Antenatal Magnesium Sulfate Benefits Female Preterm Infants but Results in Poor Male Outcomes.

Magnesium sulfate (MagSul) is used clinically to prevent eclamptic seizures during pregnancy and as a tocolytic for preterm labor. More recently, it has been implicated as offering neural protection in utero for at-risk infants. However, evidence is mixed. Some studies found that MagSul reduced the incidence of cerebral palsy (CP) but did not improve other measures of neurologic function. Others did not find any improvement in outcomes. Inconsistencies in the literature may reflect the fact that sex effects are largely ignored, despite evidence that MagSul shows sex effects in animal models of neonatal brain injury. The current study used retrospective infant data to assess differences in developmental outcomes as a function of sex and MagSul treatment. We found that on 18-month neurodevelopmental cognitive and language measures, preterm males treated with MagSul (n = 209) had significantly worse scores than their untreated counterparts (n = 135; p < 0.05). Female preterm infants treated with MagSul (n = 220), on the other hand, showed a cognitive benefit relative to untreated females (n = 123; p < 0.05). No significant effects of MagSul were seen among females on language (p > 0.05). These results have tremendous implications for risk-benefit considerations in the ongoing use of MagSul and may explain why benefits have been hard to identify in clinical trials when sex is not considered.

Sex Differences in Microglia Activation in a Rodent Model of Preterm Hypoxic Ischemic Injury with Caffeine Treatment.

Preterm infants are often treated with caffeine as a respiratory stimulant. However, follow-up data shows caffeine may also have neuroprotective potential. There are several theories as to how caffeine might protect the brain, but none have been proven. This study looked at caffeine effects on microglial activation in rodent brains post hypoxic ischemic (HI) injury. Rat pups underwent either sham or HI surgery on P6, followed by treatment with either caffeine or saline. Forty-eight hours post-injury, brains were collected and underwent paraffin embedding and sectioning followed by immunofluorescence staining. Ionized calcium binding adaptor molecule 1 (Iba-1) was used to label microglia, and 4',6-diamindino-2-phenylindole (DAPI) was used to label DNA. Cell size measurements of microglia were obtained to gauge microglia activation, and chromatin condensation (DAPI optical density) was used as an index of neuronal cell death. Results suggest that caffeine does offer protective effects, based on significantly increased levels of cell death in HI-saline animals not seen in caffeine-treated HI males and females. However, the mechanism of action may be different. Male HI animals showed marginally reduced microglial activation following caffeine treatment, whereas females did not. Results indicate that though caffeine may act protectively in both sexes by reducing cell death, the benefits may be mediated by different mechanisms.

Sex Differences in Brain Injury and Repair in Newborn Infants: Clinical Evidence and Biological Mechanisms.

Differences in the development of the male and female brain are an evolving area of investigation. We are beginning to understand the underpinnings of male and female advantages due to differences in brain development as well as the consequences following hypoxic-ischemic brain injury in the newborn. The two main factors that appear to affect outcomes are gestation age at the time of injury and sex of the subject. This review starts with a summary of differences in the anatomy and physiology of the developing male and female brain. This is followed by a review of the major factors responsible for the observed differences in the face of normal development and hypoxic injury. The last section reviews the response of male and female subjects to various neuroprotective strategies that are currently being used and where there is a need for additional information for more precise therapy based on the sex of the infant.

Effects of Sex and Mild Intrainsult Hypothermia on Neuropathology and Neural Reorganization following Neonatal Hypoxic Ischemic Brain Injury in Rats.

Hypoxia ischemia (HI) is a recognized risk factor among late-preterm infants, with HI events leading to varied neuropathology and cognitive/behavioral deficits. Studies suggest a sex difference in the incidence of HI and in the severity of subsequent behavioral deficits (with better outcomes in females). Mechanisms of a female advantage remain unknown but could involve sex-specific patterns of compensation to injury. Neuroprotective hypothermia is also used to ameliorate HI damage and attenuate behavioral deficits. Though currently prescribed only for HI in term infants, cooling has potential intrainsult applications to high-risk late-preterm infants as well. To address this important clinical issue, we conducted a study using male and female rats with a postnatal (P) day 7 HI injury induced under normothermic and hypothermic conditions. The current study reports patterns of neuropathology evident in postmortem tissue. Results showed a potent benefit of intrainsult hypothermia that was comparable for both sexes. Findings also show surprisingly different patterns of compensation in the contralateral hemisphere, with increases in hippocampal thickness in HI females contrasting reduced thickness in HI males. Findings provide a framework for future research to compare and contrast mechanisms of neuroprotection and postinjury plasticity in both sexes following a late-preterm HI insult.

