Effects of maternal hyperoxia with and without normocapnia in uteroplacental and fetal Doppler studies

Maternal Oxygen Administration during Labor: A Controversial Practice

Oxygen administration to the mother is commonly performed during labor, especially in the case of a non-reassuring fetal heart rate, aiming to increase oxygen diffusion through the placenta to fetal tissues. The benefits and potential risks are controversial, especially when the mother is not hypoxemic. Its impact on placental gas exchange and the fetal acid-base equilibrium is not fully understood and it probably affects the sensible placental oxygen equilibrium causing a time-dependent vasoconstriction of umbilical and placental vessels. Hyperoxia might also cause the generation of radical oxygen species, raising concerns for the developing fetal cells. Moreover, this practice affects the maternal cardiovascular system, causing alterations of the cardiac index, heart rate and vascular resistance, and unclear effects on uterine blood flow. In conclusion, there is no evidence that maternal oxygen administration can provide any benefit in the case of a non-reassuring fetal heart rate pattern, while possible collateral effects warn of its utilization. Oxygen administration during labor should be reserved for cases of maternal hypoxia.

Chronic hypoxia in pregnant mice impairs the placental and fetal vascular response to acute hypercapnia in BOLD-MRI hemodynamic response imaging

INTRODUCTION

Brief hypercapnic challenge causes acute placental hypoperfusion with fetal brain sparing on BOLD-MRI. We hypothesize that this non-invasive imaging strategy can distinguish between normal pregnancy and chronic placental hypoperfusion (using the maternal hypoxia model).

METHODS

Eighteen pregnant female ICR mice were randomized to three groups: normoxia, late-onset hypoxia (12%O₂;E13.5-17.5) and early-onset hypoxia (12%O₂;E10.5-17.5). On E17.5, animals were imaged in a 4.7-T Bruker-Biospec MRI scanner. Fast coronal True-FISP was performed to identify organs of interest (placenta and fetal heart, liver and brain). BOLD-MRI was performed at baseline and during a 4-min hypercapnic challenge (5%CO₂). %-change in placental and fetal signal was analyzed from T2*-weighted gradient echo MR images. Following MRI, fetuses and placentas were harvested, weighed and immuno-stained.

RESULTS

In normoxic mice, hypercapnia caused reduction in BOLD-MRI signal in placenta (-44% ± 7%; p < 0.0001), fetal liver (-32% ± 7%; p < 0.0001) and fetal heart (-54% ± 12%; p < 0.002), with relative fetal brain sparing (-12% ± 5%; p < 0.0001). These changes were markedly attenuated in both hypoxia groups. Baseline fetal brain/placenta SI ratio was highest in normoxic mice (1.14 ± 0.017) and reduced with increasing duration of hypoxia (late-onset hypoxia: 1.00 ± 0.026; early-onset hypoxia: 0.91 ± 0.016; p = 0.02). Both hypoxic groups exhibited fetal growth restriction with prominent placental glycogen-containing cells, particularly in early-onset hypoxia. There was increased fetal neuro- and intestinal-apoptosis in early-onset hypoxia only.

CONCLUSIONS

BOLD-MRI with brief hypercapnic challenge distinguished between normoxia and both hypoxia groups, while fetal neuroapoptosis was only observed after early-onset hypoxia. This suggests that BOLD-MRI with hypercapnic challenge can identify chronic fetal asphyxia before the onset of irreversible brain injury.

Impact of intrauterine fetal resuscitation with oxygen on oxidative stress in the developing rat brain

Use of maternal oxygen for intrauterine resuscitation is contentious because of the lack of evidence for its efficacy and the possibility of fetal harm through oxidative stress. Because the developing brain is rich in lipids and low in antioxidants, it remains vulnerable to oxidative stress. Here, we tested this hypothesis in a term pregnant rat model with oxytocin-induced fetal distress followed by treatment with either room air or 100% oxygen for 6 h. Fetal brains from both sexes were subjected to assays for biomarkers of oxidative stress (4-hydroxynonenal, protein carbonyl, or 8-hydroxy-2'-deoxyguanosine), expression of genes mediating oxidative stress, and mitochondrial oxidative phosphorylation. Contrary to our hypothesis, maternal hyperoxia was not associated with increased biomarkers of oxidative stress in the fetal brain. However, there was significant upregulation of the expression of select genes mediating oxidative stress, of which some were male-specific. These observations, however, were not accompanied by changes in the expression of proteins from the mitochondrial electron transport chain. In summary, maternal hyperoxia in the setting of acute uteroplacental ischemia-hypoxia does not appear to cause oxidative damage to the developing brain.

