Polymicrogyria in a fetus with human parvovirus B19 infection: a case with radiologic-pathologic correlation.

We report the prenatal magnetic resonance imaging (MRI) appearance of polymicrogyria with pathologic correlation in a fetus with congenital parvovirus B19 infection. Prenatal ultrasound revealed non-immune hydrops, but detected no fetal brain abnormalities. A subsequent fetal MRI scan performed at 23 weeks' gestation demonstrated bilateral polymicrogyria, which was confirmed at autopsy. To our knowledge, prenatal diagnosis of polymicrogyria in association with congenital parvovirus B19 infection has not been previously described. This case provides further evidence for brain abnormalities resulting from congenital parvovirus B19 infection, and suggests that fetal neuroimaging with MRI would be of value in suspected cases of congenital parvovirus infection.

Fetal and postnatal pulmonary circulation in the Alto Andino.

Lowland mammals at high altitude constrict the pulmonary vessels, augmenting vascular resistance and developing pulmonary arterial hypertension. In contrast, highland mammals, like the llama, do not present pulmonary arterial hypertension. Using wire myography, we studied the sensitivity to norepinephrine (NE) and NO of small pulmonary arteries of fetal llamas and sheep at high altitudes. The sensitivity of the contractile responses to NE was decreased whereas the relaxation sensitivity to NO was augmented in the llama fetus compared to the sheep fetus. Altogether these data show that the fetal llama has a lower sensitivity to a vasoconstrictor (NE) and a higher sensitivity to a vasodilator (NO), than the fetal sheep, consistent with a lower pulmonary arterial pressure found in the neonatal llama in the Andean altiplano. Additionally, we investigated carbon monoxide (CO) in the pulmonary circulation in lowland and highland newborn sheep and llamas. Pulmonary arterial pressure was augmented in neonatal sheep but not in llamas. These sheep had reduced soluble guanylate cyclase and heme oxygenase expression and CO production than at lowland. In contrast, neonatal llamas increased markedly pulmonary CO production and HO expression at high altitude. Thus, enhanced pulmonary CO protects against pulmonary hypertension in the highland neonate. Further, we compared pulmonary vascular responses to acute hypoxia in the adult llama versus the adult sheep. The rise in pulmonary arterial pressure was more marked in the sheep than in the llama. The llama pulmonary dilator strategy may provide insights into new treatments for pulmonary arterial hypertension of the neonate and adult.

Fetal acidemia and electronic fetal heart rate patterns: is there evidence of an association?

OBJECTIVE: Despite the ubiquity of electronic fetal monitoring, the validity of the relationship between various fetal heart rate (FHR) patterns and fetal acidemia has not yet been established in a large unselected series of consecutive pregnancies. The aim of this study was to examine the published literature for evidence of such a relationship. METHODS: Four hypotheses based on assumptions in common clinical use were examined. The literature was searched for relationships between certain aspects of FHR patterns (e.g., degree of FHR variability, depth of decelerations), and fetal acidemia, or fetal vigor (5-minute Apgar score >or=7). We also attempted to relate duration of these patterns to the degree of acidemia. Using standardized FHR nomenclature we defined patterns based on baseline FHR variability, baseline rate, decelerations, and accelerations. RESULTS: The following relationships were observed: (1) Moderate FHR variability was strongly associated (98%) with an umbilical pH >7.15 or newborn vigor (5-minute Apgar score >or=7). (2) Undetectable or minimal FHR variability in the presence of late or variable decelerations was the most consistent predictor of newborn acidemia, though the association was only 23%. (3) There was a positive relationship between the degree of acidemia and the depth of decelerations or bradycardia. (4) Except for sudden profound bradycardia, newborn acidemia with decreasing FHR variability in combination with decelerations develops over a period of time approximating one hour. Most studies identified were observational and uncontrolled (grade III evidence of US Preventive Services Task Force); however, there was general agreement amongst the various studies, strengthening the validity of the observations. CONCLUSIONS: The validity of the relationship between certain FHR patterns and fetal acidemia and/or vigor, is supported by observations from the literature. In addition four assumptions commonly used in clinical management are supported. These conclusions need to be confirmed by a prospective examination of a large number of consecutive, unselected FHR patterns, and their relationship to newborn acidemia. Pending the completion of such studies, these observations can be used to justify certain aspects of current clinical management, and may assist in standardizing the diversity of opinions regarding FHR pattern management.

Tocolysis with beta-adrenergic receptor agonists.

