Absence of neuronal damage after umbilical cord occlusion of 10, 15, and 20 minutes in midgestation fetal sheep

Assessment of extremely premature lambs supported by the Extrauterine Environment for Neonatal Development (EXTEND)

BACKGROUND

Our team has previously reported physiologic support by the EXTra-uterine Environment for Neonatal Development (EXTEND) of 105 to 117 days gestational age (GA) lambs for up to 28 days with normal organ maturation. However, the fetal lamb brain matures more rapidly, requiring the study of 90-105 day GA fetal lambs to assess more neurodevelopmentally equivalent lambs to the 23-25 week GA extreme premature infant.

METHODS

Extremely preterm lambs (90-95 days of GA) were delivered by C-section and supported by EXTEND. Estimated circuit flows were maintained at around 325 ml/kg/min. After support on EXTEND, MRI and histopathologic analysis were performed and compared to 105-112 days GA control lambs.

RESULTS

The extremely preterm group includes 10 animals with a mean GA of 91.6 days, a mean weight at cannulation of 0.98 kg and a mean length of stay on EXTEND of 13.5 days (10-21 days). Hemodynamics and oxygenation showed stable parameters. Animals showed growth and physiologic cardiac function. MRI volumetric and diffusion analysis was comparable to controls. Histologic brain analysis revealed no difference between study groups.

CONCLUSION

EXTEND appears to support brain and cardiac development in an earlier gestation, less mature, lamb model.

IMPACT

Prolonged (up to 21 days) physiological support of extremely preterm lambs of closer neurodevelopmental equivalence to the 24-28 gestational week human was achieved using the EXTEND system. EXTEND treatment supported brain growth and development in extremely preterm fetal lambs and was not associated with intraventricular hemorrhage or white matter injury. Daily echocardiography demonstrated physiologic heart function, absence of cardiac afterload, and normal developmental increase in cardiac chamber dimensions. This study demonstrates hemodynamic and metabolic support by the EXTEND system in the extremely preterm ovine model.

Maternal nutrient restriction in guinea pigs leads to fetal growth restriction with increased brain apoptosis

BACKGROUND

We determined whether maternal nutrient restriction (MNR) in guinea pigs leading to fetal growth restriction (FGR) impacts cell death in the brain with implications for neurodevelopmental adversity.

METHODS

Guinea pigs were fed ad libitum (Control) or 70% of the control diet before pregnancy, switching to 90% at mid-pregnancy (MNR). Fetuses were necropsied near term and brain tissues processed for necrosis (H&E), apoptosis (TUNEL), and pro- (Bax) and anti- (Bcl-2 and Grp78) apoptotic protein immunoreactivity.

RESULTS

FGR-MNR fetal and brain weights were decreased 38% and 12%, respectively, indicating brain sparing but with brains still smaller. While necrosis remained unchanged, apoptosis was increased in the white matter and hippocampus in the FGR brains, and control and FGR-related apoptosis were increased in males for most brain areas. Bax was increased in the CA4 and Bcl-2 was decreased in the dentate gyrus in the FGR brains supporting a role in the increased apoptosis, while Grp78 was increased in the FGR females, possibly contributing to the sex-related differences.

CONCLUSIONS

MNR-induced FGR results in increased brain apoptosis with regional and sex-related differences that may contribute to the reduction in brain area size reported clinically and increased risk in FGR males for later neurodevelopmental adversity.

Neurobehavioural outcome in 6-18 year old children after trauma in pregnancy: Case-control study

BACKGROUND

Maternal trauma complicates pregnancy in approximately 7%. Long-term development of children exposed to maternal trauma is unknown.

AIM

To determine neurobehavioural outcome of children (6-18 years) born after maternal trauma in pregnancy compared to a matched control group.

STUDY DESIGN

Case-control study performed at a tertiary medical centre.

SUBJECTS

All consecutive children born after maternal hospitalization for trauma during pregnancy between 1995 and 2005. Controls were children born at the same hospital and period after an uneventful pregnancy.

OUTCOME MEASURES

Trauma type and severity (Injury Severity Score, ≥9: severe); information from medical files at admission (cases). All mothers filled out two questionnaires about the infant; 1. concerning health, motor development and educational level, 2. concerning behavioural development through the validated Dutch version of the Child Behavior Checklist (CBCL).

RESULTS

Questionnaires were returned by 34 cases and 28 controls. The traumas concerned mainly motor vehicle accidents and falls, and 3/34 had severe injuries. No differences in health, motor development, educational level and CBCL was found between the cases and controls, except for more hospitalization in the cases (p = 0.009).

CONCLUSION

Long-term follow-up of a limited population of children 6-18 years after exposure of mainly non-severe trauma before birth is similar to a control population except for unexplained more hospitalization in the cases.

The fetus at the tipping point: modifying the outcome of fetal asphyxia

Brain injury around birth is associated with nearly half of all cases of cerebral palsy. Although brain injury is multifactorial, particularly after preterm birth, acute hypoxia-ischaemia is a major contributor to injury. It is now well established that the severity of injury after hypoxia-ischaemia is determined by a dynamic balance between injurious and protective processes. In addition, mothers who are at risk of premature delivery have high rates of diabetes and antepartum infection/inflammation and are almost universally given treatments such as antenatal glucocorticoids and magnesium sulphate to reduce the risk of death and complications after preterm birth. We review evidence that these common factors affect responses to fetal asphyxia, often in unexpected ways. For example, glucocorticoid exposure dramatically increases delayed cell loss after acute hypoxia-ischaemia, largely through secondary hyperglycaemia. This critical new information is important to understand the effects of clinical treatments of women whose fetuses are at risk of perinatal asphyxia.