Fetal cerebrovascular response to maternal hyperoxygenation in congenital heart disease: effect of cardiac physiology

OBJECTIVE

Fetal cerebrovascular resistance is influenced by several factors in the setting of intact autoregulation to allow for normal cerebral blood flow and oxygenation. Maternal hyperoxygenation (MH) allows for acute alterations in fetal physiology and can be a tool to test cerebrovascular reactivity in late-gestation fetuses. In this study, we utilized MH to evaluate cerebrovascular reactivity in fetuses with specific congenital heart disease (CHD).

METHODS

This was a cross-sectional study of fetuses with complex CHD compared to controls without CHD. CHD cases were grouped according to physiology into: left-sided obstructive lesion (LSOL), right-sided obstructive lesion (RSOL) or dextro-transposition of the great arteries (d-TGA). Subjects underwent MH testing during the third-trimester fetal echocardiogram. The pulsatility index (PI) was calculated for the fetal middle cerebral artery (MCA), umbilical artery (UA) and branch pulmonary artery (PA). The change in PI from baseline to during MH was compared between each CHD group and controls.

RESULTS

Sixty pregnant women were enrolled (CHD, n = 43; control, n = 17). In the CHD group, there were 27 fetuses with LSOL, seven with RSOL and nine with d-TGA. Mean gestational age was 33.9 (95% CI, 33.6-34.2) weeks. At baseline, MCA-PI Z-score was lowest in the LSOL group (-1.8 (95% CI, -2.4 to -1.2)) compared with the control group (-0.8 (95% CI, -1.3 to -0.3)) (P = 0.01). In response to MH, MCA-PI Z-score increased significantly in the control and d-TGA groups but did not change significantly in the LSOL and RSOL groups. The change in MCA-PI Z-score was significantly higher in the control group than in the LSOL group (0.9 (95% CI, 0.42-1.4) vs 0.12 (95% CI, -0.21 to 0.45); P = 0.03). This difference was more pronounced in the LSOL subgroup with retrograde aortic arch flow. Branch PA-PI decreased significantly in response to MH in all groups, with no difference in the change from baseline to MH between the groups, while UA-PI was unchanged during MH compared with at baseline.

CONCLUSIONS

The fetal cerebrovascular response to MH varies based on the underlying CHD diagnosis, suggesting that cardiovascular physiology may influence the autoregulatory capacity of the fetal brain. Further studies are needed to determine the clinical implications of these findings on long-term neurodevelopment in these at-risk children. © 2020 International Society of Ultrasound in Obstetrics and Gynecology.

Calling into question the future of hyperoxygenation in pregnancy

Maternal hyperoxygenation has been investigated as a potential diagnostic and therapeutic tool since the 1960s. Since then, it has been applied in many obstetric scenarios, both clinically and in the research setting. It is often administered without any determination of pre-hyperoxygenation maternal or fetal oxygen levels. Studies focussing on maternal oxygen therapy for the treatment of fetal growth restriction have been ongoing for over thirty years and there remains no clear evidence of benefit. Studies investigating the potential diagnostic or therapeutic role of maternal oxygen therapy in the setting of fetal congenital cardiac disease have reported varying success rates and some potentially worrying adverse effects. The purpose of this article is to review the effects of maternal hyperoxygenation on fetal and maternal health and to ascertain the safety of undertaking further clinical trials that employ the use of hyperoxygenation in pregnancy.

Prenatal prediction of neonatal haemodynamic adaptation after maternal hyperoxygenation

Abstract

The reactivity of the pulmonary vascular bed to the administration of oxygen is well established in the post-natal circulation. The vasoreactivity demonstrated by the fetal pulmonary artery Doppler waveform in response to maternal hyperoxia has been investigated. We sought to investigate the relationship between the reactivity of the fetal pulmonary arteries to hyperoxia and subsequent neonatal cardiac function in the early newborn period.

Methods

This explorative study with convenience sampling measured pulsatility index (PI), resistance index (RI), acceleration time (AT), and ejection time (ET) from the fetal distal branch pulmonary artery (PA) at baseline and following maternal hyperoxygenation (MH). Oxygen was administered for 10 min at a rate of 12 L/min via a partial non-rebreather mask. A neonatal functional echocardiogram was performed within the first 24 h of life to assess ejection fraction (EF), left ventricular output (LVO), and neonatal pulmonary artery AT (nPAAT). This study was conducted in the Rotunda Hospital, Dublin, Ireland.