Beta-adrenergic receptor agonists have been used for tocolysis in the setting of preterm labor for more than three decades. One of these agents, ritodrine hydrochloride, is the only Federal Drug Administration (FDA) approved drug for the treatment of preterm labor. Despite their widespread use, only a few prospective randomized placebo-controlled trials have been performed. These agents have been shown to have more patients deliver beyond 48 hours after the onset of treatment as compared with controls, but have never shown a difference in neonatal outcomes. Because they are one of the few tocolytic agents to have been shown to make a difference when compared with controls, the beta-agonists are commonly used as the control groups in studies examining the efficacy of newer tocolytic agents. In general, agents such as nifedipine, magnesium sulfate, and atosiban have not been shown to be more efficacious than the beta-agonists. However, several studies have shown these agents to have less side effects and lower discontinuation rates than the beta-agonists.

Fructose- 1,6-bisphosphate did not affect hippocampal neuronal damage caused by 10 min of complete umbilical cord occlusion in fetal sheep.

Fructose-1, 6-bisphosphate (FBP) has a neuroprotective effect in neonatal and adult rats. The purpose of this study was to examine the effects of FBP on hippocampal neuronal damage in fetal sheep asphyxiated by 10 min of complete umbilical cord occlusion. Thirteen fetal sheep at 124 days of gestation were surgically instrumented with catheters. Cardiorespiratory parameters were monitored, and biochemical analyses were performed with the blood samples. During the insult seven fetuses were given FBP (500 mg/kg) and six were given iso-osmotic saline, and hippocampal neuronal damage was examined histologically and scored. Cardiorespiratory changes were the same in both groups, and there was no neuroprotective effect of FBP in this study. However the decrease of serum total Ca level implied the Ca- chelating effect of FBP.

Fetal heart rate monitoring: is it salvageable?

Fetal heart rate monitoring was introduced in the 1960s. After a number of randomized controlled trials in the mid 1980s, doubt arose regarding the efficacy of fetal heart rate monitoring in improving fetal outcome. The potential reasons why fetal heart rate monitoring has not been shown to be efficacious are (1) use of an outcome measure that is not related to variant fetal heart rate monitoring patterns, (2) lack of standardized interpretation of fetal heart rate patterns, (3) disagreement regarding algorithms for intervention of specific fetal heart rate patterns, and (4) the inability to demonstrate the reliability, validity, and ability of fetal heart rate monitoring to allow timely intervention. A recent National Institutes of Health committee proposed detailed, quantitative, standardized definitions of fetal heart rate patterns, which can serve as a basis for determining whether fetal heart rate monitoring is reliable and valid. In this article we examine reasons why fetal heart rate monitoring did not live up to its original expectations and why the randomized controlled trials did not demonstrate efficacy, and we make suggestions for determining whether electronic fetal heart rate monitoring should be abandoned.

Histologic and biochemical study of the brain, heart, kidney, and liver in asphyxia caused by occlusion of the umbilical cord in near-term fetal lambs.

OBJECTIVE: We sought to determine the relationship between the degree of histologic changes in the brain, heart, kidney, and liver in fetal lambs after severe asphyxia and to analyze the role of oxidative stress in the pathogenesis of fetal multiple organ failure. STUDY DESIGN: Eight chronically instrumented near-term fetal lambs were asphyxiated by partial umbilical cord occlusion for approximately 60 minutes until the fetal arterial pH reached <6.9 and the base excess reached <-20 mEq/L. An additional 6 fetuses were used as sham-asphyxiated controls. Fetal heart rates, blood pressure, fetal breathing movements, and arterial blood gases and acid-base states were serially monitored. The brain, heart, kidney, and liver were collected 72 hours after asphyxia, processed, and histologically examined after hematoxylin and eosin staining. Fetal brain histologic features were classified into 5 grades, with 5 being the most severe damage. The other organs were examined histologically by pathologists who were blinded to the treatment. Each organ was assayed for tissue concentrations of thiobarbituric acid-reactive substances, superoxide dismutase, glutathione, lactate, and glucose. RESULTS: Myocardial changes of necrosis, phagocytosis, and contraction bands occurred in only 2 of the most severely (grade 5) brain-damaged fetuses. The same 2 cases showed fatty changes and congestion in the liver. In the kidney all asphyxiated cases showed tubular necrosis, but glomeruli were generally spared. Of the measures of oxidative stress, only liver tissue levels of thiobarbituric acid-reactive substances and superoxide dismutase were significantly higher in the asphyxiated group than in the control group, but there was no correlation with the degree of damage. Lactate level was higher only in the heart in the asphyxiated fetuses. CONCLUSION: Renal tubular damage was seen with all degrees of asphyxia, despite variable brain damage. Histologic changes in the myocardium and liver were seen only with the most severe brain damage. Oxidative stress appears to play a role in the pathogenesis of liver damage.

