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

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.

RidStress 2 randomised controlled trial protocol: an Australian phase III clinical trial of intrapartum sildenafil citrate or placebo to reduce emergency caesarean birth for fetal distress in women with small or suboptimally grown infants at term (≥37 weeks)

INTRODUCTION

Small for gestational age (SGA) infants are at increased risk of fetal distress in labour requiring emergency operative birth (by caesarean section (CS), vacuum or forceps). We have previously shown that maternal oral sildenafil citrate (SC) in labour halves the need for operative birth for suspected fetal distress in women with appropriately grown term infants.

METHODS AND ANALYSIS

RidStress 2 is a phase III randomised, double-blinded, placebo-controlled trial of 660 women with an SGA or suboptimally grown fetus (estimated fetal weight or abdominal circumference<10th centile for gestational age) planning a vaginal birth at term. The trial will determine whether oral intrapartum SC (50 mg eight hourly) reduces the relative risk of emergency CS for fetal distress compared with placebo. The primary outcome is CS for fetal distress, and the secondary outcomes are any operative birth for fetal distress, cost-effectiveness of SC treatment and 2-year childhood neurodevelopmental outcomes. To detect a 33% reduction in the primary outcome from 30% to 20% for an alpha of 0.05 and power of 80% with 10% dropout, requires approximately 660 women (330 in each arm). This sample size will also yield >90% power to detect a similar reduction for the secondary outcome of any operative birth (CS or instrumental vaginal birth) for fetal distress.

ETHICS AND DISSEMINATION

Ethics approval was granted by the Mater Misericordiae Limited Human Research Ethics Committee (EC00332) on 11 September 2020. We plan to disseminate the results of this randomised controlled trial through presentations at scientific meetings and peer-reviewed journals, adhering to all relevant reporting guidelines.

TRIAL REGISTRATION NUMBER

RidStress 2 is registered with the Australian New Zealand Clinical Trials Registry (ACTRN12621000354886, 29/03/2021) and the Therapeutic Goods Association of Australia (date registered: 16 March 2021).

Fetal heart rate responses in chronic hypoxaemia with superimposed repeated hypoxaemia consistent with early labour: a controlled study in fetal sheep

OBJECTIVE

Deceleration area (DA) and capacity (DC) of the fetal heart rate can help predict risk of intrapartum fetal compromise. However, their predictive value in higher risk pregnancies is unclear. We investigated whether they can predict the onset of hypotension during brief hypoxaemia repeated at a rate consistent with early labour in fetal sheep with pre-existing hypoxaemia.

DESIGN

Prospective, controlled study.

SETTING

Laboratory.

SAMPLE

Chronically instrumented, unanaesthetised near-term fetal sheep.

METHODS

One-minute complete umbilical cord occlusions (UCOs) were performed every 5 minutes in fetal sheep with baseline p_a O₂ <17 mmHg (hypoxaemic, n = 8) and >17 mmHg (normoxic, n = 11) for 4 hours or until arterial pressure fell <20 mmHg.

MAIN OUTCOME MEASURES

DA, DC and arterial pressure.

RESULTS

Normoxic fetuses showed effective cardiovascular adaptation without hypotension and mild acidaemia (lowest arterial pressure 40.7 ± 2.8 mmHg, pH 7.35 ± 0.03). Hypoxaemic fetuses developed hypotension (lowest arterial pressure 20.8 ± 1.9 mmHg, P < 0.001) and acidaemia (final pH 7.07 ± 0.05). In hypoxaemic fetuses, decelerations showed faster falls in FHR over the first 40 seconds of UCOs but the final deceleration depth was not different to normoxic fetuses. DC was modestly higher in hypoxaemic fetuses during the penultimate (P = 0.04) and final (P = 0.012) 20 minutes of UCOs. DA was not different between groups.

CONCLUSION

Chronically hypoxaemic fetuses had early onset of cardiovascular compromise during labour-like brief repeated UCOs. DA was unable to identify developing hypotension in this setting, while DC only showed modest differences between groups. These findings highlight that DA and DC thresholds need to be adjusted for antenatal risk factors, potentially limiting their clinical utility.