Results

Forty-six women with a singleton pregnancy greater than or equal to 31 weeks’ gestational age were prospectively recruited to the study. The median gestational age was 35 weeks. There was a decrease in fetal PAPI and PARI following MH and an increase in fetal PAAT, leading to an increase in PA AT:ET. Fetuses that responded to hyperoxygenation were more likely to have a higher LVO (135 ± 25 mL/kg/min vs 111 ± 21 mL/kg/min, p < 0.01) and EF (54 ± 9% vs 47 ± 7%,p = 0.03) in the early newborn period than those that did not respond to MH prenatally. These findings were not dependent on left ventricular size or mitral valve (MV) annular diameter but were related to an increased MV inflow. There was no difference in nPAAT.

Conclusion

These findings indicate a reduction in fetal pulmonary vascular resistance (PVR) and an increase in pulmonary blood flow and left atrial return following MH. The fetal response to hyperoxia reflected an optimal adaptation to postnatal life with rapid reduction in PVR increasing measured cardiac output.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12884-020-03403-y.

The duration of intrapartum supplemental oxygen administration and umbilical cord oxygen content

BACKGROUND

Maternal oxygen (O₂) administration is a commonly performed intrauterine resuscitation technique though to improve fetal oxygenation. However, hyperoxygenation is known to be harmful in both neonates and adults. Currently, there are no formal recommendations on whether a certain dose or duration of O₂ may be most helpful in improving umbilical cord gases or neonatal outcomes.

OBJECTIVE

We tested the hypothesis that prolonged supplemental O₂ exposure during labor is associated with increased umbilical cord O₂ concentrations.

STUDY DESIGN

This was a planned secondary analysis of a randomized noninferiority trial comparing O₂ with room air in laboring patients. Patients were randomized to receive either 10 L/min O₂ or room air at any point during active labor when they developed a category II fetal heart tracing that would otherwise require resuscitation. The primary outcome variable for this analysis was partial pressure of O₂ in the umbilical vein. The secondary outcome variable was partial pressure of O₂ in the umbilical artery. These outcome variables were compared between patients with short durations of O₂ exposure and those with long durations of O₂ exposure, defined as <75th percentile and ≥75th percentile of duration, respectively. The outcomes were also compared among the groups that received room air, O₂ for short durations, and O₂ for long durations.

RESULTS

Among the 99 patients with paired and validated cord gases who were included in this analysis, the partial pressure of O₂ in the umbilical vein was significantly lower in patients who received O₂ supplementation for longer durations than in those who received O₂ for shorter durations (median interquartile range 25.5 [21.5-33] vs 32.5 [26.5-37.5] mm Hg; P<.03). There was no difference in the partial pressure of O₂ in the umbilical artery or other cord gases between the short and long duration O₂ supplementation groups. Other methods of intrauterine resuscitation were similar between the short and long duration O₂ supplementation groups. There was no difference in the partial pressure of O₂ in the umbilical artery or in the umbilical vein when the room air, short duration O₂ supplementation, and long duration O₂ supplementation groups were compared.

CONCLUSION

Longer durations of O₂ exposure are not associated with a higher partial pressure of O₂ in the umbilical cord. In fact, patients with longer durations of O₂ exposure had lower partial pressure of O₂ in the umbilical vein, suggesting impaired placental O₂ transfer with prolonged O₂ exposure.

Cerebral hemodynamic response to short-term maternal hyperoxygenation in fetuses with borderline small left hearts

BACKGROUND

Hypoxia delays brain maturation and contributes to neurodevelopmental morbidity in fetuses with congenital heart defects (CHDs). Maternal hyperoxygenation (MH) can, in theory, promote oxygen/nutrient delivery to the fetal brain, owing to an improved heart structure/function and increased fetal oxygen content. We aimed to determine whether MH alters fetal cerebral hemodynamics in fetuses with CHD.

METHODS

Twenty-eight fetuses with borderline small left hearts and 28 age-matched normal fetuses were enrolled and subdivided by gestational age (GA): 23^+ 0 ~ 27^+ 6 weeks and 28^+ 0 ~ 36^+ 6 weeks. The middle cerebral artery pulsatility index (MCA-PI), vascular index (VI), flow index (FI) and vascular/flow index (VFI) were measured with baseline room air, after 10 min of MH and after 10 min of recovery for all subjects.