Fetal heart rate monitoring: interpretation and collaborative management.

Effective intrapartum fetal heart rate (FHR) monitoring requires ongoing collaboration among health care providers. Nurses, midwives, and physicians must have a shared understanding of 1) how FHR tracings are interpreted, 2) which FHR patterns are associated with actual or impending fetal acidemia, 3) when and within what time frame the physician or the midwife should be notified of variant FHR patterns, 4) how quickly physicians and midwives should respond when notified of variant patterns, and 5) the indications for and optimal timing of interventions such as operative delivery. This article reviews the literature on FHR monitoring and includes a discussion of the advantages and limitations of different monitoring modalities. An overview of those FHR patterns are associated with presumed fetal acidemia is presented, as well as sample multidisciplinary FHR monitoring guidelines and an exercise in intrapartum FHR pattern evaluation that can be used to initiate development of local FHR monitoring patterns.

Cardiovascular responses to arginine vasopressin blockade during acute hypoxemia in the llama fetus.

The fetal llama has a marked increase in the peripheral vascular resistance and no augmentation of brain blood flow during hypoxemia. In spite of the substantial plasma arginine-vasopressin (AVP) increase during hypoxemia, up to 8 times greater than in fetal sheep, there are no changes of carotid and femoral blood flows during hypoxemia with a V1 receptor blockade, as is seen in the fetal sheep. The aim of this study was to assess the role of AVP function in mediating the combined ventricular output and organ blood flow in the hypoxemic llama fetus. Six fetal llamas at 0.65 of gestation were instrumented under general anesthesia, and cardiorespiratory responses and blood flows determined under normoxemic and hypoxemic conditions. The AVP effect was determined using a V1 antagonist during normoxemic and hypoxemic conditions. Organ blood flows were measured with the radioactive microsphere technique. No significant differences in organ blood flow or in their vascular resistances were seen between the control and treated fetuses during hypoxemia. We conclude that V1 blockade did not have any important role in the cardiovascular response to acute hypoxemia in the llama fetus, in contrast with lowland fetuses. AVP may be playing a role in other regions, possibly in kidney or lung, during hypoxemia.

The physiology of fetal heart rate patterns and perinatal asphyxia.

The purpose of electronic fetal heart rate (FHR) monitoring is the ongoing assessment of fetal oxygenation. FHR tracings are analyzed for characteristic patterns that signify specific hypoxic or nonhypoxic events. A working knowledge of fetal physiology and the fetal response to hypoxia can aid and refine clinical interpretation of FHR patterns during labor. This article reviews the fetal response to decreased oxygenation, the physiology of subsequent FHR patterns and the clinical presentation of asphyxia in the newborn.

Obstetric evaluation of fetal acid-base balance.

Several techniques may be used to evaluate fetal acid-base status during the ante- and intrapartum periods. Percutaneous blood sampling (cordocentesis) may be used to measure standard blood-gas parameters while the fetus is still in utero, but because of the risks associated with such procedures and the limited clinical utility of the results, this procedure is recommended for blood gas analysis only as part of a research protocol. Intrapartum blood specimens may be safely obtained via fetal scalp sampling, but the need for such sampling has been dramatically reduced by the use of other noninvasive tests such as fetal scalp stimulation or vibroacoustic stimulation. Finally, assay of blood obtained from a segment of umbilical cord collected at delivery indicates acid-base status at birth, but the range of normal values is wide, and only the most abnormal results have any prognostic significance.

Multiple courses of antenatal corticosteroids and outcome of premature neonates. North American Thyrotropin-Releasing Hormone Study Group.

OBJECTIVES: We sought to examine outcome for premature neonates after multiple courses of antenatal corticosteroids compared with a single course. STUDY DESIGN: We performed a post hoc nonrandomized analysis on 710 neonates of 25-32 weeks' gestation who were born to mothers enrolled in the North American Thyrotropin-Releasing Hormone Trial and who received 1, 2, or >/=3 courses of antenatal corticosteroids. RESULTS: There was no detectable clinical difference in incidence of respiratory distress syndrome, chronic lung disease, and intraventricular hemorrhage related to courses of antenatal corticosteroids, and outcome was similar for infants delivered at 7-13 days compared with those delivered at 1-6 days after receiving antenatal corticosteroids. Compared with those who received a single course, neonates who received >/=2 courses had lower birth weights (-39 g, P =.02), and those receiving >/=3 courses had increased risk of death (adjusted odds ratio, 2.8; 95% confidence interval, 1.3-5.9; P =.01) and lower levels of plasma cortisol at age 2 hours. CONCLUSION: In this retrospective analysis multiple courses of antenatal corticosteroids did not improve outcome and were associated with increased mortality, decreased fetal growth, and prolonged adrenal suppression.

