe immaturity or extreme malnutrition occurred. RESULTS Etiological factors of placental insufficiency were: 1) hypertensive syndrome (n=26), 2) chronic renal disease (n=3), 3) primary antiphospholipid syndrome (n=2), 4) diabetes mellitus (n=1), 5) cardiac disease (n=1) and 6) unknown (n=2). Initial Doppler examination, with the detection of pathological C/U, was done in time interval between 26. to 32. weeks of gestation (wg) (29.4 ? 2.5) delivery was between 29. to 34. wg (32.2 ? 1.9); and average body weight was 1327 ? 245g. Pathological BFP was registered in 91.4% of fetuses. Cesarian section has not been done, in spite of distress, in two fetuses (5.7%) due to their extreme immaturity and/or malnutrition, so they died "in utero". Hypoxemia was registered in 96.4% (27/28) neonates, while acidosis in 71.4% (20/28). Neonatal morbidity was 93.9% (31/33), neonatal mortality 8.6% while perinatal mortality was 14.3%. We found high significant difference (P<0.001) in Pi Aum, Pi ACM and Pi AR in the time interval between the detection of pathological C/U ratio and fetal distress, while the difference was insignificant for the values of Pi AF (table). The value changes are characterized by: continuing increase of Pi Aum, with a maximum in the last week before the distress; biphasic character of PI MCA - tendency to decrease in the first two and significant increase in the last week; and significant increase of Pi AR one and a half week before the distress (table, graphic). Three weeks before the distress in 7 (53.8%) cases we registered PEDV, in 6 (46.2%) AEDV, while we didn`t register REDV in any case. In the last week there were 3 (8.6%) PEDV, 23 (65.7%) AEDV and 9 (25.7%) REDV.. DISSCUSSION Significant changes in Doppler parameters suggest that even after the blood redistribution in growth restricted hypoxemic fetuses further haemodynamic changes occur. Preterminal increase in Pi Aum can be due to: 1) release of leucotrien, tromboxan and free oxygen radicals and consecutive vasoconstriction in villous arteries; 2) increase of diastolic arterial pressure as a result of hypoxic-ishemic central nervous system (CNS) insult; 3) decreased combined heart minute volume in preterminal phase of hypoxemia. The increase of Pi MCA values is a result of hypoxic-ishemic CNS insult. As a consequence of hypoxia ischemia occurs by two mechanisms: local vasodilatatory agents production decrease, or due to the brain edema. The increase of Pi AR values can be explained by severe hypoxemia with the failure of local autoregulation of renal blood flow. The greatest changes in BFP values were registered in the first half, while in Doppler parameters in the second half of the studied interval suggesting that Doppler parameters more accurately announce fetal distress. We can conclude the following: 1) fetal distress appears after the presence hypoxic-ischemic CNS insult, and therefore late when sequels are concerned; 2) if the fetus is mature, elective delivery should be planed after the appearance of pathological C/U ratio, or with the pathological BFP at the latest, in order to avoid post-hypoxic sequels; 3) if the fetus is immature, pregnancy can be prolonged safely, in spite of pathological C/U ratio and BFP, with intensive monitoring of Doppler parameters until the detection of their increased values.

Fetal umbilical vascular response to chronic reductions in uteroplacental blood flow in late-term sheep

OBJECTIVE

The present study was designed to determine the effects of chronic reduction in uterine blood flow (UBF) on umbilical blood flow (UmbBF) and fetal cardiovascular hemodynamics and oxygenation.

STUDY DESIGN

Sixteen sheep with singleton pregnancies were instrumented on gestational day (GD) 110; an externally adjustable vascular occluder was placed on the common internal iliac artery. UBF in control animals rose from 867 +/- 61 mL/min on GD 115 to 1520 +/- 158 mL/min (n = 8) on GD 138, whereas UBF in restricted animals was maintained at 750 +/- 50 mL/min (n = 8).

RESULTS

UmbBF in control animals increased from 472 +/- 25 mL/min to 744 +/- 58 mL/min over the study period from GD 115 to GD 138. This was associated with normal gestational increases in fetal arterial pressure and significant reductions in calculated umbilical vascular resistance. Although restricted animals initially had a similar UmbBF on GD 115, UmbBF rose only to 545 +/- 43 mL/min over the study period (control vs restricted, P <.008). Although fetal arterial pressure showed normal gestational changes, umbilical vascular resistance failed to decrease over gestation in restricted animals as it did in control animals. Fetal heart rate and oxygenation showed normal changes in both groups.

CONCLUSION

Chronic reduction in UBF prevents umbilical vascular resistance from undergoing normal gestational decreases, leading to significantly lower UmbBF. This altered umbilical perfusion pattern would be expected to significantly affect fetal delivery of oxygen and nutrients and ultimately fetal growth.