RESULTS

MCA-PI, VI, FI and VFI did not differ with MH in the normal fetuses. In fetuses with borderline small left hearts, MCA-PI increased and VI, FI and VFI significantly decreased during the 3rd trimester (from 1.44 ± 0.27, 3.19 ± 0.87, 56.91 ± 9.19, and 1.30 ± 0.33 at baseline to 1.62 ± 0.15, 2.37 ± 0.37, 45.73 ± 4.59, and 0.94 ± 0.15 during MH, respectively, P < 0.05), but this response was not apparent during mid-gestation (p > 0.05). These parameters returned to the baseline levels during the recovery phase. The change in cerebral perfusion depended on the baseline MCA-PI and increased the combined cardiac index (CCOi).

CONCLUSIONS

MH alters the cerebral hemodynamics of fetuses with borderline small left hearts during the third trimester. Further investigation is needed to determine whether MH may benefit brain growth and neurodevelopment in this high-risk population.

Fetal acute cerebral vasoreactivity to maternal hyperoxia in low-risk pregnancies: a cross-sectional study

OBJECTIVE

To establish whether fetal cerebral vasoreactivity (CVR_O2 ), following maternal hyperoxia, is predicted by fetal cerebral and uteroplacental Doppler pulsatility indices (PI) at baseline, fetal pulmonary vasoreactivity to oxygen (PVR_O2 ), gestational age (GA), or sex.

METHODS

Pulsatility index of middle (MCA), anterior (ACA), posterior cerebral (PCA), umbilical (UA), uterine (UtA), and branch of the pulmonary arteries (PA) were obtained, by ultrasound, before (baseline), during (hyperoxia) and after 15 minutes of maternal administration of 8 L/min of 100% oxygen, through a non-rebreathing face mask, in normal singleton pregnancies within 20 to 38 weeks' gestation. CVR_O2 was defined as changes greater than zero in z score of PI of the cerebral arteries from baseline to hyperoxia. Logistic modeling was applied to identify CVR_O2 predictors.

RESULTS

A total of 97 pregnancies were eligible. In the overall population, median z scores of PI of MCA, ACA, and PCA did not differ between study phases. Based on the logistic model, baseline z scores for cerebral PI and GA were the best predictors of CVR_O2 .

CONCLUSIONS

In low-risk pregnancies, fetal CVR_O2 to hyperoxia does not occur uniformly but depends on cerebral PI and GA at baseline. These findings may provide useful reference points when oxygen is administered in high-risk pregnancies.

Hemodynamic Responses of the Placenta and Brain to Maternal Hyperoxia in Fetuses with Congenital Heart Disease by Using Blood Oxygen-Level Dependent MRI

Background Impaired brain development in fetuses with congenital heart disease (CHD) may result from inadequate cerebral oxygen supply in utero. Purpose To test whether fetal cerebral oxygenation can be increased by maternal oxygen administration, effects of maternal hyperoxia on blood oxygenation of the placenta and fetal brain were examined by using blood oxygenation level-dependent (BOLD) functional MRI. Materials and Methods In this prospective study, BOLD MRI was performed in 86 fetuses (56 healthy fetuses and 30 fetuses diagnosed with CHD) between 22 and 39 weeks gestational age (GA) from May 2015 to December 2017, with the following study design: phase I, 2-minute resting state at baseline (room air); phase II, 6-minute maternal hyperoxia with 100% oxygen; and phase III, 5.6-minute return to resting state. After motion correction, the signals were averaged over the placenta and fetal brain and converted to the change in R2* (ΔR2*). Fetuses with CHD were categorized into those with a single ventricle (SV) or two ventricles (TVs) and those with aortic obstruction (AO) or non-AO. Data were analyzed by using generalized linear mixed models controlling for GA and sex. Results Placental ΔR2* increased during maternal hyperoxia in healthy fetuses and fetuses with CHD, but it was higher in SV CHD (mean ΔR2*, 1.3 sec^-1 ± 0.1 [standard error; P < .01], 1.9 sec^-1 ± 0.2 [P < .01], and 1.0 sec^-1 ± 0.3 [P < .01], respectively, for control fetuses, fetuses with SV CHD, and fetuses with TV CHD). Placental ΔR2* during maternal hyperoxia changed with GA in healthy control fetuses and fetuses with SV or AO CHD (ΔR2* per week, 0.1 sec^-1 ± 0 [P < .01], 0.2 sec^-1 ± 0 [P = .01], and 0.2 sec^-1 ± 0 [P = .01], respectively), but not in fetuses with CHD and TV or non-AO. Fetal brain ΔR2* was constant across all phases in healthy control fetuses and fetuses with TV CHD but increased during maternal hyperoxia in fetuses with SV or AO CHD (mean ΔR2*, 0.7 sec^-1 ± 0.2 [P = .01] and 0.5 sec^-1 ± 0.2 [P = .02], respectively). Conclusion Six minutes of maternal hyperoxia increased placental oxygenation in healthy fetuses and fetuses with congenital heart disease, and it selectively increased cerebral blood oxygenation in fetuses with single ventricle or aortic obstruction. © RSNA, 2019 Online supplemental material is available for this article.