Sex differences in behavioral outcomes following temperature modulation during induced neonatal hypoxic ischemic injury in rats.

Neonatal hypoxia ischemia (HI; reduced oxygen and/or blood flow to the brain) can cause various degrees of tissue damage, as well as subsequent cognitive/behavioral deficits such as motor, learning/memory, and auditory impairments. These outcomes frequently result from cardiovascular and/or respiratory events observed in premature infants. Data suggests that there is a sex difference in HI outcome, with males being more adversely affected relative to comparably injured females. Brain/body temperature may play a role in modulating the severity of an HI insult, with hypothermia during an insult yielding more favorable anatomical and behavioral outcomes. The current study utilized a postnatal day (P) 7 rodent model of HI injury to assess the effect of temperature modulation during injury in each sex. We hypothesized that female P7 rats would benefit more from lowered body temperatures as compared to male P7 rats. We assessed all subjects on rota-rod, auditory discrimination, and spatial/non-spatial maze tasks. Our results revealed a significant benefit of temperature reduction in HI females as measured by most of the employed behavioral tasks. However, HI males benefitted from temperature reduction as measured on auditory and non-spatial tasks. Our data suggest that temperature reduction protects both sexes from the deleterious effects of HI injury, but task and sex specific patterns of relative efficacy are seen.

Dissociation in the Effects of Induced Neonatal Hypoxia-Ischemia on Rapid Auditory Processing and Spatial Working Memory in Male Rats.

Infants born prematurely are at risk for cardiovascular events causing hypoxia-ischemia (HI; reduced blood and oxygen to the brain). HI in turn can cause neuropathology, though patterns of damage are sometimes diffuse and often highly variable (with clinical heterogeneity further magnified by rapid development). As a result, though HI injury is associated with long-term behavioral and cognitive impairments in general, pathology indices for specific infants can provide only limited insight into individual prognosis. The current paper addresses this important clinical issue using a rat model that simulates unilateral HI in a late preterm infant coupled with long-term behavioral evaluation in two processing domains - auditory discrimination and spatial learning/memory. We examined the following: (1) whether deficits on one task would predict deficits on the other (suggesting that subjects with more severe injury perform worse across all cognitive domains) or (2) whether domain-specific outcomes among HI-injured subjects would be uncorrelated (suggesting differential damage to orthogonal neural systems). All animals (sham and HI) received initial auditory testing and were assigned to additional auditory testing (group A) or spatial maze testing (group B). This allowed within-task (group A) and between-task (group B) correlation. Anatomic measures of cortical, hippocampal and ventricular volume (indexing HI damage) were also obtained and correlated against behavioral measures. Results showed that auditory discrimination in the juvenile period was not correlated with spatial working memory in adulthood (group B) in either sham or HI rats. Conversely, early auditory processing performance for group A HI animals significantly predicted auditory deficits in adulthood (p = 0.05; no correlation in shams). Anatomic data also revealed significant relationships between the volumes of different brain areas within both HI and shams, but anatomic measures did not correlate with any behavioral measure in the HI group (though we saw a hippocampal/spatial correlation in shams, in the expected direction). Overall, current data provide an impetus to enhance tools for characterizing individual HI-related pathology in neonates, which could provide more accurate individual prognoses within specific cognitive/behavioral domains and thus improved patient-specific early interventions.

Spatial working memory deficits in male rats following neonatal hypoxic ischemic brain injury can be attenuated by task modifications.