Hypoxia-ischemia is not an antecedent of most preterm brain damage: the illusion of validity

Brain injury in preterm newborn infants is often attributed to hypoxia-ischemia even when neither hypoxia nor ischemia is documented, and many causative speculations are based on the same assumption. We review human and animal study contributions with their strengths and limitations, and conclude that - despite all the work done in human fetal neuropathology and developmental models in animals - the evidence remains unconvincing that hypoxemia, in the fetus or newborn infant, contributes appreciably to any encephalopathy of prematurity. Giving an inappropriate causal name to a disorder potentially limits the options for change, should our understanding of the etiologies advance. The only observationally-based title we think appropriate is 'encephalopathy of prematurity'. Future pathophysiological research should probably include appropriately designed epidemiology studies, highly active developmental processes, infection and other inflammatory stimuli, the immature immune system, long chain fatty acids and their transporters, and growth (neurotrophic) factors.

WHAT THIS PAPER ADDS

Fetal hypoxemia is rarely documented in brain injury studies. Animal studies fail to consider human-animal fetal anatomical differences. Putative treatments from animal models have not found clinical use. Observational studies constitute the only approach to etiological understanding. No convincing evidence yet that hypoxemia injures preterm brain. Encephalopathy of prematurity is preferable to hypoxia-ischemia as a term for this disorder. Encephalopathy of prematurity is preferable to hypoxia-ischemia as a term for this disorder.

Animal welfare aspects in respect of the slaughter or killing of pregnant livestock animals (cattle, pigs, sheep, goats, horses)

This scientific opinion addresses animal welfare aspects of slaughtering of livestock pregnant animals. Term of Reference (ToR) 1 requested assessment of the prevalence of animals slaughtered in a critical developmental stage of gestation when the livestock fetuses might experience negative affect. Limited data on European prevalence and related uncertainties necessitated a structured expert knowledge elicitation (EKE) exercise. Estimated median percentages of animals slaughtered in the last third of gestation are 3%, 1.5%, 0.5%, 0.8% and 0.2% (dairy cows, beef cattle, pigs, sheep and goats, respectively). Pregnant animals may be sent for slaughter for health, welfare, management and economic reasons (ToR2); there are also reasons for farmers not knowing that animals sent for slaughter are pregnant. Measures to reduce the incidence are listed. ToR3 asked whether livestock fetuses can experience pain and other negative affect. The available literature was reviewed and, at a second multidisciplinary EKE meeting, judgements and uncertainty were elicited. It is concluded that livestock fetuses in the last third of gestation have the anatomical and neurophysiological structures required to experience negative affect (with 90-100% likelihood). However, there are two different possibilities whether they perceive negative affect. It is more probable that the neurophysiological situation does not allow for conscious perception (with 66-99% likelihood) because of brain inhibitory mechanisms. There is also a less probable situation that livestock fetuses can experience negative affect (with 1-33% likelihood) arising from differences in the interpretation of the fetal electroencephalogram, observed responses to external stimuli and the possibility of fetal learning. Regarding methods to stun and kill livestock fetuses at slaughter (ToR4), sets of scenarios and respective actions take account of both the probable and less probable situation regarding fetal ability for conscious perception. Finally, information was collated on methods to establish the dam's gestational stage based on physical features of livestock fetuses (ToR5).

Sex, drugs and rock and roll: tales from preterm fetal life

Premature fetuses and babies are at greater risk of mortality and morbidity than their term counterparts. The underlying causes are multifactorial, but include exposure to hypoxia. Immaturity of organs and their functional control may impair the physiological defence responses to hypoxia and the preterm fetal responses, or lack thereof, to moderate hypoxia appear to support this concept. However, as this review demonstrates, despite immaturity, the preterm fetus responds to asphyxia in a qualitatively similar manner to that seen at term. This highlights the importance in understanding metabolism versus homeostatic threat when assessing fetal responses to adverse challenges such as hypoxia. Data are presented to show that the preterm fetal adaptation to asphyxia is triphasic in nature. Phase one represents the rapid institution of maximal defences, designed to maintain blood pressure and central perfusion at the expense of peripheral organs. Phase two is one of adaptive compensation. Controlled reperfusion partially offsets peripheral tissue oxygen debt, while maintaining sufficient vasoconstriction to limit the fall in perfusion. Phase three is about decompensation. Strikingly, the preterm fetus generally performs better during phases two and three, and can survive for longer without injury. Paradoxically, however, the ability to survive can lead to longer exposure to hypotension and hypoperfusion and thus potentially greater injury. The effects of fetal sex, inflammation and drugs on the triphasic adaptations are reviewed. Finally, the review highlights the need for more comprehensive studies to understand the complexity of perinatal physiology if we are to develop effective strategies to improve preterm outcomes.

Effects of Umbilical Cord Occlusion in Late Gestation on the Ovine Fetal Brain and Retina

OBJECTIVE

Previous studies on the effects of umbilical cord occlusion (UCO) on the fetal brain have focused on short-term alterations, and in most cases have used only subjective techniques to evaluate brain injury. Our aim was to assess quantitatively the persistent consequences of UCO on the developing brain; we also examined the retina.

METHODS

We subjected fetal sheep to a single episode of UCO at 126 days of gestation (term approximately 147 days) to induce at least 10 minutes of isoelectric fetal electrocorticogram (ECoG).

RESULTS

UCO resulted in fetal asphyxia and transient mild alterations in fetal mean arterial pressure (MAP). UCO did not result in significant injury to the developing brain or retina when assessed 15 days after the insult. There was no change in the endogenous expression of brain-derived neurotrophic factor (BDNF) protein in the hippocampus, nor was there a significant loss of CA1 hippocampal pyramidal cells. However, this insult did result in subtle neuropathologic alterations in the brain, including a reduction in the weight of the cerebral hemispheres, an increase in the areal density of cerebellar Purkinje cells, and enlarged perivascular spaces around blood vessels and inflammatory cells in the cerebral white matter. UCO did not affect the thickness of the central or peripheral retina or the numbers of retinal dopaminergic, cholinergic, and nitrergic amacrine cells.