Placental MRI: Developing Accurate Quantitative Measures of Oxygenation

The Human Placenta Project has focused attention on the need for noninvasive magnetic resonance imaging (MRI)-based techniques to diagnose and monitor placental function throughout pregnancy. The hope is that the management of placenta-related pathologies would be improved if physicians had more direct, real-time measures of placental health to guide clinical decision making. As oxygen alters signal intensity on MRI and oxygen transport is a key function of the placenta, many of the MRI methods under development are focused on quantifying oxygen transport or oxygen content of the placenta. For example, measurements from blood oxygen level-dependent imaging of the placenta during maternal hyperoxia correspond to outcomes in twin pregnancies, suggesting that some aspects of placental oxygen transport can be monitored by MRI. Additional methods are being developed to accurately quantify baseline placental oxygenation by MRI relaxometry. However, direct validation of placental MRI methods is challenging and therefore animal studies and ex vivo studies of human placentas are needed. Here we provide an overview of the current state of the art of oxygen transport and quantification with MRI. We suggest that as these techniques are being developed, increased focus be placed on ensuring they are robust and reliable across individuals and standardized to enable predictive diagnostic models to be generated from the data. The field is still several years away from establishing the clinical benefit of monitoring placental function in real time with MRI, but the promise of individual personalized diagnosis and monitoring of placental disease in real time continues to motivate this effort.

Hyperoxygenation in pregnancy exerts a more profound effect on cardiovascular hemodynamics than is observed in the nonpregnant state

BACKGROUND

Supplemental oxygen is administered to pregnant women in many different clinical scenarios in obstetric practice. Despite the accepted uses for maternal hyperoxygenation, the impact of hyperoxia on maternal hemodynamic indices has not been evaluated. As a result, there is a paucity of data in the literature in relation to the physiological changes to the maternal circulation in response to supplemental oxygen.

OBJECTIVE

The hemodynamic effects of oxygen therapy are under-recognized and the impact of hyperoxygenation on maternal hemodynamics is currently unknown. Using noninvasive cardiac output monitoring which employs transthoracic bioreactance, we examined the effect of brief hyperoxygenation on cardiac index, systemic vascular resistance, blood pressure, stroke volume, and heart rate in pregnant mothers during the third trimester, compared with those effects observed in a nonpregnant population subjected to the same period of hyperoxygenation.

STUDY DESIGN

Hemodynamic monitoring was performed in a continuous manner over a 30-minute period using noninvasive cardiac output monitoring. Hyperoxygenation (O₂ 100% v/v inhalational gas) was carried out at a rate of 12 L/min via a partial non-rebreather mask for 10-minutes. Cardiac index, systemic vascular resistance, stroke volume, heart rate, and blood pressure were recorded before hyperoxygenation, at completion of hyperoxygenation, and 10 minutes after the cessation of hyperoxygenation. Two-way analysis of variance with repeated measures was used to assess the change in hemodynamic indices over time and the differences between the 2 groups.

RESULTS

Forty-six pregnant and 20 nonpregnant women with a median age of 33 years (interquartile range, 26-38 years) and 32 years (interquartile range, 28-37 years) were recruited prospectively, respectively (P=.82). The median gestational age was 35 weeks (33-37 weeks). In the pregnant group, there was a fall in cardiac index during the hyperoxygenation exposure period (P=.009) coupled with a rise in systemic vascular resistance with no recovery at 10 minutes after cessation of hyperoxygenation (P=.02). Heart rate decreased after hyperoxygenation exposure and returned to baseline by 10 minutes after cessation of therapy. There was a decrease in stroke volume over the exposure period, with no change in systolic or diastolic blood pressure. In the nonpregnant group, there was no significant change in the cardiac index, systemic vascular resistance, stroke volume, heart rate, or systolic or diastolic blood pressure during the course of exposure to hyperoxygenation.

