The low-birth-weight infant remains at much higher risk of mortality than the infant with normal weight at birth. In the neonatal period, when most infant deaths occur, the proportion of low-birth-weight infants, especially those with very low weight, is the major determinant of the magnitude of the mortality rates. Furthermore, differences in low-birth-weight rates account for the higher neonatal mortality rates observed in some groups, particularly those characterized by socioeconomic disadvantages. Much of the recent decline in neonatal mortality can be attributed to increased survival among low-birth-weight infants, apparently as a result of hospital-based services. The application of these services is currently considered cost-effective, although whether this will continue to be true in the future is unclear because of the increased survival of very tiny infants. Although low-birth-weight infants remain at increased risk of both postneonatal mortality and morbidity in infancy and early childhood, the risk is substantially smaller than that of neonatal death. In addition, these adverse later outcomes have not offset the gains achieved in the neonatal period. Nonetheless, the increased survival of high-risk infants raises concern about their future requirements for special medical and educational services and about the stress on their families. Despite increased access to antenatal services, only moderate declines in the proportion of low-birth-weight infants has been observed, and almost no change has occurred in the proportion of those with very low weight at birth. In addition, in many areas of the country the birth-weight-specific neonatal mortality rates are similar for groups at high and low risk of neonatal death. In view of these findings, continuation of the current decline in neonatal mortality and reduction of the mortality differentials between high- and low-risk groups require the identification and more effective implementation of strategies for the prevention of low-weight births.

High-intensity exercise can result in up to a 1,000-fold increase in the rate of ATP demand compared to that at rest (Newsholme et al., 1983). To sustain muscle contraction, ATP needs to be regenerated at a rate complementary to ATP demand. Three energy systems function to replenish ATP in muscle: (1) Phosphagen, (2) Glycolytic, and (3) Mitochondrial Respiration. The three systems differ in the substrates used, products, maximal rate of ATP regeneration, capacity of ATP regeneration, and their associated contributions to fatigue. In this exercise context, fatigue is best defined as a decreasing force production during muscle contraction despite constant or increasing effort. The replenishment of ATP during intense exercise is the result of a coordinated metabolic response in which all energy systems contribute to different degrees based on an interaction between the intensity and duration of the exercise, and consequently the proportional contribution of the different skeletal muscle motor units. Such relative contributions also determine to a large extent the involvement of specific metabolic and central nervous system events that contribute to fatigue. The purpose of this paper is to provide a contemporary explanation of the muscle metabolic response to different exercise intensities and durations, with emphasis given to recent improvements in understanding and research methodology.

Context Genetic factors play an important role in the etiology of both autism spectrum disorders (ASD) and autistic traits. However, little is known about the etiologic consistency of autistic traits across levels of severity. Objective We compared the etiology of typical variation in autistic traits with extreme scoring groups (including top 1%) which mimicked the prevalence of diagnosed ASD in the largest twin study of autistic traits to date. Design Twin study employing phenotypic analysis and genetic model-fitting in the total sample and extreme scoring groups (top 5%, 2.5%, 1%). Setting A nationally-representative general population twin sample from the United Kingdom. Participants The families of 5,988 12-year-old pairs in the Twin Early Development Study. Main Outcome Measure Autistic traits as assessed by the Childhood Autism Spectrum Test. Results Moderate to high heritability was found for autistic traits in the general population (52% for females; 76% for males). High heritability was found in extreme scoring groups. There were no differences in heritability among extreme groups or between the extreme groups and the general population. A continuous liability shift towards autistic trait affectedness was seen in the cotwins of individuals scoring in the top 1%, suggesting shared etiology between extreme scores and normal variation. Conclusions This evidence of similar etiology across normal variation and the extremes has implications for molecular genetic models of ASD and for conceptualizing ASD as the quantitative extreme of a neurodevelopmental continuum.

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The findings in the HLBW INT group provide support for preschool education to make long-term changes in a diverse group of children who are at developmental risk. The lack of observable benefit in the LLBW group raises questions about the biological and educational factors that foster or inhibit sustained effects of early educational intervention.

Late preterm infants have poorer neurodevelopmental outcomes than term infants and have increased odds to have a mental and/or physical developmental delay.

This sample had double the prevalence of behavior problems expected in the general child population. These problems showed stability over time. Cigarette smoking in pregnancy, maternal psychological distress at 40 weeks' gestation, maternal age, and Hispanic ethnicity all were significant predictors of the development of behavior problems from ages 3 to 8. These findings have implications for health policies on smoking and postnatal depression.

OBJECTIVES The goals of this study were to describe nutritional practices in the first month of life for a large cohort of extremely low gestational age newborns and to determine the impact of these nutritional practices on growth velocity over the same period. METHODS The sample included 1187 infants born at 23 weeks to 27 weeks of gestation, at 14 institutions, between 2002 and 2004. Inclusion criteria included survival until day 28 and weight information for both day 7 and day 28. Growth velocity, expressed as grams per kilogram per day (g/kg/day), was calculated for the interval between days 7 and 28. Nutritional practices during the first week and on days 14, 21, and 28 were compared to current nutritional guidelines in the literature. Multivariable logistic regression models estimated the contribution of limited nutrition to limited growth velocity. RESULTS Protein and fat delivery approximated current nutritional recommendations while carbohydrate and total caloric delivery did not. Despite this, growth velocity of our study infants exceeded the current guideline of 15 g/kg/day. Nevertheless, we found extrauterine growth restriction (i.e., weight for gestational age below the 10th centile) in 75% of infants at 28 days, as compared to only 18% at birth. A growth velocity of 20-30 g/kg/day was associated with infants' maintaining or exceeding their birth weight Z-score, with rates in the upper range for the gestationally youngest infants. Early (day 7) nutritional practices were positively associated with growth velocity measured between days 7 and 28. CONCLUSION The early provision of nutrients is an important determinant of postnatal growth. Extrauterine growth restriction remains high in extremely premature infants even when they achieve a growth velocity rate within current guidelines.