Hypoxia-ischemia (HI; reduction in blood/oxygen supply) is common in infants with serious birth complications, such as prolonged labor and cord prolapse, as well as in infants born prematurely (<37 weeks gestational age; GA). Most often, HI can lead to brain injury in the form of cortical and subcortical damage, as well as later cognitive/behavioral deficits. A common domain of impairment is working memory, which can be associated with heightened incidence of developmental disorders. To further characterize these clinical issues, the current investigation describes data from a rodent model of HI induced on postnatal (P)7, an age comparable to a term (GA 36-38) human. Specifically, we sought to assess working memory using an eight-arm radial water maze paradigm. Study 1 used a modified version of the paradigm, which requires a step-wise change in spatial memory via progressively more difficult tasks, as well as multiple daily trials for extra learning opportunity. Results were surprising and revealed a small HI deficit only for the final and most difficult condition, when a delay before test trial was introduced. Study 2 again used the modified radial arm maze, but presented the most difficult condition from the start, and only one daily test trial. Here, results were expected and revealed a robust and consistent HI deficit across all weeks. Combined results indicate that male HI rats can learn a difficult spatial working memory task if it is presented in a graded multi-trial format, but performance is poor and does not appear to remediate if the task is presented with high initial memory demand. Male HI rats in both studies displayed impulsive characteristics throughout testing evidenced as reduced choice latencies despite more errors. This aspect of behavioral results is consistent with impulsiveness as a core symptom of ADHD-a diagnosis common in children with HI insult. Overall findings suggest that task specific behavioral modifications are crucial to accommodating memory deficits in children suffering from cognitive impairments following neonatal HI.

Neonatal/infant validation study of the CAS model 740 noninvasive blood pressure monitor with the Orion/MaxIQ NIBP module.

OBJECTIVE: Blood pressure monitoring is an essential vital sign when caring for critically ill children. Invasive monitoring is considered the gold standard, but is not always feasible. The following study compared the CAS model 740 noninvasive blood pressure monitor with the Orion/MaxIQ NIBP module with the reference (invasive arterial measurement). We evaluated the validity of the system using the criteria provided by the Association for the Advancement of Medical Instrumentation. RESULTS: We performed paired measurements of 29 critically ill neonates and children. For individual paired comparisons, the mean difference in the systolic blood pressure was 2.42 mmHg (SD ± 6.3). The mean difference in the diastolic blood pressure was -1.29 mmHg (SD ± 5.45). The percentage of readings within 5, 10, and 15 mmHg for systolic blood pressure was 65.6, 86.0, and 96.8%, respectively. The percentage of readings within 5, 10, and 15 mmHg for diastolic blood pressure was 77.7, 93, and 95.5%, respectively. CONCLUSION: The CAS model 740 noninvasive blood pressure monitor with the Orion/MaxIQ NIBP module fulfills the accuracy performance criteria of the Association for the Advancement of Medical Instrumentation. This model may allow for rapid and accurate noninvasive blood pressure monitoring in neonates and children.

Sex differences in behavioral outcome following neonatal hypoxia ischemia: insights from a clinical meta-analysis and a rodent model of induced hypoxic ischemic brain injury.

Hypoxia ischemia (HI; reduced oxygen and/or blood flow to the brain) is one of the most common injuries among preterm infants and term infants with birth complications. Both populations show cognitive/behavioral deficits, including impairments in sensory, learning/memory, and attention domains. Clinical data suggests a sex difference in HI outcomes, with males exhibiting more severe cognitive/behavioral deficits relative to matched females. Our laboratory has also reported more severe behavioral deficits among male rats with induced HI relative to females with comparable injury (Hill et al., 2011a,b). The current study initially examined published clinical studies from the past 20years where long-term IQ outcome scores for matched groups of male and female premature infants were reported separately (IQ being the most common outcome measure). A meta-analysis revealed a female "advantage," as indicated by significantly better scores on performance and full scale IQ (but not verbal IQ) for premature females. We then utilized a rodent model of neonatal HI injury to assess sham and postnatal day 7 (P7) HI male and female rats on a battery of behavioral tasks. Results showed expected deficits in HI male rats, but also showed task-dependent sex differences, with HI males having significantly larger deficits than HI females on some tasks but equivalent deficits on other tasks. In contrast to behavioral results, post mortem neuropathology associated with HI was comparable across sex. These findings suggest: 1) neonatal female "protection" in some behavioral domains, as indexed by superior outcome following early injury relative to males; and 2) female protection may entail sex-specific plasticity or compensation, rather than a reduction in gross neuropathology. Further exploration of the mechanisms underlying this sex effect could aid in neuroprotection efforts for at-risk neonates in general, and males in particular. Moreover, our current report of comparable anatomical damage coupled with differences in cognitive outcomes (by sex) provides a framework for future studies to examine neural mechanisms underlying sex differences in cognition and behavior in general.

