Birth weight and cognitive function in the British 1946 birth cohort: longitudinal population based study

Birth weight and cognitive ability in childhood among siblings and nonsiblings

OBJECTIVES

The purpose of this work was to examine whether the positive association between birth weight and childhood cognitive ability is seen within siblings from the same family, as well as between nonsiblings, and to determine whether these associations vary with age.

METHODS

We compared the association of birth weight with cognitive ability measured at ages 5 to 6, 7 to 9, and 11 to 12 years among a total of 5402 children from different families with that among 2236 to 3083 sibships from the National Longitudinal Study of Youth 1979-Children.

RESULTS

In the whole cohort, there were positive associations between birth weight and cognitive ability at all ages, with the association increasing with age from a 0.81-point increase at ages 5 to 6 years to 1.30 and 1.44 points at ages 7 to 9 and 11 to 12 years, respectively, per 1 SD of gestational age- and gender-adjusted birth weight z score. With adjustment for covariates, there was marked attenuation of these associations. Mean differences were 0.28 points in children aged 5 to 6 years, 0.67 points in those aged 7 to 9 years, and 0.52 points in those aged 11 to 12 years after adjusting for child's gender, race or ethnicity, year of birth, and age at test; maternal age, height, parity, education, smoking during pregnancy, and cognitive ability; and household income. Our family-based analyses that separated within- and between-family effects found that the between-family associations were much stronger than the within-family associations. However, adjustment for potential confounders attenuated the between-family associations, and there was no evidence for a difference in association comparing the between- and within-family associations.

CONCLUSIONS

In these data, the positive association between birth weight and childhood cognitive ability at ages 5 to 12 years is explained largely by family characteristics rather than a specific intrauterine effect.

Population-based cohort studies on premorbid cognitive function in schizophrenia

Many previous studies have found associations between poor cognitive function and schizophrenia. However, the majority of these studies used retrospective data, leading to the possibility of selection and recall biases. Retrospective studies are also unable to distinguish whether cognitive deficits exist prior to the onset of schizophrenia, suggesting that they are important in etiology, or following onset, suggesting that they are secondary to the disorder or its treatment. The current review used a systematic search strategy to identify and summarize the results of all studies that have used population-based cohorts to examine associations between prospectively collected data on premorbid cognitive functioning in childhood or adolescence and subsequent risk for schizophrenia. Three broad categories of study have addressed these questions: birth cohort designs with cognitive testing during childhood, army conscript designs with cognitive performance measured at conscription, and studies using school grades. Birth cohort and conscript studies are consistent in reporting strong associations between poor performance on cognitive batteries and increased risk of schizophrenia. Studies on school performance have been less consistent, although the largest such study showed strong associations across all school subjects. In conclusion, children and adolescents with poor cognitive abilities in childhood are at increased risk of schizophrenia. This suggests that poor cognitive function is either directly causal or associated with causal factors that are involved in etiology.

A life course of adiposity and dementia

Adiposity, commonly measured as body mass index (BMI), may influence or be influenced by brain structures and functions involved in dementia processes. Adipose tissue changes in degree and intensity over the lifespan, and has been shown to influence brain development in relationship to early and late measures of cognitive function, intelligence, and disorders of cognition such as dementia. A lower BMI is associated with prevalent dementia, potentially due to underlying brain pathologies and correspondingly greater rates of BMI or weight decline observed during the years immediately preceding clinical dementia onset. However, high BMI during mid-life or at least approximately 5-10 years preceding clinical dementia onset may increase risk. The interplay of adiposity and the brain occurring over the course of the lifespan will be discussed in relationship to developmental origins, mid-life sequelae, disruptions in brain structure and function, and late-life changes in cognition and dementia. Characterizing the life course of adiposity among those who do and do not become demented enhances understanding of biological underpinnings relevant for understanding the etiologies of both dementia and obesity and their co-existence.

Racial differences in birth outcomes: the role of general, pregnancy, and racism stress

OBJECTIVE

This study examined the role of psychosocial stress in racial differences in birth outcomes.

DESIGN

Maternal health, sociodemographic factors, and 3 forms of stress (general stress, pregnancy stress, and perceived racism) were assessed prospectively in a sample of 51 African American and 73 non-Hispanic White pregnant women.

MAIN OUTCOME MEASURES

The outcomes of interest were birth weight and gestational age at delivery. Only predictive models of birth weight were tested as the groups did not differ significantly in gestational age.

RESULTS

Perceived racism and indicators of general stress were correlated with birth weight and tested in regression analyses. In the sample as a whole, lifetime and childhood indicators of perceived racism predicted birth weight and attenuated racial differences, independent of medical and sociodemographic control variables. Models within each race group showed that perceived racism was a significant predictor of birth weight in African Americans, but not in non-Hispanic Whites.

CONCLUSIONS

These findings provide further evidence that racism may play an important role in birth outcome disparities, and they are among the first to indicate the significance of psychosocial factors that occur early in the life course for these specific health outcomes.