Fetal growth restriction and stillbirth: Biomarkers for identifying at risk fetuses

Fetal growth restriction (FGR) is a major cause of stillbirth, prematurity and impaired neurodevelopment. Its etiology is multifactorial, but many cases are related to impaired placental development and dysfunction, with reduced nutrient and oxygen supply. The fetus has a remarkable ability to respond to hypoxic challenges and mounts protective adaptations to match growth to reduced nutrient availability. However, with progressive placental dysfunction, chronic hypoxia may progress to a level where fetus can no longer adapt, or there may be superimposed acute hypoxic events. Improving detection and effective monitoring of progression is critical for the management of complicated pregnancies to balance the risk of worsening fetal oxygen deprivation in utero, against the consequences of iatrogenic preterm birth. Current surveillance modalities include frequent fetal Doppler ultrasound, and fetal heart rate monitoring. However, nearly half of FGR cases are not detected in utero, and conventional surveillance does not prevent a high proportion of stillbirths. We review diagnostic challenges and limitations in current screening and monitoring practices and discuss potential ways to better identify FGR, and, critically, to identify the “tipping point” when a chronically hypoxic fetus is at risk of progressive acidosis and stillbirth.

Short-term morbidity and types of intrapartum hypoxia in the newborn with metabolic acidaemia: a retrospective cohort study

Objectives

To assess labour characteristics in relation to the occurrence of Composite Adverse neonatal Outcome (CAO) within a cohort of fetuses with metabolic acidaemia.

Design

Retrospective cohort study.

Setting

Three Italian tertiary maternity units.

Population

431 neonates born with acidaemia ≥36 weeks.

Methods

Intrapartum CTG traces were assigned to one of these four types of labour hypoxia: acute, subacute, gradually evolving and chronic hypoxia. The presence of CAO was defined by the occurrence of at least one of the following: Sarnat Score grade ≥2, seizures, hypothermia and death <7 days from birth.

Main outcome measures

To compare the type of hypoxia on the intrapartum CTG traces among the acidaemic neonates with and without CAO.

Results

The occurrence of a CAO was recorded in 15.1% of neonates. At logistic regression analysis, the duration of the hypoxia was the only parameter associated with CAO in the case of an acute or subacute pattern (odds ratio [OR] 1.3; 95% CI 1.02–1.6 and OR 1.04; 95% CI 1.0–1.1, respectively), whereas both the duration of the hypoxic insult and the time from PROM to delivery were associated with CAO in those with a gradually evolving pattern (OR 1.13; 95% CI 1.01–1.3 and OR 1.04; 95% CI 1.0–1.7, respectively). The incidence of CAO was higher in fetuses with chronic antepartum hypoxia than in those showing CTG features of intrapartum hypoxia (64.7 vs. 13.0%; P < 0.001).

Conclusions

The frequency of CAO seems related to the duration and the type of the hypoxic injury, being higher in fetuses showing CTG features of antepartum chronic hypoxia.

Tweetable abstract

This study demonstrates that in a large population of neonates with metabolic acidaemia at birth, the overall incidence of short‐term adverse outcome is around 15%. Such risk seems closely correlated to the duration and the type of hypoxic injury, being higher in fetuses admitted in labour with antepartum chronic hypoxia than those experiencing intrapartum hypoxia.

This study demonstrates that in a large population of neonates with metabolic acidaemia at birth, the overall incidence of short‐term adverse outcome is around 15%. Such risk seems closely correlated to the duration and the type of hypoxic injury, being higher in fetuses admitted in labour with antepartum chronic hypoxia than those experiencing intrapartum hypoxia.

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.

Distance to Healthy Metabolic and Cardiovascular Dynamics From Fetal Heart Rate Scale-Dependent Features in Pregnant Sheep Model of Human Labor Predicts the Evolution of Acidemia and Cardiovascular Decompensation

The overarching goal of the present work is to contribute to the understanding of the relations between fetal heart rate (FHR) temporal dynamics and the well-being of the fetus, notably in terms of predicting the evolution of lactate, pH and cardiovascular decompensation (CVD). It makes uses of an established animal model of human labor, where 14 near-term ovine fetuses subjected to umbilical cord occlusions (UCO) were instrumented to permit regular intermittent measurements of metabolites lactate and base excess, pH, and continuous recording of electrocardiogram (ECG) and systemic arterial blood pressure (to identify CVD) during UCO. ECG-derived FHR was digitized at the sampling rate of 1,000 Hz and resampled to 4 Hz, as used in clinical routine. We focused on four FHR variability features which are tunable to temporal scales of FHR dynamics, robustly computable from FHR sampled at 4 Hz and within short-time sliding windows, hence permitting a time-dependent, or local, analysis of FHR which helps dealing with signal noise. Results show the sensitivity of the proposed features for early detection of CVD, correlation to metabolites and pH, useful for early acidosis detection and the importance of coarse time scales (2.5-8 s) which are not disturbed by the low FHR sampling rate. Further, we introduce the performance of an individualized self-referencing metric of the distance to healthy state, based on a combination of the four features. We demonstrate that this novel metric, applied to clinically available FHR temporal dynamics alone, accurately predicts the time occurrence of CVD which heralds a clinically significant degradation of the fetal health reserve to tolerate the trial of labor.