Therapeutic effect of caffeine treatment immediately following neonatal hypoxic-ischemic injury on spatial memory in male rats.

Hypoxia Ischemia (HI) refers to the disruption of blood and/or oxygen delivery to the brain. Term infants suffering perinatal complications that result in decreased blood flow and/or oxygen delivery to the brain are at risk for HI. Among a variety of developmental delays in this population, HI injured infants demonstrate subsequent memory deficits. The Rice-Vannucci rodent HI model can be used to explore behavioral deficits following early HI events, as well as possible therapeutic agents to help reduce deleterious outcomes. Caffeine is an adenosine receptor antagonist that has recently shown promising results as a therapeutic agent following HI injury. The current study sought to investigate the therapeutic benefit of caffeine following early HI injury in male rats. On post-natal day (P) 7, HI injury was induced (cauterization of the right common carotid artery, followed by two hours of 8% oxygen). Male sham animals received only a midline incision with no manipulation of the artery followed by room air exposure for two hours. Subsets of HI and sham animals then received either an intraperitoneal (i.p.) injection of caffeine (10 mg/kg), or vehicle (sterile saline) immediately following hypoxia. All animals later underwent testing on the Morris Water Maze (MWM) from P90 to P95. Results show that HI injured animals (with no caffeine treatment) displayed significant deficits on the MWM task relative to shams. These deficits were attenuated by caffeine treatment when given immediately following the induction of HI. We also found a reduction in right cortical volume (ipsilateral to injury) in HI saline animals as compared to shams, while right cortical volume in the HI caffeine treated animals was intermediate. These findings suggest that caffeine is a potential therapeutic agent that could be used in HI injured infants to reduce brain injury and preserve subsequent cognitive function.

Infantile hemangiomas and retinopathy of prematurity: possible association.

OBJECTIVE: The goal was to study the clinical association between infantile hemangiomas and retinopathy of prematurity in preterm infants. METHODS: A retrospective study of preterm neonates weighing /=1 cm in size. Univariate analyses showed lower gestational age, lower birth weight, and postnatal steroid use to be predictors of retinopathy of prematurity, whereas prenatal steroid use, race, and gender were not significantly related. In multivariate logistic regression analyses controlling for gestational age and postnatal steroid use, infantile hemangiomas were found to be independently associated with any stage of retinopathy of prematurity. Neither the number nor the size of infantile hemangiomas showed any association with the severity of retinopathy of prematurity. CONCLUSIONS: Infantile hemangiomas are associated with the development of retinopathy of prematurity in infants weighing

Neonatal polycythemia and hyperviscosity.

Neonatal polycythemia and hyperviscosity are defined as a hematocrit > or =65% and a viscosity value >2 standard deviations greater than the norm. Although polycythemia can reflect normal fetal adaptation, it has been thought to be responsible for abnormalities in the neonate. Polycythemia and hyperviscosity are associated with blood-flow changes in some organs, which alter their function. Partial exchange transfusion (PET) has been used to treat both symptomatic and asymptomatic patients. At present, no data support the use of PET in asymptomatic infants; the potential benefit in symptomatic infants depends on the symptoms. Studies of long-term neurodevelopmental status do not show any clear long-term benefits for PET. Crystalloids are as effective as colloids in PET and have the advantage of being cheaper and more readily available; also, they do not confer any risk of infection or anaphylaxis.

Comparisons of mortality and pre-discharge respiratory outcomes in small-for-gestational-age and appropriate-for-gestational-age premature infants.