CONCLUSIONS

Thus, while 10 minutes of UCO did not result in overt injury to the fetal brain or retina, the observed changes in the fetal brain suggest altered growth of neural processes, which may contribute to neurologic deficits postnatally or to increased vulnerability of the brain to later insults during either the remainder of gestation or after birth.

Vulnerability of the developing brain to hypoxic-ischemic damage: contribution of the cerebral vasculature to injury and repair?

As clinicians attempt to understand the underlying reasons for the vulnerability of different regions of the developing brain to injury, it is apparent that little is known as to how hypoxia-ischemia may affect the cerebrovasculature in the developing infant. Most of the research investigating the pathogenesis of perinatal brain injury following hypoxia-ischemia has focused on excitotoxicity, oxidative stress and an inflammatory response, with the response of the developing cerebrovasculature receiving less attention. This is surprising as the presentation of devastating and permanent injury such as germinal matrix-intraventricular haemorrhage (GM-IVH) and perinatal stroke are of vascular origin, and the origin of periventricular leukomalacia (PVL) may also arise from poor perfusion of the white matter. This highlights that cerebrovasculature injury following hypoxia could primarily be responsible for the injury seen in the brain of many infants diagnosed with hypoxic-ischemic encephalopathy (HIE). Interestingly the highly dynamic nature of the cerebral blood vessels in the fetus, and the fluctuations of cerebral blood flow and metabolic demand that occur following hypoxia suggest that the response of blood vessels could explain both regional protection and vulnerability in the developing brain. However, research into how blood vessels respond following hypoxia-ischemia have mostly been conducted in adult models of ischemia or stroke, further highlighting the need to investigate how the developing cerebrovasculature responds and the possible contribution to perinatal brain injury following hypoxia. This review discusses the current concepts on the pathogenesis of perinatal brain injury, the development of the fetal cerebrovasculature and the blood brain barrier (BBB), and key mediators involved with the response of cerebral blood vessels to hypoxia.

Intrauterine fetal demise can be remote from the inciting insult in an animal model of hypoxia-ischemia

BACKGROUND

Fetal hypoxia-ischemia (H-I) results in significant morbidity and mortality. Little is known about the timing of death in human stillbirths. The vulnerability of the fetus varies with age at the time of insult, but it is unknown what happens to the timing of fetal death in relation to a fetal insult. We asked the question of whether the timing of fetal death was influenced by the age at which the insult occurred.

METHODS

Fetal H-I was achieved at three ages by sustained uterine ischemia in rabbits, mimicking the acute placental insufficiency of placental abruption.

RESULTS

H-I at 22 d gestation (E22) resulted in fewer perinatal deaths than at E25 and E29. Fetal deaths were grouped into early and late perinatal deaths. Early perinatal death mostly occurred immediately after H-I and these fetuses delivered before term. Late perinatal death occurred between the insult and delivery at term gestation. Early perinatal death occurred more often in the E25 hypoxic-ischemic group as compared with those of the E22 hypoxic-ischemic group.

CONCLUSION

There is an increasing vulnerability to hypoxia with increasing gestational age. Perinatal deaths may occur long after the episode of H-I. The timing of an intrauterine hypoxic-ischemic event cannot be inferred from the detection of fetal death.

Maturation of the mitochondrial redox response to profound asphyxia in fetal sheep

Fetal susceptibility to hypoxic brain injury increases over the last third of gestation. This study examined the hypothesis that this is associated with impaired mitochondrial adaptation, as measured by more rapid oxidation of cytochrome oxidase (CytOx) during profound asphyxia. Methods: Chronically instrumented fetal sheep at 0.6, 0.7, and 0.85 gestation were subjected to either 30 min (0.6 gestational age (ga), n = 6), 25 min (0.7 ga, n = 27) or 15 min (0.85 ga, n = 17) of complete umbilical cord occlusion. Fetal EEG, cerebral impedance (to measure brain swelling) and near-infrared spectroscopy-derived intra-cerebral oxygenation (ΔHb = HbO₂ – Hb), total hemoglobin (THb) and CytOx redox state were monitored continuously. Occlusion was associated with profound, rapid fall in ΔHb in all groups to a plateau from 6 min, greatest at 0.85 ga compared to 0.6 and 0.7 ga (p<0.05). THb initially increased at all ages, with the greatest rise at 0.85 ga (p<0.05), followed by a progressive fall from 7 min in all groups. CytOx initially increased in all groups with the greatest rise at 0.85 ga (p<0.05), followed by a further, delayed increase in preterm fetuses, but a striking fall in the 0.85 group after 6 min of occlusion. Cerebral impedance (a measure of cytotoxic edema) increased earlier and more rapidly with greater gestation. In conclusion, the more rapid rise in CytOx and cortical impedance during profound asphyxia with greater maturation is consistent with increasing dependence on oxidative metabolism leading to earlier onset of neural energy failure before the onset of systemic hypotension.

Non-immune hydrops fetalis: a short review of etiology and pathophysiology

Hydrops fetalis is an excessive accumulation of fetal fluid. Hydrops is traditionally classified into either immune or non-immune hydrops (NIHF), but in practice, nowadays in the Western world >90% of hydrops is of non-immune origin. The basis of the disorder is an imbalance in the regulation of fetal fluid movement between the vascular and interstitial space. We previously suggested a diagnostic flow-chart for NIHF. In this short review we describe the main mechanisms leading to NIHF.