Identification of the Fetus at Risk for Metabolic Acidemia Using Continuous Fetal Heart Rate Monitoring

The fetal heart rate can be used to assess the current metabolic state of the fetus and predict the risk of the evolution of metabolic acidemia through the course of labor. In this chapter, we will present the pathophysiology of the development of fetal acidemia and provide an organized approach to identifying the risk of worsening acidemia using changes noted in the fetal heart rate pattern to allow for interventions that might alter this course.

Interpretation of Fetal Heart Rate Monitoring in the Clinical Context

Use of intrapartum fetal heart rate (FHR) monitoring has had limited success in preventing hypoxic injury to neonates. One of the most common limitations of FHR interpretation is the failure to consider chronic and acute clinical factors that may increase the risk of evolving acidemia. This manuscript reviews common clinical factors that may affect the FHR and should be considered when determining the need for early intervention based on changes in the FHR.

Management of the Category II Fetal Heart Rate Tracing

Management of the category II fetal heart rate (FHR) tracing presents a common challenge in obstetrics. Up to 80% of women will have a category II FHR tracing at some point during labor. Here we propose a management algorithm to identify specific features of the FHR tracing that correlate with risk for fetal acidemia, target interventions to address FHR decelerations, and guide clinicians about when to proceed toward operative vaginal delivery or cesarean to achieve delivery before there is a high risk for significant fetal acidemia with potential for neurological injury or death.

Fetal Cardiovascular Decompensation During Labor Predicted From the Individual Heart Rate Tracing: A Machine Learning Approach in Near-Term Fetal Sheep Model

Background: When exposed to repetitive umbilical cord occlusions (UCO) with worsening acidemia, fetuses eventually develop cardiovascular decompensation manifesting as pathological hypotensive arterial blood pressure (ABP) responses to fetal heart rate (FHR) decelerations. Failure to maintain cardiac output during labor is a key event leading up to brain injury. We reported that the timing of the event when a fetus begins to exhibit this cardiovascular phenotype is highly individual and was impossible to predict. Objective: We hypothesized that this phenotype would be reflected in the individual behavior of heart rate variability (HRV) as measured by root mean square of successive differences of R-R intervals (RMSSD), a measure of vagal modulation of HRV, which is known to increase with worsening acidemia. This is clinically relevant because HRV can be computed in real-time intrapartum. Consequently, we aimed to predict the individual timing of the event when a hypotensive ABP pattern would emerge in a fetus from a series of continuous RMSSD data. Study Design: Fourteen near-term fetal sheep were chronically instrumented with vascular catheters to record fetal arterial blood pressure, umbilical cord occluder to mimic uterine contractions occurring during human labor and ECG electrodes to compute the ECG-derived HRV measure RMSSD. All animals were studied over a ~6 h period. After a 1-2 h baseline control period, the animals underwent mild, moderate, and severe series of repetitive UCO. We applied the recently developed machine learning algorithm to detect physiologically meaningful changes in RMSSD dynamics with worsening acidemia and hypotensive responses to FHR decelerations. To mimic clinical scenarios using an ultrasound-based 4 Hz FHR sampling rate, we recomputed RMSSD from FHR sampled at 4 Hz and compared the performance of our algorithm under both conditions (1,000 Hz vs. 4 Hz). Results: The RMSSD values were highly non-stationary, with four different regimes and three regime changes, corresponding to a baseline period followed by mild, moderate, and severe UCO series. Each time series was characterized by seemingly randomly occurring (in terms of timing of the individual onset) increase in RMSSD values at different time points during the moderate UCO series and at the start of the severe UCO series. This event manifested as an increasing trend in RMSSD values, which counter-intuitively emerged as a period of relative stationarity for the time series. Our algorithm identified these change points as the individual time points of cardiovascular decompensation with 92% sensitivity, 86% accuracy and 92% precision which corresponded to 14 ± 21 min before the visual identification. In the 4 Hz RMSSD time series, the algorithm detected the event with 3 times earlier detection times than at 1,000 Hz, i.e., producing false positive alarms with 50% sensitivity, 21% accuracy, and 27% precision. We identified the overestimation of baseline FHR variability by RMSSD at a 4 Hz sampling rate to be the cause of this phenomenon. Conclusions: The key finding is demonstration of FHR monitoring to detect fetal cardiovascular decompensation during labor. This validates the hypothesis that our HRV-based algorithm identifies individual time points of ABP responses to UCO with worsening acidemia by extracting change point information from the physiologically related fluctuations in the RMSSD signal. This performance depends on the acquisition accuracy of beat to beat fluctuations achieved in trans-abdominal ECG devices and fails at the sampling rate used clinically in ultrasound-based systems. This has implications for implementing such an approach in clinical practice.