Fetal heart rate patterns in postasphyxiated fetal lambs with brain damage.

OBJECTIVE: We previously showed that in asphyxiated fetal lambs the duration of hypotension correlated well with the severity of histologic damage to the brain, whereas the duration of bradycardia did not. This study compares fetal heart rate patterns with the degree of histologic damage to the brain. STUDY DESIGN: Twelve chronically instrumented near-term fetal lambs were subjected to asphyxia by umbilical cord occlusion until fetal arterial pH was <6. 9 and base excess was <-20 mEq/L. An additional 4 fetuses served as sham-asphyxia controls. Fetal heart rate (from electrocardiogram), arterial blood pressure, fetal breathing movements, and electrocorticogram were continuously monitored before, during, and for 72 hours after asphyxia. Fetal brain histologic features were categorized as mild (group 1, n = 5), moderate (group 2, n = 4), and severe (group 3, n = 3). Long-term fetal heart rate variability expressed as amplitude range was assessed visually every 5 minutes from 30 minutes before asphyxia until 2 hours of recovery and at 6, 12, 24, 48, and 72 hours of recovery. RESULTS: Long-term fetal heart rate variability amplitude decreased from 32 +/- 17 beats/min (mean +/- SEM) preocclusion to 4 +/- 13 beats/min at the end of occlusion (P <.001) without significant differences among the 3 groups. During 10 to 45 minutes of recovery, the long-term variability of group 1 was significantly greater than that of groups 2 and 3. At 24 to 72 hours of recovery, the long-term variability of groups 1 and 2 was significantly higher than that of group 3, which was almost 0. The "checkmark" and sinusoidal fetal heart rate patterns were observed during the recovery period in groups 2 and 3. CONCLUSIONS: Decreased long-term fetal heart rate variability and the "checkmark" and sinusoidal fetal heart rate patterns were indicators of the severity of asphyxial histologic damage in the fetal brain.

Cardiorespiratory responses to acute hypoxemia in the chronically catheterized fetal llama at 0.7-0.9 of gestation.

The adult llama (Lama glama) has several compensatory mechanisms that allow it to successfully survive at high altitude. Llama fetuses at 0.6-0.7 of gestation, and near-term llama fetuses studied close to surgery, did not increase cerebral blood flow and decreased cerebral oxygen delivery during acute hypoxemia. It is not known whether these responses were the result of immaturity or surgical stress. The aim of this study was to determine whether the lack of increase in cerebral blood flow and the decrease in cerebral oxygen delivery during hypoxemia in the fetal llama is characteristic of this high-altitude species near term, and under nonstressed conditions. We chronically catheterized 7 llamas and their fetuses near to term, at 0.7-0.9 of gestation. Fetal cardiac output, cerebral and regional blood flows, systemic blood pressure, heart rate, pH, and blood gases, organ vascular resistances and organ oxygen deliveries were determined at least 4 days after surgery, both during the basal state and after 1 hr of acute fetal hypoxemia. During hypoxemia the llama fetus did not increase cerebral blood flow and markedly decreased its cerebral oxygen delivery. There was also a marked decrease in kidney blood flow and oxygen delivery. These results indicate that, in contrast to fetuses of lowland species, the fetal llama does not increase the cerebral blood flow during hypoxemia, suggesting specific cellular mechanisms to preserve brain integrity during oxygen limitation.

Effects of fetal asphyxia on brain cell structure and function: limits of tolerance.