Early Cerebral Hemodynamic, Metabolic, and Histological Changes in Hypoxic-Ischemic Fetal Lambs during Postnatal Life

The hemodynamic, metabolic, and biochemical changes produced during the transition from fetal to neonatal life may be aggravated if an episode of asphyxia occurs during fetal life. The aim of the study was to examine regional cerebral blood flow (RCBF), histological changes, and cerebral brain metabolism in preterm lambs, and to analyze the role of oxidative stress in the first hours of postnatal life following severe fetal asphyxia. Eighteen chronically instrumented newborn lambs were randomly assigned to either a control group or the hypoxic-ischemic (HI) group, in which case fetal asphyxia was induced just before delivery. All the animals were maintained on intermittent positive pressure ventilation for 3 h after delivery. During the HI insult, the injured group developed acidosis, hypoxia, hypercapnia, lactic acidosis, and tachycardia (relative to the control group), without hypotension. The intermittent positive pressure ventilation transiently improved gas exchange and cardiovascular parameters. After HI injury and during ventilatory support, there continued to be an increased RCBF in inner regions among the HI group, but no significant differences were detected in cortical flow compared to the control group. Also, the magnitude of the increase in TUNEL positive cells (apoptosis) and antioxidant enzymes, and decrease of ATP reserves was significantly greater in the brain regions where the RCBF was not higher. In conclusion, our findings identify early metabolic, histological, and hemodynamic changes involved in brain damage in premature asphyxiated lambs. Such changes have been described in human neonates, so our model could be useful to test the safety and the effectiveness of different neuroprotective or ventilation strategies applied in the first hours after fetal HI injury.

Fetal hypoxia insults and patterns of brain injury: insights from animal models

The outcome of perinatal hypoxiaischemia is highly variable, with only a very broad relationship to the 'severity' of oxygen debt as shown by peripheral base deficit and the risk of damage. The present article examines the pathophysiology of asphyxial injury. We dissect the multiple factors that modify the risk of injury, including the depth ('severity'), duration, and repetition of the insult, the maturity, and condition of the fetus, pre-existing hypoxia, and exposure to pyrexia and infection/inflammation.

Predictors of umbilical artery acidosis in preterm delivery

OBJECTIVE

The purpose of this study was to investigate the significance of preterm acidosis and its risk factors.

STUDY DESIGN

From a cohort of 786 consecutive singleton neonates who were born after spontaneous or iatrogenic preterm delivery at 24.0-33.6 weeks of gestation from January 1993 to December 2005 with an evaluation of umbilical artery pH at delivery, we extracted demographic, obstetric, neonatal, and placental histologic variables and related them to umbilical artery evidence of fetal acidemia, which was defined as pH <7.10. Excluded were stillbirths and neonates with major congenital anomalies. Fetal distress was defined as nonreassuring fetal hearth rate tracing or biophysical profile or appearance of thick meconium at delivery. Statistical analysis included 1-way analysis of variance and logistic regression with a probability value of <.05 considered significant.

RESULTS

Neonates with umbilical cord evidence of acidosis (n = 34) were born more frequently after abruption (P < .001), fetal distress (P < .001), and by cesarean delivery (P < .04) and were born less frequently after a complete course of corticosteroids (P = .03) and labor (P = .05) than nonacidotic babies (n = 752). Acute inflammatory lesions at placental histologic evaluation were less frequent (P = .049), and placental vascular lesions were more common in acidotic than in nonacidotic preterm neonates (P = .039). Logistic regression analysis demonstrated that cord acidosis was associated independently with the occurrence of abruptio placentae (odds ratio, 7.3; 95% CI, 2.9, 18.8), fetal distress (odds ratio, 12.0; 95% CI, 4.9, 18.3), and vascular placental lesions (odds ratio, 2.8; 95% CI, 1.2, 6.8)

CONCLUSION

In preterm infants, umbilical artery acidosis is significantly more common in the presence of placental abruption, fetal distress, and histologic evidence of placental vascular disease.

Male disadvantage? Fetal sex and cardiovascular responses to asphyxia in preterm fetal sheep

Clinically and experimentally male fetuses are at significantly greater risk of dying or suffering injury at birth, particularly after premature delivery. We undertook a retrospective cohort analysis of 60 female and 65 male singleton preterm fetal sheep (103–104 days, 0.7 gestation) with mean arterial blood pressure (MAP), heart rate, and carotid and femoral blood flow recordings during 25 min of umbilical cord occlusion in utero. Occlusions were stopped early if fetal MAP fell below 8 mmHg or if there was asystole for >20 s. Fetuses that were able to complete the full 25-min period of occlusion showed no differences between sexes for any cardiovascular responses. Similar numbers of occlusions were stopped early in males (mean: 21 min, n = 16) and females (mean: 23 min, n = 16); however, they showed different responses. Short-occlusion males ( n = 16) showed a slower initial fall in femoral vascular conductance, followed by greater bradycardia, hypotension, and associated organ hypoperfusion compared with full-occlusion fetuses. In contrast, short-occlusion females ( n = 16) showed a significantly more rapid early increase in femoral vascular conductance than the full-occlusion fetuses, followed by worsening of bradycardia and hypotension that was intermediate to the full-occlusion fetuses and short-occlusion males. Among all fetuses, MAP at 15 min of occlusion, corresponding with the time of the maximal rate of fall, was correlated with postmortem weight in males ( R2 = 0.07) but not females. In conclusion, male and female fetuses showed remarkably similar chemoreflex and hemodynamic responses to severe asphyxia, but some males did show impaired hemodynamic adaptation within the normal weight range.