Periodic spectral components of fetal heart rate variability reflect the changes in cord arterial base deficit values: a preliminary report

Fetal distress changes the function of the autonomic nervous system. These changes are reflected in the fetal heart rate and can be quantified with power spectrum analysis of heart rate variability. The purpose of this study was to find out whether spectral components of fetal heart rate variability (FHRV) during labor are associated with fetal cord arterial base deficit values at birth. The association between FHRV and umbilical cord arterial base deficit was studied in 14 singleton fetuses with normal pregnancy at 35-40 weeks of gestation. Fetal ECG was recorded by scalp-electrode using a STAN Fetal ECG monitor (Cinventa Ab, Mölndal, Sweden). FHRV was quantified by computing Fast-Fourier-transformed heart rate (HR) spectra at three frequency bands: low-frequency (LF) 0.03-0.07 Hz, mid-frequency (MF) 0.07-0.13 Hz and high-frequency (HF) 0.13-1.0 Hz. We found that total FHRV and MF FHRV were lower in fetuses with cord arterial base deficit 8 to 12 mmol/L in comparison to the fetuses with normal cord arterial base deficit value (P=0.02 and P=0.01, respectively). A linear correlation was found between the spectral densities and the cord arterial base deficit values (r=0.4 and r=0.6, respectively). We conclude that the results suggest changes in the autonomic nervous cardiac control in fetuses with cord arterial base deficit between 8 to 12 mmol/L. The clinical applicability of our observations on FHRV in predicting fetal distress remains to be further studied.

Fetal heart rate variability changes during brief repeated umbilical cord occlusion in near term fetal sheep

OBJECTIVE

To determine whether changes in fetal heart rate variation during repeated umbilical cord occlusions reflect evolving cardiovascular compromise in near term fetal sheep.

DESIGN

Fetal heart rate variation, fetal mean arterial pressure, electroencephalogram (EEG) and acid-base status were measured during one minute umbilical cord occlusions, repeated either every five minutes (1:5 group) or every 2.5 minutes (1:2.5 group) for four hours or until mean arterial pressure fell below 20 mmHg for two successive occlusions.

SAMPLE

Fourteen chronically instrumented fetal sheep, mean gestation 126.3 (2.6) days.

RESULTS

Cord occlusion caused variable decelerations with initial sustained hypertension. In the 1:5 occlusion group mean arterial pressure remained elevated throughout, with little change in acid-base status (pH = 7.34 (0.07), base deficit = 1.3 (3.9) after 4 hours) and no significant change in fetal heart rate variation. In contrast, in the 1:2.5 group from the third occlusion there was progressive hypotension during occlusions, severe progressive metabolic acidaemia (pH 6.92 (0.1), base deficit 17.0 mmol/L (4.7) after the last occlusion) and marked EEG suppression (P < 0.01). Fetal heart rate variation increased with the onset of occlusions (P < 0.05) and then progressively fell with continued occlusions. During the last 30 minutes of occlusions, fetal heart rate variation was severely suppressed in four, but increased in two fetuses, while all six fetuses developed overshoot-instability of fetal heart rate and mean arterial pressure following each occlusion.

CONCLUSIONS

Acute progressive asphyxia was typically associated with an immediate, transient increase in fetal heart rate variation. Subsequently variation became suppressed in only two-thirds of fetuses during terminal acidaemia and hypotension. Fetal heart rate overshoot-instability may be a useful marker of fetal decompensation following variable decelerations.

Changes in surfactant-associated protein mRNA profile in growth-restricted fetal sheep

To test the hypothesis that chronic placental insufficiency resulting in fetal growth restriction causes an increase in fetal lung surfactant-associated protein (SP) gene expression, we embolized chronically catheterized fetal sheep (n = 6) daily using nonradioactive microspheres in the abdominal aorta for 21 days (between 0.74 and 0.88 of gestation) until fetal arterial oxygen content was reduced by approximately 40-50%. Control animals (n = 7) received saline only. Basal fetal plasma cortisol concentration was monitored. At the end of the experiment, fetal lung tissues were collected, and ratios of tissue levels of SP-A, SP-B, and SP-C mRNA to 18S rRNA were determined by standard Northern blot analysis. Total DNA content of fetal lungs was reduced by 30% in the embolized group compared with control group (P = 0.01). There was a 2.7-fold increase in fetal lung SP-A mRNA (P < 0.05) and a 3.2-fold increase in SP-B mRNA (P < 0.01) in the chronically embolized group compared with those in the control group. SP-A and SP-B mRNA tissue levels were highly correlated with the mean fetal plasma cortisol levels on days 20-21 (r = 0.90, P < 0.01 for SP-A mRNA and r = 0.94, P < 0.01 for SP-B mRNA). SP-C mRNA tissue levels were not significantly affected by placental insufficiency. We conclude that fetal growth restriction due to placental insufficiency is associated with alterations in fetal lung SP, suggesting enhanced lung maturation that was highly dependent on the degree of increase in fetal plasma cortisol levels.

The application of individualised fetal growth curves

Individually adjusted or 'customised' growth charts aim to optimise the assessment of fetal growth by taking individual variation into account, and by projecting an optimal curve which delineates the potential weight gain in each pregnancy. This results in an increased detection rate of true growth restriction and a reduction in false positive diagnoses for IUGR. An adjustable standard can apply across geographical boundaries, as individual variation exceeds that between different maternity populations.