CONCLUSION

Hyperoxygenation during the third trimester is associated with a fall in maternal cardiac index and a rise in systemic vascular resistance without recovery to baseline levels at 10 minutes after cessation of hyperoxygenation. The hemodynamic changes that were observed in this study in response to hyperoxygenation therapy during pregnancy could counteract any intended increase in oxygen delivery. The observed maternal effects of hyperoxygenation call for a reevaluation of the role of hyperoxygenation treatment in the nonhypoxemic pregnant patient.

Cerebrovascular response to maternal hyperoxygenation in fetuses with hypoplastic left heart syndrome depends on gestational age and baseline cerebrovascular resistance

OBJECTIVES

Compared with normal fetuses, fetuses with hypoplastic left heart syndrome (HLHS) have smaller brain volumes and are at higher risk of brain injury, possibly due to diminished cerebral blood flow and oxygen content. By increasing cerebral oxygen delivery, maternal hyperoxygenation (MH) might improve brain development and reduce the risk of brain injury in these fetuses. This study investigated whether gestational age and baseline cerebrovascular resistance affect the response to MH in fetuses with HLHS.

METHODS

The study population comprised 43 fetuses with HLHS or HLHS variant referred for fetal echocardiography between January 2004 and September 2008. Middle cerebral artery (MCA) pulsatility index (PI), a surrogate measure of cerebrovascular resistance, was assessed between 20 and 41 weeks' gestation at baseline in room air (RA) and after 10 min of MH. Z-scores of MCA-PI were generated. A mixed-effects model was used to determine whether change in MCA-PI depends upon gestational age and baseline MCA-PI.

RESULTS

In RA and following MH, MCA-PI demonstrated a curvilinear relationship with gestational age in fetuses with HLHS, peaking at around 28 weeks and then falling more steeply near term. MCA-PI Z-score declined in a linear manner, such that it was 1.4 SD below that in normal fetuses at 38 weeks. Increase in MCA-PI Z-score after MH was first seen at ≥ 28 weeks. A baseline MCA-PI Z-score ≤ -0.96 was predictive of an increase in cerebrovascular resistance in response to MH.

CONCLUSION

In fetuses with HLHS, MCA-PI first increases in response to MH at ≥ 28 weeks' gestation. A baseline MCA-PI Z-score ≤ -0.96 predicts an increase in cerebrovascular resistance in response to MH. These results may have implications for clinical trials utilizing MH as a neuroprotective agent. Copyright © 2017 ISUOG. Published by John Wiley & Sons Ltd.

In Vivo Quantification of Placental Insufficiency by BOLD MRI: A Human Study

Fetal health is critically dependent on placental function, especially placental transport of oxygen from mother to fetus. When fetal growth is compromised, placental insufficiency must be distinguished from modest genetic growth potential. If placental insufficiency is present, the physician must trade off the risk of prolonged fetal exposure to placental insufficiency against the risks of preterm delivery. Current ultrasound methods to evaluate the placenta are indirect and insensitive. We propose to use Blood-Oxygenation-Level-Dependent (BOLD) MRI with maternal hyperoxia to quantitatively assess mismatch in placental function in seven monozygotic twin pairs naturally matched for genetic growth potential. In-utero BOLD MRI time series were acquired at 29 to 34 weeks gestational age. Maps of oxygen Time-To-Plateau (TTP) were obtained in the placentas by voxel-wise fitting of the time series. Fetal brain and liver volumes were measured based on structural MR images. After delivery, birth weights were obtained and placental pathological evaluations were performed. Mean placental TTP negatively correlated with fetal liver and brain volumes at the time of MRI as well as with birth weights. Mean placental TTP positively correlated with placental pathology. This study demonstrates the potential of BOLD MRI with maternal hyperoxia to quantify regional placental function in vivo.

The impact of maternal hyper-oxygenation on foeto-placental blood flow

OBJECTIVE

Maternal hyperoxygenation has been reported to increase foetal oxygen saturation, and is frequently employed during intra-partum episodes of foetal compromise as a component of in utero resuscitation. However, there has been little investigation of its influence on foetal haemodynamics, particularly in appropriately grown foetuses.