The ontogeny of hemodynamic responses to prolonged umbilical cord occlusion in fetal sheep

There is evidence that preterm fetuses have blunted chemoreflex-mediated responses to hypoxia. However, the preterm fetus has much lower aerobic requirements than at term, and so moderate hypoxia may not be sufficient to elicit maximal chemoreflex responses; there are only limited quantitative data on the ontogeny of chemoreflex and hemodynamic responses to severe asphyxia. Chronically instrumented fetal sheep at 0.6 (n = 12), 0.7 (n = 12), and 0.85 (n = 8) of gestational age (GA; term = 147 days) were exposed to 30, 25, or 15 min of complete umbilical cord occlusion, respectively. At all ages, occlusion was associated with early onset of bradycardia, profoundly reduced femoral blood flow and conductance, and hypertension. The 0.6-GA fetuses showed a significantly slower and lesser fall in femoral blood flow and conductance compared with the 0.85-GA group, with a correspondingly reduced relative rise in mean arterial blood pressure. As occlusion continued, the initial adaptation was followed by loss of peripheral vasoconstriction and progressive development of hypotension in all groups. The 0.85-GA fetuses showed significantly more sustained reduction in femoral conductance but also more rapid onset of hypotension than either of the younger groups. Electroencephalographic (EEG) activity was suppressed during occlusion in all groups, but the degree of suppression was less at 0.6 GA than at term. In conclusion, the near-midgestation fetus shows attenuated initial (chemoreflex) peripheral vasomotor responses to severe asphyxia compared with more mature fetuses but more sustained hemodynamic adaptation and reduced suppression of EEG activity during continued occlusion of the umbilical cord.

Regulation of cytochrome oxidase redox state during umbilical cord occlusion in preterm fetal sheep

The preterm fetus is capable of surviving prolonged periods of severe hypoxia without neural injury for much longer than at term. To evaluate the hypothesis that regulated suppression of brain metabolism contributes to this remarkable tolerance, we assessed changes in the redox state of cytochrome oxidase (CytOx) relative to cerebral heat production, and cytotoxic edema measured using cerebral impedance, during 25 min of complete umbilical cord occlusion or sham occlusion in fetal sheep at 0.7 gestation. Occlusion was followed by rapid, profound reduction in relative cerebral oxygenation and EEG intensity and an immediate increase in oxidized CytOx, indicating a reduction in electron flow down the mitochondrial electron transfer chain. Confirming rapid suppression of cerebral metabolism there was a loss of the temperature difference between parietal cortex and body at a time when carotid blood flow was maintained at control values. As occlusion continued, severe hypotension/hypoperfusion developed, with a further increase in CytOx levels to a plateau between 8 and 13 min and a progressive rise in cerebral impedance. In conclusion, these data strongly suggest active regulation of cerebral metabolism during the initial response to severe hypoxia, which may help to protect the immature brain from injury.

The Current Crisis in Obstetrics

Of the issues leading to legal actions in obstetrics, the most important are events occurring before delivery that are deemed to account for the birth of a physically or mentally challenged child. In determining causation in the clinical setting, the diagnosis of fetal asphyxia can be made using blood gas and acid-base assessment. However, there are many subsidiary questions that in most cases cannot be answered, including when the asphyxia began, the severity and nature of the asphyxia during the exposure, the quality of the cardiovascular compensation, and when the brain damage occurred. When scientific proof is not available, the dilemma for the court is the requirement to reach a conclusion about the timing of brain damage on the balance of probabilities. Although it is of value, clinical risk scoring using fetal heart rate (FHR) monitoring may result in false positive predictions of fetal asphyxia. The problem in FHR monitoring is the lack of a detailed algorithm for the interpretation of FHR patterns with appropriate recommendations for management. Until such an algorithm is developed, health care workers cannot be expected to respond to fetal heart rate patterns consistently. Responsibility for the crisis in obstetrics must rest with the members of the health care disciplines who provide expert testimony. Progress made in research encourages us to assume that more is known about the causes of brain damage in the clinical setting than in fact is known. Similarly, health care professionals, parents, and lawyers often assume current methods of prediction and diagnosis to be more effective than they actually are.

Severe umbilical cord acidemia and neurological outcome in preterm and full-term neonates

BACKGROUND

Severe intrauterine hypoxia-ischemia and acidemia may lead to a disturbed neurodevelopment.

OBJECTIVES

To study the effects of acidemia at birth on neurodevelopment in preterm and full-term neonates.

SUBJECTS AND METHODS

Short- and long-term outcome were studied retrospectively in 44 inborn preterms and 95 full-terms with severe acidemia at birth defined as a pH of the umbilical artery <7.00. Outcome was compared with 67 preterm and 90 full-term non-acidemic neonates (pH>7.15). Intraventricular hemorrhage (preterms) or seizures (both preterms and full-terms) were considered an adverse short-term outcome. Neonatal death, cerebral palsy or neurodevelopmental delay were considered an adverse long-term outcome.

RESULTS

Severe intraventricular hemorrhage (IVH) occurred in 5 of the 44 (11%) acidemic preterms and in none of the 67 (0%) non-acidemic preterms (p<0.01). Seizures were observed in 9 of the 44 (20%) and 11 of the 95 (12%) acidemic preterms and full-terms, respectively, and in none of the 67 (0%) and 1 of the 90 (1%) non-acidemic preterms and full-terms, respectively (p<0.001 for preterms, p<0.01 for full-terms). Nine preterms (6 acidemic, 3 non-acidemic) and 2 full-terms (both acidemic) died in the neonatal period. Adverse long-term outcome occurred in 32% of the acidemic preterms, in 21% of the non-acidemic preterms, in 7% of the acidemic full-terms and in 7% of the non-acidemic full-terms.

CONCLUSIONS

Acidemia at birth increased the occurrence of severe IVH in preterm neonates and seizures in both preterm and full-term neonates. However, no significant effect of acidemia on long-term outcome could be demonstrated.