Forensic Analysis of Umbilical and Newborn Blood Gas Values for Infants at Risk of Cerebral Palsy

Cerebral palsy litigation cases account for the highest claims involving obstetricians/gynecologists, a specialty that ranks among the highest liability medical professions. Although epidemiologic studies indicate that only a small proportion of cerebral palsy (10-20%) is due to birth asphyxia, negligent obstetrical care is often alleged to be the etiologic factor, resulting in contentious medical-legal conflicts. Defense and plaintiff expert opinions regarding the etiology and timing of injury are often polarized, as there is a lack of established methodology for analysis. The objective results provided by umbilical cord and newborn acid/base and blood gas values and the established association with the incidence of cerebral palsy provide a basis for the forensic assessment of both the mechanism and timing of fetal neurologic injury. Using established physiologic and biochemical principles, a series of case examples demonstrates how an unbiased expert assessment can aid in both conflict resolution and opportunities for clinical education.

The effect of intrapartum oxygen supplementation on category II fetal monitoring

BACKGROUND

Maternal oxygen administration is a widely used intrauterine resuscitation technique for fetuses with category II electronic fetal monitoring patterns, despite a paucity of evidence on its ability to improve electronic fetal monitoring patterns.

OBJECTIVE

This study investigated the effect of intrapartum oxygen administration on Category II electronic fetal monitoring patterns.

STUDY DESIGN

This is a secondary analysis of a randomized trial conducted in 2016-2017, in which patients with fetuses at ≥37 weeks' gestation in active labor with category II electronic fetal monitoring patterns were assigned to 10 L/min of oxygen by face mask or room air until delivery. Trained obstetrical research nurses blinded to allocation extracted electronic fetal monitoring data. The primary outcome was a composite of high-risk category II features including recurrent variable decelerations, recurrent late decelerations, prolonged decelerations, tachycardia, or minimal variability 60 minutes after randomization to room air or oxygen. Secondary outcomes included individual components of the composite high-risk category II features, resolution of recurrent decelerations within 60 minutes of randomization, and total deceleration area. The outcomes between the room air and oxygen groups were compared using univariable statistics. Time-to-event analysis was used to compare time to resolution of recurrent decelerations between the groups. Paired analysis was used to compare the pre- and postrandomization outcomes within each group.

RESULTS

All 114 randomized patients (57 room air and 57 oxygen) were included in this analysis. There was no difference in resolution of recurrent decelerations within 60 minutes between the oxygen and room air groups (75.4% vs 86.0%; P=.15). The room air and oxygen groups had similar rates of composite high-risk category II features including recurrent variable decelerations, recurrent late decelerations, prolonged decelerations, tachycardia, and minimal variability 60 minutes after randomization. Time to resolution of recurrent decelerations and total deceleration area were similar between the room air and oxygen groups. Among patients who received oxygen, there was no difference in the electronic fetal monitoring patterns pre- and postrandomization. Similar findings were observed in the electronic fetal monitoring patterns pre- and postrandomization in room air patients.

CONCLUSION

Intrapartum maternal oxygen administration for category II electronic fetal monitoring patterns did not resolve high-risk category II features or hasten the resolution of recurrent decelerations. These results suggest that oxygen administration has no impact on improving category II electronic fetal monitoring patterns.

Effect of magnesium sulfate on baroreflex during acute hypoxemia in chronically instrumented fetal sheep

AIM

To investigate the effects of magnesium sulfate on fetal baroreflex in normoxemia or acute fetal hypoxemia.