METHODS

This cohort study was undertaken between July 2013 and November 2013. All participants underwent an ultrasound scan prior to active labour (<4 cm dilated), during which foetal biometry, umbilical and middle cerebral artery Dopplers were recorded. Doppler measurements were then repeated after a 20-min period (to act as a control for subsequent measurements after oxygen therapy). Women were then asked to breathe 60% oxygen through Venturi valve masks for 20 min, after which the Doppler measurements were repeated.

RESULTS

Twenty women were recruited to the study. No significant change in the foetal cerebro-umbilical (CU) ratio was observed following maternal oxygen therapy. The degree of change in Doppler parameters after oxygen therapy was not related to the baseline value of the Doppler parameter.

CONCLUSION

Maternal hyperoxygenation using 60% oxygen concentration over a 20-min period does not influence foetal umbilical or middle cerebral artery Doppler in appropriately grown foetuses. No adverse effects of maternal oxygen therapy were observed.

Changes in human fetal oxygenation during maternal hyperoxia as estimated by BOLD MRI

OBJECTIVE

Changes in blood oxygen level dependent (BOLD) magnetic resonance imaging (MRI) signal are closely related to changes in fetal oxygenation. In this study, we aimed to investigate the changes in human fetal oxygenation during maternal hyperoxia by using the non-invasive BOLD MRI technique.

METHOD

Eight healthy pregnant women in gestational week 28 to 34 were included. With the use of a facial oxygen mask, we induced maternal hyperoxia and measured changes in the BOLD MRI signal of selected fetal organs.

RESULTS

In a number of fetal organs, the BOLD MRI signal increased significantly (P < 0.01) during maternal hyperoxia (mean change in % ± SEM): liver (14.3 ± 3.7%), spleen (15.2 ± 3.5%) and kidney (6.2 ± 1.8%) as well as the placenta (6.5 ± 1.6%). In the fetal brain, however, the BOLD MRI signal remained constant (0.3 ± 0.2%).

CONCLUSION

During maternal hyperoxia, we demonstrated an increased oxygenation in a number of human fetal organs by using the non-invasive BOLD technique. The oxygenation of the fetal brain remained constant, thus a 'reversed' brain sparing mechanism could be considered in healthy fetuses subjected to hyperoxia.

Fetal growth restriction - from observation to intervention

Fetal growth restriction (FGR) due to placental dysfunction has important short- and long-term impacts that may reach into adulthood. Early-onset FGR before 34 weeks' gestation shows a characteristic sequence of responses to placental dysfunction that evolves from the arterial circulation to the venous system and finally to biophysical abnormalities. In this form of FGR safe prolongation of pregnancy is a primary management goal, as gestational age at delivery, birth weight and iatrogenic premature delivery have an important impact on short-term outcome and neurodevelopment. Surveillance intervals should be adjusted based on umbilical artery and venous Doppler studies. Intervention thresholds need to be based on the balance of fetal vs. neonatal risks and therefore critically depend on gestational age. Late-onset FGR presents with subtle Doppler and biophysical abnormalities and therefore poses a diagnostic dilemma. Often unrecognized, term FGR contributes to a large proportion of adverse perinatal outcome. Monitoring intervals should be adjusted based on middle cerebral artery Doppler and fetal heart rate parameters. Delivery timing thresholds can be low. In both forms of FGR neurodevelopmental impacts of placental disease occur before clinical decisions regarding delivery timing arise. This places special emphasis on future preventative studies.

Reducing stillbirths: interventions during labour

BACKGROUND

Approximately one million stillbirths occur annually during labour; most of these stillbirths occur in low and middle-income countries and are associated with absent, inadequate, or delayed obstetric care. The low proportion of intrapartum stillbirths in high-income countries suggests that intrapartum stillbirths are largely preventable with quality intrapartum care, including prompt recognition and management of intrapartum complications. The evidence for impact of intrapartum interventions on stillbirth and perinatal mortality outcomes has not yet been systematically examined.

METHODS

We undertook a systematic review of the published literature, searching PubMed and the Cochrane Library, of trials and reviews (N = 230) that reported stillbirth or perinatal mortality outcomes for eight interventions delivered during labour. Where eligible randomised controlled trials had been published after the most recent Cochrane review on any given intervention, we incorporated these new trial findings into a new meta-analysis with the Cochrane included studies.