Determining the contribution of asphyxia to brain damage in the neonate

Studies in the research laboratory have demonstrated the complex relationship between fetal and newborn asphyxia and brain damage, a balance between the degree, duration and nature of the asphyxia and the quality of the cardiovascular compensatory response. Clinical studies would support the contention that the human fetus and newborn behave in a similar manner. An accurate diagnosis of asphyxia requires a blood gas and acid base assessment. The clinical classification of fetal asphyxia is based on a measure of metabolic acidosis to confirm that fetal asphyxia has occurred and the expression of neonatal encephalopathy and other organ system complications to express the severity of the asphyxia. The prevalence of fetal asphyxia at delivery is at term, 25 per 1000 live births of whom 15% are moderate or severe; and in the preterm, 73 per 1000 live births of whom 50% are moderate or severe. It remains to be determined how often the asphyxia recognized at delivery may have been present before the onset of labor. There is a growing body of indirect and direct evidence to support the contention that antepartum fetal asphyxia is important in the occurrence of brain damage. Although much of the brain damage observed in the newborn reflects events that occurred before delivery, newborn asphyxia and hypotension, particularly in the preterm newborn, may contribute to the brain damage accounting for deficits in surviving children.

Necrotic cell injury in the preterm and near-term ovine fetal brain after intermittent umbilical cord occlusion

OBJECTIVE

This study was undertaken to determine the extent of necrotic cell death as a measure of neurologic injury in the preterm and near-term ovine fetal brain in response to intermittent umbilical cord occlusion (UCO) with severe, but limited hypoxia and no cumulative acidosis to ensure longer-term survival.

STUDY DESIGN

Fetal sheep (control and experimental groups at 0.75 and 0.90 of gestation) were studied over 4 days with UCOs performed in the experimental group animals by complete inflation of an occluder cuff for 90 seconds every 30 minutes for 3 to 5 hours each day. Animals were then euthanized and the fetal brain perfusion-fixed and prepared for subsequent histology and assessment of necrotic cell injury by using standard staining with hematoxylin and eosin (H&E), and with a novel fluorescent marker, Fluoro-Jade B, that targets degenerating neurons.

RESULTS

In both preterm and near-term animal groups, UCO caused a large decline in arterial Po(2) (to approximately 7 mm Hg), a modest decline in pH (to approximately 7.30), and a modest rise in Pco(2) (to approximately 61 mm Hg) (all P<.01), but with a return to control values after the occluder release and no cumulative acidosis over each day of study. Overall, very low levels of H&E-stained necrotic-appearing cells and Fluoro-Jade B-stained positive cells were observed across all brain regions studied with values not significantly different from zero, excepting that for the gray matter of the preterm control (by H&E staining), preterm and near-term cord occlusion (by H&E and Fluoro-Jade B staining), and the thalamus of the near-term cord occlusion (by H&E staining) animals. Although there were no differences in the levels of H&E-stained necrotic-appearing cells and Fluoro-Jade B-stained positive cells between respective control and cord occlusion group animals for most of the brain regions studied, a significant increase in Fluoro-Jade B-stained positive cells was observed in the gray matter of both the preterm and near-term cord occlusion animals (P<.05).

CONCLUSION

Intermittent cord occlusion insult with severe but limited fetal hypoxemia and no cumulative acidosis, was generally well tolerated in both the preterm and near-term animal groups as assessed by measures of necrotic cell injury throughout the brain with minimal evidence for such. However, compensatory mechanisms which are protective for the brain may become limited with repetitive hypoxia insult over time as suggested by the low level of Fluoro-Jade B-stained positive cells noted in the gray matter tissues for both occlusion groups.

Reflections on the occurrence and significance of antepartum fetal asphyxia

This chapter documents the growing evidence of the occurrence and significance of antepartum fetal asphyxia. Perinatal mortality studies demonstrate that the majority of fetal deaths, including those due to asphyxia, occur in the antepartum period. Epidemiological studies of cerebral palsy conclude that a minority of cases of cerebral palsy are due to intrapartum fetal asphyxia and implicate antenatal events, including asphyxia. Cordocentesis studies have confirmed that antepartum fetal asphyxia occurs in the growth-restricted fetus and might contribute to the increase of stillbirths and cerebral palsy in these children. Blood gas and acid-base studies in the immature fetus have demonstrated the increased prevalence of fetal asphyxia, and particularly of moderate or severe asphyxia, of which the majority might occur in the antepartum period. The ultimate determination of the prevalence and significance of antepartum fetal asphyxia requires the development of a non-invasive specific measure of fetal asphyxia.

The effects of asphyxia on renal function in fetal sheep at midgestation

To determine whether damage to the fetal kidneys plays a role in the formation of hydrops fetalis following a severe asphyxial episode, six chronically catheterised fetal sheep, at 0.6 gestation (90 days; term 150 days), were subjected to 30 min of complete umbilical cord occlusion. During the occlusion period, mean arterial pressure, heart rate and renal blood flow decreased (P < 0.001). There were falls in arterial pH and PO2 and a rise in PCO2 (P < 0.001). Urine flow rate decreased (P < 0.005), as did the excretion rates of sodium and osmoles (P < 0.05). However, by 60 min after release of occlusion, urine flow rate was similar to control values. By the end of day 1, most renal variables returned to normal. At post-mortem, 72 h after occlusion, all asphyxiated fetuses showed gross signs of hydrops. Body weight was higher (P < 0.05) due to fluid accumulation in the peritoneal (P < 0.001) and pleural cavities (P < 0.05) as well as subcutaneously (P < 0.05). Amniotic/allantoic fluid volume was increased (P < 0.05). Kidney histology was normal except for clusters of apoptotic cells in some proximal tubules. In conclusion, this severe asphyxial episode caused surprisingly little damage to the kidney and the changes in renal function were very transient. Thus renal damage was not important in the development of hydrops. Possibly, the midgestation fetal kidney has a limited capacity to increase urinary salt and water excretion in response to increased fluid delivery across the placenta.