BACKGROUND: There are differences in the literature regarding outcomes of premature small-for-gestational-age (SGA) and appropriate-for gestational-age (AGA) infants, possibly due to failure to take into account gestational age at birth. OBJECTIVE: To compare mortality and respiratory morbidity of SGA and AGA premature newborn infants. DESIGN/METHODS: A retrospective study was done of the 2,487 infants born without congenital anomalies at 32 wk (OR = 0.41, 95% CI 0.27 - 0.63; p < 0.01). After controlling for GA, SGA infants were observed to be at a significantly higher risk for developing chronic lung disease as compared to AGA infants (OR = 2.2, 95% CI = 1.2 - 3.9, P = 0.01). There was no significant difference between SGA and AGA infants in total days on ventilator. Among infants who survived, mean length of hospital stay was significantly higher in SGA infants born between 26-36 wks GA than AGA infants. CONCLUSIONS: Premature SGA infants have significantly higher mortality, significantly higher risk of developing chronic lung disease and longer hospital stay as compared to premature AGA infants. Even the reduced risk of RDS in infants born at >/=32 wk GA, (conferred possibly by intra-uterine stress leading to accelerated lung maturation) appears to be of transient effect and is counterbalanced by adverse effects of poor intrauterine growth on long term pulmonary outcomes such as chronic lung disease.

Gastroesophageal reflux in infants < 32 weeks gestational age at birth: lack of relationship to chronic lung disease.

The objective of this study was to determine the incidence of gastroesophageal reflux (GER) as documented by extended esophageal pH monitoring in symptomatic premature infants and to identify its relationship with chronic lung disease (CLD). This was a retrospective study of 629 infants born < 32 weeks gestational age and admitted to the neonatal intensive care unit during the study period. Univariate analyses were done on the 137 infants undergoing the test for the association of the following risk factors with acid reflux: birth weight, gestational age, race, sex, length of stay, bronchopulmonary dysplasia (BPD; O2 requirement at 28 days), and severe CLD (O2 requirement at 36 weeks postmenstrual age). Eighty-seven of 137 infants were positive for GER. There was no association of GER with the risk factors studied, nor were there correlations with BPD or severe CLD. GER is common (63%) in premature infants < 32 weeks gestational age but clinical symptoms and CLD are poorly correlated with this diagnosis.

Polycythemia and hyperviscosity in the newborn.

Research from the past 15 to 20 years has led to a comprehensive understanding of the etiology and effects of polycythemia and hyperviscosity in the newborn. Polycythemia and hyperviscosity are generally a result of a poor intrauterine environment or hypoxic complications during labor and delivery. Changes in blood viscosity are a direct result of changes in hematocrit because the plasma viscosity in the newborn is virtually always normal. Polycythemia and hyperviscosity are associated with decreases in blood flow to the brain, heart, lung, intestines, and carcass. Renal blood flow is not affected, but renal plasma flow is diminished, resulting in a lower glomerular filtration rate (GFR). The elevated hemoglobin and hematocrit are associated with an increase in the arterial oxygen content. It is the increase in arterial oxygen content, not the hyperviscosity, that is directly responsible for the decreased blood flow in the brain and heart as well as cardiac output. As a result, brain and cardiac oxygenation is normal. Decreased pulmonary blood flow appears to be the result of hyperviscosity and can result in system hypoxia. This can be corrected by a partial exchange transfusion to lower the hematocrit and viscosity. This will also improve renal function by increasing plasma flow. Because the abnormalities in brain function are due to a primary hypoxia event and not reduced cerebral blood flow, a partial exchange transfusion will not improve short-term or long-term abnormalities in neurological functioning.

Ethical considerations in the management of infants born at extremely low gestational age.

With ongoing improvements in technology and the understanding of neonatal physiology, there has been increasing debate regarding the gestational age and birth weight limits of an infants' capability of sustaining life outside the womb and how this is to be determined. The objective of this review was to address this issue with an analysis of current data (following the introduction of surfactant therapy in 1990) from published studies of survival in extremely low gestational age infants. We found that survival was possible at 22 completed weeks of gestation but only in < 4% of live births reported. Survival increased from 21% at 23 weeks gestational age to 46% at 24 weeks gestational age. Historically, despite continual advances in neonatology, the mortality at 22 weeks has not improved over the past three decades. Combining the data from studies on survival with evidence from developmental biology, we believe that it is not worthwhile to pursue aggressive support of infants born at < 23 weeks gestational age. Given the complicated issues related to morbidity and mortality in infants born at 22 to 25 weeks gestational age and the ethical implications of the available evidence, we propose the need for a consensus derived framework to help in decision-making.