RESULTS

We found a paucity of studies reporting statistically significant evidence of impact on perinatal mortality, especially on stillbirths. Available evidence suggests that operative delivery, especially Caesarean section, contributes to decreased stillbirth rates. Induction of labour rather than expectant management in post-term pregnancies showed strong evidence of impact, though there was not enough evidence to suggest superior safety for the fetus of any given drug or drugs for induction of labour. Planned Caesarean section for term breech presentation has been shown in a large randomised trial to reduce stillbirths, but the feasibility and consequences of implementing this intervention routinely in low-/middle-income countries add caveats to recommending its use. Magnesium sulphate for pre-eclampsia and eclampsia is effective in preventing eclamptic seizures, but studies have not demonstrated impact on perinatal mortality. There was limited evidence of impact for maternal hyperoxygenation, and concerns remain about maternal safety. Transcervical amnioinfusion for meconium staining appears promising for low/middle income-country application according to the findings of many small studies, but a large randomised trial of the intervention had no significant impact on perinatal mortality, suggesting that further studies are needed.

CONCLUSION

Although the global appeal to prioritise access to emergency obstetric care, especially vacuum extraction and Caesarean section, rests largely on observational and population-based data, these interventions are clearly life-saving in many cases of fetal compromise. Safe, comprehensive essential and emergency obstetric care is particularly needed, and can make the greatest impact on stillbirth rates, in low-resource settings. Other advanced interventions such as amnioinfusion and hyperoxygenation may reduce perinatal mortality, but concerns about safety and effectiveness require further study before they can be routinely included in programs.

Where the O2 goes to: preservation of human fetal oxygen delivery and consumption at high altitude

Fetal growth is decreased at high altitude (> 2700 m). We hypothesized that variation in fetal O(2) delivery might account for both the altitude effect and the relative preservation of fetal growth in multigenerational natives to high altitude. Participants were 168 women of European or Andean ancestry living at 3600 m or 400 m. Ancestry was genetically confirmed. Umbilical vein blood flow was measured using ultrasound and Doppler. Cord blood samples permitted calculation of fetal O(2) delivery and consumption. Andean fetuses had greater blood flow and oxygen delivery than Europeans and weighed more at birth, regardless of altitude (+208 g, P < 0.0001). Fetal blood flow was decreased at 3600 m (P < 0.0001); the decrement was similar in both ancestry groups. Altitude-associated decrease in birth weight was greater in Europeans (-417 g) than Andeans (-228 g, P < 0.005). Birth weight at 3600 m was > 200 g lower for Europeans at any given level of blood flow or O(2) delivery. Fetal haemoglobin concentration was increased, decreased, and the fetal / curve was left-shifted at 3600 m. Fetuses receiving less O(2) extracted more (r(2) = 0.35, P < 0.0001). These adaptations resulted in similar fetal O(2) delivery and consumption across all four groups. Increased umbilical venous O(2) delivery correlated with increased fetal O(2) consumption per kg weight (r(2) = 0.50, P < 0.0001). Blood flow (r(2) = 0.16, P < 0.001) and O(2) delivery (r(2) = 0.17, P < 0.001) correlated with birth weight at 3600 m, but not at 400 m (r(2) = 0.04, and 0.03, respectively). We concluded that the most pronounced difference at high altitude is reduced fetal blood flow, but fetal haematological adaptation and fetal capacity to increase O(2) extraction indicates that deficit in fetal oxygen delivery is unlikely to be causally associated with the altitude- and ancestry-related differences in fetal growth.

Intrauterine resuscitation during labor: should maternal oxygen administration be a first-line measure?

Intrauterine resuscitation techniques are often used during labor when the fetal heart rate pattern is nonreassuring. These techniques have not been well studied; common practices are based on classic studies many years old. Models of intrauterine resuscitation using one (or more) technique as a first-line intervention and adding others in a specific series or clinical algorithm based on fetal response have not been tested. Maternal oxygen therapy is often used; however, recent evidence suggests potential risks to the mother and fetus or newborn. Even small increases in maternal and fetal pO(2) as a result of maternal oxygen administration can produce oxygen free radical activity in mothers and fetuses. The potential long-term effects are unknown. Caution should be exercised when considering maternal oxygen administration as a first-line intrauterine resuscitation measure until more data are available, reserving its use after other measures have been unsuccessful in resolving the nonreassuring fetal heart rate pattern.