Antepartum fetal asphyxia in the preterm pregnancy

OBJECTIVE

The objective of this report was to provide insight into the frequency and characteristics of antepartum fetal asphyxia in pregnancies that are delivered preterm.

STUDY DESIGN

The characteristics of 30 pregnancies that were delivered preterm with biochemically confirmed antepartum fetal asphyxia (umbilical artery base deficit of >12 mmol/L) that were derived from >1 decade of experience in a single tertiary care obstetric unit were examined. Antepartum clinical characteristics, fetal assessment tests, and neonatal complications were documented. Fetal asphyxia was classified as mild, moderate, or severe on the basis of an umbilical artery base deficit (>12 mmol/L) and newborn encephalopathy and other organ system complications.

RESULTS

Antepartum fetal asphyxia accounted for at least 34% of the fetal asphyxia in the pregnancies that were delivered preterm. Predictive criteria that led to intervention and diagnosis included clinical risk factors and, particularly, abnormal fetal assessment tests. The 50% incidence of moderate or severe asphyxia in the antepartum preterm pregnancies compares with 15% in term pregnancies. Moderate or severe asphyxia occurred with equal frequency with early and delayed intervention.

CONCLUSION

Fetal asphyxia in pregnancies that were delivered preterm is present frequently before the onset of labor. Abnormal fetal assessment tests are valuable predictors of antepartum fetal asphyxia. The increased frequency of moderate and severe fetal asphyxia in the pregnancy that is delivered preterm implies a greater likelihood of long-term morbidity or death.

The prediction and prevention of intrapartum fetal asphyxia in preterm pregnancies

OBJECTIVE

This study was undertaken to examine the contribution of electronic fetal heart rate monitoring in the prediction and prevention of intrapartum fetal asphyxia in the preterm pregnancy.

STUDY DESIGN

The outcome of 40 pregnancies with biochemically confirmed intrapartum fetal asphyxia (ie, an umbilical artery base deficit >12 mmol/L) was examined. This included 20 pregnancies that were delivered abdominally matched with 20 pregnancies that were delivered vaginally. Antepartum and intrapartum clinical risk factors and newborn complications were documented. The interpretation of the fetal heart rate record as determined by the responsible clinicians was recorded. Fetal asphyxia was classified as mild, moderate, or severe on the basis of an umbilical artery base deficit of >12 mmol/L and newborn encephalopathy and other organ system complications.

RESULTS

Fetal asphyxia was classified as mild in 21 pregnancies and as moderate or severe in 19 pregnancies. The fetal heart rate record was predictive of fetal asphyxia in 27 pregnancies and nonpredictive in 11 pregnancies. The predictive fetal heart rate record was the primary indication for intervention in 21 of the 24 pregnancies that were delivered by cesarean delivery in the first stage or operative vaginal delivery in the second stage of labor. Newborn outcome may have been influenced by intervention and delivery because of a predictive fetal heart rate record in 10 pregnancies with mild fetal asphyxia and in 9 pregnancies with moderate or severe fetal asphyxia.

CONCLUSION

Electronic fetal monitoring is a useful screening test for the prediction of intrapartum fetal asphyxia in the preterm pregnancy. A predictive fetal heart rate record was the principle indication that led to intervention and delivery. A prediction of fetal asphyxia that leads to intervention and delivery may prevent or modify moderate or severe newborn morbidity as the result of fetal asphyxia.

Correlation of head-to-body delivery intervals in shoulder dystocia and umbilical artery acidosis

OBJECTIVE

Our goal was to determine the effect of shoulder dystocia on umbilical artery acidosis.

STUDY DESIGN

We performed a retrospective analysis of 134 mother-infant pairs of shoulder dystocia cases at our institution from January 1, 1994, through December 31, 1997. Cases were identified from the obstetric database, and charts were abstracted for demographics, head-to-body delivery interval, umbilical blood gas parameters, and neonatal outcome. Pooled student t tests were used to compare mean blood gas values with data previously reported from our patient population. Regression analysis was performed regarding head-to-body delivery interval and blood gas parameters.

RESULTS

The mean umbilical artery pH of shoulder dystocia cases (7.23 +/-.082) was less than the mean arterial pH of all vaginal deliveries in our institution (7.27 +/-.069), P <.001. Head-to-body delivery intervals (available for 44 cases) were not associated with statistically significant alterations in umbilical artery pH (r(2) =.0004), PCO(2) (r(2) =.011), or base deficit (r(2) =.006). Increasing head-to-body delivery interval was also not significantly correlated with decreasing 5-minute Apgar score (r =.0278).

CONCLUSION

In our study population, shoulder dystocia resulted in statistically significant but clinically insignificant reductions in mean umbilical artery blood gas parameters. No statistically significant linear relationship was identified between the head-to-body delivery interval and fetal acid-base status.

Hypoxic-ischemic brain injury in the newborn: pathophysiology and potential strategies for intervention

There is increasing clinical and experimental data describing the evolution of hypoxic-ischemic encephalopathy in the perinatal period. Outcome to the fetus is determined not only by the impact of gross asphyxial insult, but also external factors that sensitize the brain to injury. Delayed neuronal and glial death occurring in the hours and days after the insult by apoptotic and related processes are observed following severe injury, and offer the most promise for pharmacological intervention. Furthermore, new technologies allow the identification of subtle insults with evolving encephalopathies that have implications for long-term neurological outcome. Application of this knowledge will allow us to identify strategies for early intervention and prevent the course of damage caused by hypoxic-ischemic injury.