METHODS

Fetal baroreflex response was elicited using phenylephrine (30 μg) in saline and magnesium sulfate in 8 chronically treated and instrumented fetal sheep. Hypoxemia was induced using nitrogen gas inflow for 30 min. Baroreflex, calculated as the ratio of the fetal heart rate change to the mean arterial pressure, was monitored after magnesium sulfate administration and in rapid and nonrapid eye movement (NREM) sleep states. Baroreflex was assessed in response to hypoxemia in control groups in both the rapid and NREM sleep states.

RESULTS

Baroreflex was not significantly affected by saline, magnesium sulfate and rapid or NREM sleep states in normoxemic sheep. Hypoxemia increased the baroreflex in the saline-treated group (hypoxemic vs normoxemic rapid eye movement sleep: 4.37 ± 2.48 vs 2.72 ± 0.83; P < 0.05; hypoxemic vs normoxemic NREM sleep: 4.30 ± 1.47 vs 3.15 ± 0.83; P < 0.001). Magnesium sulfate decreased the baroreflex in the hypoxemic fetuses (magnesium sulfate hypoxemic vs. control normoxemic fetuses: 1.42 ± 0.92 vs 3.15 ± 0.83, P < 0.05).

CONCLUSION

The hypoxemic fetal sheep, from the ewes that were receiving magnesium sulfate, showed a significantly reduced in the baroreflex response. In clinical practice, baroreflex-related decelerations in hypoxemic fetuses of mothers receiving magnesium sulfate should be carefully interpreted.

Intrapartum Fetal Heart Rate Tracing Among Small-for-Gestational Age Compared With Appropriate-for-Gestational-Age Neonates

OBJECTIVE

To compare fetal heart rate (FHR) patterns during the last hour of labor between small-for-gestational-age (SGA; birth weight less than the 10th percentile for gestational age) and appropriate-for-gestational-age (AGA; birth weight at the 10-90th percentile) neonates at 36 weeks of gestation or greater. We also compared the rate of cesarean delivery and composite neonatal morbidity among SGA and AGA newborns.

METHODS

This is a secondary analysis of a randomized trial of intrapartum fetal electrocardiographic ST-segment analysis. We excluded women with chorioamnionitis, insufficient duration of FHR tracing in the hour before delivery, and anomalous newborns. Fetal heart rate patterns were categorized by computerized pattern recognition software (PeriCALM Patterns). Composite neonatal morbidity was defined as any of the following: intrapartum fetal death, Apgar score 3 or less at 5 minutes, cord artery pH 7.05 or less, base deficit 12 mmol/L or greater, neonatal seizure, intubation at delivery, neonatal encephalopathy, and neonatal death. Logistic regression was used to evaluate the association between FHR patterns and SGA adjusted for magnesium sulfate exposure and stage of labor.

RESULTS

Of the 11,108 women randomized, 85% (n=9,402) met inclusion criteria, of whom 9% were SGA. In the last hour, the likelihood of accelerations was significantly lower among SGA than AGA neonates (72.4% vs 66.8%; P=.001). Variable decelerations lasting greater than 60 seconds, with depth greater than 60 beats per minute (bpm) or nadir less than 60 bpm, were significantly more common with SGA than AGA (all P<.001). The rate of late decelerations, prolonged decelerations, or bradycardia were similar between SGA and AGA (all P>.05). Cesarean delivery for fetal indications was significantly more common with SGA (7.0%) than AGA (4.0%; P<.001). The composite neonatal morbidity was 1.4% among SGA and 1.0% among AGA (odds ratio 1.40, 95% CI 0.74-2.64).

CONCLUSION

Although the FHR patterns in the last hour of labor differ among SGA and AGA neonates, as does the rate of cesarean delivery, the composite neonatal morbidity was similar.

The peripheral chemoreflex: indefatigable guardian of fetal physiological adaptation to labour

The fetus is consistently exposed to repeated periods of impaired oxygen (hypoxaemia) and nutrient supply in labour. This is balanced by the healthy fetus's remarkable anaerobic tolerance and impressive ability to mount protective adaptations to hypoxaemia. The most important mediator of fetal adaptations to brief repeated hypoxaemia is the peripheral chemoreflex, a rapid reflex response to acute falls in arterial oxygen tension. The overwhelming majority of fetuses are able to respond to repeated uterine contractions without developing hypotension or hypoxic-ischaemic injury. In contrast, fetuses who are either exposed to severe hypoxaemia, for example during uterine hyperstimulation, or enter labour with reduced anaerobic reserve (e.g. as shown by severe fetal growth restriction) are at increased risk of developing intermittent hypotension and cerebral hypoperfusion. It is remarkable to note that when fetuses develop hypotension during such repeated severe hypoxaemia, it is not mediated by impaired reflex adaptation, but by failure to maintain combined ventricular output, likely due to a combination of exhaustion of myocardial glycogen and evolving myocardial injury. The chemoreflex is suppressed by relatively long periods of severe hypoxaemia of 1.5-2 min, longer than the typical contraction. Even in this setting, the peripheral chemoreflex is consistently reactivated between contractions. These findings demonstrate that the peripheral chemoreflex is an indefatigable guardian of fetal adaptation to labour.