The objective of this paper is to review the published information available on the effect of hypoxia on fetal cerebral integrity, and to attempt to define limits of fetal tolerance to asphyxia Data were obtained in experimental animals following imposed hypoxia or asphyxia. Studies were carried out in the fetus by physiologic, biochemical, histologic, and behavioral techniques. Human data were collected from newborns at birth and during subsequent development. It has been established that acute asphyxia of the fetus in utero may result in a spectrum of effects on the fetus, including death, or survival with permanent neurologic damage, or apparent complete recovery. The severity of damage depends on the degree and duration of asphyxia and a number of sensitizing factors, including prior metabolic and cardiovascular status of the fetus, differential sensitivity of the heart and brain to asphyxia, gestational age, plasticity, intermittency of asphyxial insults, and the pattern of intermittency. The fetus has a number of compensatory mechanisms that allow it to survive periods of oxygen limitation without permanent damage to the brain. The fetus can increase cerebral blood flow to increase oxygen delivery to the brain, and can decrease its metabolism by electrophysiological and behavioral state changes. Cerebral ischemia and reduced metabolism to < 50% of control is probably necessary for permanent brain damage to occur. In human pregnancy, factors consistent with intrapartum asphyxia lasting until delivery as a cause of fetal neurologic damage include absent fetal heart rate variability, umbilical cord arterial pH < 6.8, base access < -20 mEql-1, severe and prolonged newborn depression with Apgar score of < or = 3 at 10 min, seizure activity in the first day of life, and damage to the noncerebral organs and regions. However, these factors are neither independently nor collectively predictive of asphyxial brain damage. It is concluded that permanent neurologic damage or death can occur in the fetus due to single or repetitive episodes of hypoxia or asphyxia, but it is not yet possible to predict the occurrence or extent of such damage in an individual fetus.

Brain lipid peroxidation and antioxidant levels in fetal lambs 72 hours after asphyxia by partial umbilical cord occlusion.

OBJECTIVES: The purpose of this study was to explain the role of oxidative stress in the pathogenesis of brain damage caused by intrauterine fetal asphyxia. STUDY DESIGN: Six chronically instrumented near-term fetal lambs were subjected to asphyxia by partial umbilical cord occlusion for approximately 60 minutes until fetal arterial pH diminished to less than 6.9 and base excess to less than -20 mEq. Another six fetuses surgically prepared but not occluded were used as control. Fetuses were killed after 72 hours and eight different brain regions (frontal and parietal gray matter, frontal and parietal white matter, basal ganglia, thalamus, hippocampus, and cerebellum) were dissected and assayed for thiobarbituric acid reactive substances, glutathione, and superoxide dismutase. RESULTS: Thiobarbituric acid reactive substance levels in asphyxiated animals were elevated in frontal and parietal white matter, basal ganglia, and thalamus compared with those in controls. The concentrations of superoxide dismutase in the asphyxiated group were also higher in frontal and parietal white matter, basal ganglia, and cerebellum compared with those in the control group. Between the two groups, however, glutathione concentrations did not differ significantly. CONCLUSION: These results suggest that oxidative stress may be a major contributing factor to the development of brain damage in intrauterine fetal asphyxia.

Physiologic and histologic changes in near-term fetal lambs exposed to asphyxia by partial umbilical cord occlusion.

OBJECTIVES: Our purpose was to characterize the histologic changes in the asphyxiated fetal lamb brain and to correlate the severity of these changes with fetal physiologic parameters during and after asphyxia. STUDY DESIGN: Seventeen near-term fetuses were used for analysis: control group without manipulation (n = 4, 132 +/- 1.1 days of gestation at autopsy, mean +/- SEM), sham-asphyxia control group (n = 3, 132 +/- 1.3 days), and asphyxiated group, which successfully survived 72 hours after asphyxia (n = 10, 130 +/- 1.0 days). Asphyxia was produced by umbilical cord occlusion lasting for approximately 60 minutes until fetal arterial pH diminished to < 6.9 and base excess to < -20 mEq/L. Fetal heart rate, blood pressure, and electrocorticographic activity were continuously monitored. The fetuses were killed 72 hours after asphyxia, and the brains were fixed in formalin and processed for histologic and immunocytochemical studies. RESULTS: Neuropathologic changes varied from case to case, ranging from almost total infarction of cortical and subcortical structures to extremely subtle and patchy white matter alterations characterized by slight vacuolization of the white matter or slight to moderate increases in cellularity confined to the junction of cerebral cortex and white matter. Even fetuses that showed full recovery of all physiologic parameters, including electrocorticographic activity, demonstrated subtle but distinct white matter lesions. The gray matter, including the hippocampal neurons, was generally spared in these cases. Electrocorticographic parameters, duration of hypotension during asphyxia, and delayed recovery of blood lactate concentrations correlated well with the histologic grading of brain damage. CONCLUSIONS: Asphyxia by partial umbilical cord occlusion in near-term fetal lambs produces variable neuropathologic changes. The mildest change is a white matter lesion characterized by vacuolization and loss of myelin or by increased cellularity in the damaged regions.