Transient intrauterine hypotension: effect on newborn rat brain

Intrauterine perfusion failure can cause cerebral malformations. We investigated the effect of transient maternal hypotension on newborn rat brain by inducing hypovolemic hypotension for 2.5 h during early embryonic day 7 (E7) or late (E15) gestation in pregnant rats. We found an increase in the number of TUNEL-positive cells within the periventricular germinative matrix in pups subjected to early gestational hypotension and within the cerebral cortex in those subjected to late gestational hypotension in comparison to sham control animals. These results suggest that episodic maternal hypovolemic hypotension may affect the fetal brain, and apoptotic mechanisms may mediate this effect.

Circulatory effects of acute bradycardia in the human fetus as studied by Doppler ultrasound

OBJECTIVE

To report on flow changes in fetal arterial, venous and coronary vessels during bradycardia following cordocentesis. Changes in the fetal circulation in response to acute challenges are incompletely understood.

METHODS

Fetal blood sampling was performed at 29 + 4 weeks for chromosome analysis in a fetus with multiple malformations including a complete atrioventricular septal defect with competent atrioventricular valve. The procedure was complicated by a 12-min bradycardia of 57 beats/min. 'Heart sparing' (sudden visualization of coronary blood flow) and 'brain sparing' (increased diastolic velocities in the middle cerebral artery) were demonstrated by Doppler examination despite marked circulatory compromise (regurgitation of atrioventricular valve, increased reverse flow in precordial veins and pulsatile umbilical vein flow pattern) which persisted after normalization of the fetal heart rate. The findings had resolved completely at a full cardiovascular examination 6 h after the bradycardia. Pregnancy termination was subsequently performed for partial monosomy 13q.

CONCLUSION

Protective fetal changes producing 'heart sparing' and 'brain sparing' and may be operational during episodes of acute fetal bradycardia.

The PR interval-fetal heart rate relationship during repetitive umbilical cord occlusions in immature fetal sheep

OBJECTIVE

To evaluate the relationship of the PR interval and fetal heart rate during repetitive umbilical cord occlusions in immature sheep fetuses.

STUDY DESIGN

In seven chronically cannulated immature sheep fetuses [gestational age 90.6 days (mean)], we analyzed continuous fetal electrocardiogram recordings during repetitive cord occlusions for 2 out of every 5 min until fetal mean arterial pressure dropped to 50% of baseline value. PR interval-fetal heart rate correlation coefficients (Pearson) was measured on consecutive blocks of 2.5 min. R-values of the baseline and the repetitive occlusion period were compared by Fisher's exact test.

RESULTS

Repetitive cord occlusions resulted in acidosis and hypotension. Two fetuses died at the end of the repetitive occlusion period. Four out of seven fetuses showed a significant change from a negative relationship between the PR interval and fetal heart rate during baseline to a predominantly positive relationship during the repetitive occlusion period.

CONCLUSION

In immature fetal sheep, a change from a negative relationship between the PR interval and fetal heart rate to a predominantly positive relationship between the PR interval and fetal heart rate was observed in four out of seven fetuses following the initiation of repetitive umbilical cord occlusions.

Fetal arterial pressure and heart rate changes in surviving and non-surviving immature fetal sheep following brief repeated total umbilical cord occlusions

OBJECTIVES

To describe the changes in fetal heart rate and mean arterial pressure during repetitive total umbilical cord occlusions in immature sheep fetuses, resulting in severe asphyxia or fetal death. To describe the relationship between these changes and concurrent changes in acid-base status.

STUDY DESIGN

We performed brief repeated total umbilical cord occlusions, two out of every five min, in 14 immature sheep fetuses (at 90 days of gestation), until fetal mean arterial pressure dropped below 50% of baseline value during two successive occlusions. Fetal blood gas analyses were performed at regular intervals just before cord occlusions.

RESULTS

Progressive acidemia and hypotension developed with ongoing occlusions. The degree of hypotension during occlusions increased with ongoing occlusions. The minimum fetal arterial blood pressure during occlusions correlated well with the progressive acidemia. Six fetuses died at the end of the repetitive occlusion period. In the non-survivors, acidemia was more severe and paCO2 gradually increased during the entire repetitive occlusion period. In the survivors group, a period of transient hypoxia and hypotension was observed with a nadir at +60 min following the final occlusion.

CONCLUSION

Repetitive umbilical cord occlusions in immature sheep fetuses resulted in repetitive periods of hypotension, bradycardia, progressive fetal acidemia and ultimately fetal demise. Minimum fetal arterial blood pressure during occlusions correlated well with the progressive fetal acidemia.

The cardiovascular and cerebrovascular responses of the immature fetal sheep to acute umbilical cord occlusion

1. In premature fetal sheep (89-93 days gestation) we examined the fetal response to asphyxia induced by 30 min of complete umbilical cord occlusion. Fetuses were also studied during the first 3 days after asphyxia. We measured heart rate, blood pressure, carotid and femoral blood flows, vascular resistance, electroencephalographic activity and cerebral changes in haemoglobin concentration by near infrared spectroscopy (NIRS). 2. Fetuses tolerated 30 min of asphyxia and the cardiovascular response was characterized by three phases: initial redistribution of blood flow away from the periphery to maintain vital organ function, partial failure of this redistribution and near terminal cardiovascular collapse, with profound hypotension and cerebral and peripheral hypoperfusion. 3. Post-asphyxia carotid blood flow and NIRS data demonstrated that between 3-5 h there was a significant secondary reduction in cerebral blood flow, blood volume and oxygenation despite normal perfusion pressure and heart rate. There was also a secondary fall in femoral blood flow which persisted throughout recovery. 4. These data demonstrate that the immature fetus can survive a prolonged period of asphyxia, but paradoxically the capacity to survive exposes the fetus to profound hypotension and hypoperfusion. A secondary period of significant cerebral hypoperfusion and reduced oxygen delivery also occurred post-asphyxia. These cardiovascular and cerebrovascular responses may contribute to the patterns of cerebral injury seen in the human preterm fetus.