Inguinal hernia in preterm infants (< or = 32-week gestation).

The current incidence of inguinal hernia (IH) in premature infants is not well-established. It is also unclear whether common co-morbidities in this population, i.e., chronic lung disease (CLD) or nutritional status or both contribute to the development of IH. The purpose of this study was to establish the epidemiologic profile of preterm infants of 32 weeks gestational age (GA) or less at birth with IH and determine whether the severity of CLD or poor nutritional status predisposes to the development of IH. Perioperative profiles of infants undergoing surgery were also reviewed. A retrospective study of 1,057 infants born at 23-32 weeks GA from January 1990 to December 1995 was done. Specific risk and demographic factors were identified. Factors used to determine severity of CLD were: days on intermittent mandatory ventilation (IMV); days on positive pressure (IMV + continuous positive airway pressure); and total number of days on supplemental oxygen. Overall nutritional status was determined by weight gain in g/kg per day. The incidence of IH in preterm infants of 32 weeks GA or less who were admitted for 28 days or more was 9.34% (65/696) prior to discharge. The incidence in infants weighing 1,500 g or less was 11.11% (63/567) and in infants 1,000 g or less 17.39% (48/276). All parameters that determined the severity of CLD were statistically significant in infants with IH by univariate analysis. In a multivariate regression model, male gender was the most important variable that was significantly associated with IH (odds ratio OR=9.6; 95% confidence interval CI=3.90-23.59), followed by total days on supplemental oxygen (adjusted OR=1.00; 95% CI= 1.01-1.02). Weight gain (g/kg per day) was not significantly different between the two groups. Surgical correction before discharge was well tolerated. We conclude that the incidence of IH is GA-dependent. Factors related to severity of CLD play a more important role than weight gain in predisposing to IH.

Hypospadias and early gestation growth restriction in infants.

OBJECTIVE: There has been a major increase in the incidence of hypospadias in infants in the 1990s, but the risk factors are not known. Although there are scattered reports in the literature regarding the association of low birth weight and hypospadias, this has not been systematically studied. The objective of this study was to determine the association between early gestation intrauterine growth and hypospadias. METHODS: A retrospective review of 13 years of admissions to 2 tertiary care neonatal intensive care units (NICUs) in Connecticut (1987--2000) showed that 112 (1.66%) of 6746 male infants had any degree of hypospadias. Of these, 8 were part of a genetic syndrome and were excluded. A retrospective cohort analysis of these 6738 infants was performed. Infant growth parameters at birth (weight, head circumference, and length) were analyzed along with maternal risk factors known to be associated with changes in fetal growth, including maternal age, race, diagnosis of preeclampsia, gestational diabetes, and maternal use of alcohol or tobacco or substance abuse during pregnancy. RESULTS: The incidence of hypospadias in the NICU population increased 10-fold from 0.4% in 1987 to 4% in the first quarter of 2000. Hypospadias was significantly more common in infants who had uniformly poor intrauterine growth (<10th percentiles) in the various parameters measured: birth weight, length, or head circumference. There were no significant differences in maternal age or race, nor were there differences in the use of alcohol, tobacco, or street drugs by the mother. There were no differences between singletons and multiple-gestation births. However, the frequency of occurrence was significantly higher among first-born infants (1.9%) compared with all other infants (0.9%). CONCLUSIONS: The incidence of hypospadias in our NICU population has increased 10-fold during the 13-year period of study. There was a significant association of hypospadias with poor intrauterine growth. The growth restriction was probably of early gestational cause as there was proportionate involvement of somatic (weight and length) and brain growth (head circumference). The increasing frequency of hypospadias and its association with poor intrauterine growth originating in early gestation suggests that common environmental factor(s) that have an impact on both conditions may be involved.