Correlation of a new index reflecting the fluctuation of parasympathetic tone and fetal acidosis in an experimental study in a sheep model

The autonomic nervous system plays a leading role in the control of fetal homeostasis. Fetal heart rate variability (HRV) analysis is a reflection of its activity. We developed a new index (the Fetal Stress Index, FSI) reflecting parasympathetic tone. The objective of this study was to evaluate this index as a predictor of fetal acid-base status. This was an experimental study on chronically instrumented fetal lambs (n = 11, surgery at 128 +/- 2 days gestational age, term = 145 days). The model was based on 75% occlusion of the umbilical cord for a maximum of 120 minutes or until an arterial pH ≤ 7.20 was reached. Hemodynamic, gasometric and FSI parameters were recorded throughout the experimentation. We studied the FSI during the 10 minutes prior to pH samplings and compared values for pH>7.20 and pH≤ 7.20. In order to analyze the FSI evolution during the 10 minutes periods, we analyzed the minimum, maximum and mean values of the FSI (respectively FSImin, FSImax and FSImean) over the periods. 11 experimentations were performed. During occlusion, the heart rate dropped with an increase in blood pressure (respectively 160(155-182) vs 106(101-120) bpm and 42(41-45) vs 58(55-62) mmHg after occlusion). The FSImin was 38.6 (35.2-43.3) in the group pH>7.20 and was higher in the group pH less than 7.20 (46.5 (43.3-52.0), p = 0.012). The correlation of FSImin was significant for arterial pH (coefficient of -0.671; p = 0.004) and for base excess (coefficient of -0.632; p = 0.009). The correlations were not significant for the other parameters. In conclusion, our new index seems well correlated with the fetal acid-base status. Other studies must be carried out in a situation close to the physiology of labor by sequential occlusion of the cord.

Potential adverse effects of antenatal melatonin as a treatment for intrauterine growth restriction: findings in pregnant sheep

BACKGROUND

Intrauterine growth restriction is a condition in which the fetus has a birthweight and/or length <10th percentile for the gestational age. Intrauterine growth restriction can be associated with various causes, among which is low uteroplacental perfusion and chronic hypoxia during gestation. Often, intrauterine growth-restricted fetuses have increased oxidative stress; therefore, agents that decrease oxidative stress and increase utero, placental, and umbilical perfusion have been proposed as a beneficial therapeutic strategy. In this scenario, melatonin acts as an umbilical vasodilator and a potent antioxidant that has not been evaluated in pregnancies under chronic hypoxia that induce fetal growth restriction. However, this neurohormone has been proposed as a pharmacologic therapy for complicated pregnancies.

OBJECTIVES

The aim of this study was to determine the effects of prenatal administration of melatonin during the last trimester of pregnancy on the biometry of the growth-restricted lambs because of developmental hypoxia. Further, we aimed to determine melatonin and cortisol levels and oxidative stress markers in plasma of pregnant ewes during the treatment.

STUDY DESIGN

High-altitude pregnant sheep received either vehicle (n = 5; 5 mL 1.4% ethanol) or melatonin (n = 7; 10 mg/kg(-1)day(-1) in 5 mL 1.4% ethanol) daily during the last one-third of gestation. Maternal plasma levels of melatonin, cortisol, antioxidant capacity, and oxidative stress were determined along treatment. At birth, neonates were examined, weighed, and measured (biparietal diameter, abdominal diameter, and crown-rump length).

RESULTS

Antenatal treatment with melatonin markedly decreased neonatal biometry and weight at birth. Additionally, melatonin treatment increased the length of gestation by 7.5% and shifted the time of delivery. Furthermore, the prenatal treatment doubled plasma levels of melatonin and cortisol and significantly improved the antioxidant capacity of the pregnant ewes.

CONCLUSIONS

Our findings indicate that antenatal melatonin induces further intrauterine growth restriction but improves the maternal plasma antioxidant capacity. Additional studies should address the efficiency and safety of antenatal melatonin before clinical attempts on humans.