Perinatal outcome and later implications of intrauterine growth restriction

This chapter reviews outcomes for children who have intrauterine growth retardation (IUGR) or small-for-gestation-age (SGA) status at birth. Such infants are at risk for increased perinatal mortality, birth adaptation complications, including perinatal acidosis, hypoglycemia, hypothermia, coagulation abnormalities, and selected immunologic deficiencies. IUGR infants also appear to be at great risk for complications of prematurity, including chronic lung disease and necrotizing enterocolitis. Childhood implications for IUGR include an increased risk for short stature, cognitive delays with decreased academic achievement, and a small but significant increased risk of neurologic disorders, including cerebral palsy. Low socioeconomic status is correlated with the occurrence of IUGR and is significantly related to long-term disabilities. Morbidities associated with preterm delivery appear to be additive to those associated with fetal growth restriction so IUGR, preterm infants may be at great risk for poor neurodevelopmental outcome.

Assessing fetal growth impairments based on family data as a tool for identifying high-risk babies. An example with neonatal mortality

Background

Low birth weight is associated with an increased risk of neonatal and infant mortality and morbidity, as well as with other adverse conditions later in life. Since the birth weight-specific mortality of a second child depends on the birth weight of an older sibling, a failure to achieve the biologically intended size appears to increase the risk of adverse outcome even in babies who are not classified as small for gestation. In this study, we aimed at quantifying the risk of neonatal death as a function of a baby's failure to fulfil its biologic growth potential across the whole distribution of birth weight.

Methods

We predicted the birth weight of 411,957 second babies born in Denmark (1979–2002), given the birth weight of the first, and examined how the ratio of achieved birth weight to predicted birth weight performed in predicting neonatal mortality.

Results

For any achieved birth weight category, the risk of neonatal death increased with decreasing birth weight ratio. However, the risk of neonatal death increased with decreasing birth weight, even among babies who achieved their predicted birth weight.

Conclusion

While a low achieved birth weight was a stronger predictor of mortality, a failure to achieve the predicted birth weight was associated with increased mortality at virtually all birth weights. Use of family data may allow identification of children at risk of adverse health outcomes, especially among babies with apparently "normal" growth.

Infant developmental milestones and subsequent cognitive function

OBJECTIVE

Developmental delay is associated with a subsequent diagnosis of learning disability. However, the relationship between the age of reaching infant developmental milestones and later intellectual function within the general population remains unresolved. We hypothesized that earlier attainment of developmental milestones would be associated with better subsequent intellectual performance throughout the range of abilities, rather than confined to extremes.

METHODS

Developmental data were obtained at age 2 years in the National Survey of Health and Development, a representative sample of 5,362 children born in the United Kingdom in 1946. Data on intellectual function and educational attainment at ages 8, 26, and 53 years were also obtained. Multiple linear regression and logistic regression were used to analyze the effect of age of reaching developmental milestones on subsequent cognition and educational attainment.

RESULTS

The age of reaching developmental milestones was associated with intellectual performance at ages 8, 26, and 53 years; for every month earlier a child learned to stand, there was, on average, a gain of one half of one intelligence quotient point at age 8. Speech development had a small but statistically significant effect on subsequent educational attainment (later developers were less likely to progress beyond basic education); this effect was not apparent for motor development. Effect sizes were reduced when the slowest developers were excluded, but many effects remained significant.

INTERPRETATION

The association between later development and poorer subsequent intellectual function is small, but it does have theoretical implications; we suggest it is secondary to suboptimal cortical-subcortical connectivity.

Associations of birth size, gestational age, and adult size with intellectual performance: evidence from a cohort of Norwegian men

The influences of prenatal and postnatal growth on intellectual performance are unclear. We examined the associations of birth size and gestational age with intellectual performance and explored whether these associations were influenced by adult body size and social factors. In this nationwide cohort study, the records of 317,761 male infants registered in the Medical Birth Registry of Norway (1967-1979) were linked to the Norwegian Conscript Service (1984-1999). The variation in intelligence test score at age 18 due to birth weight and birth length was evaluated using absolute and standardized (z scores) values. Mean intelligence score increased by gestational age, birth weight, and birth length. However, a decline in intellectual performance was observed for gestational age >41 wk and birth weight >4500 g. There was a strong interaction on intellectual performance between birth size and gestational age (p < 0.0005). Adjusting for adult size strongly attenuated the association of birth size with intellectual performance. The overall R of intellectual performance explained by birth size was <1%; however, adding adult body size and social factors to the model increased R to 12%. In conclusion, the association of birth size with intellectual performance was weak, but still present after adjustment for adult body size and social factors.

Newborns at risk for special education placement: a population-based study

OBJECTIVES

To establish the contributions of birth weight (BW), gender, socioeconomic status (SES), and parental age on risks for special education (SE) placements in school-age children.

METHODS

A population-based sample of 900 school-age children attending the following full-time SE groups: at level 1, children had isolated neurodevelopmental, physical, or other impairments; at level 2, borderline to mild intellectual disability (ID); and at level 3, moderate to severe ID. Three hundred and one children enrolled in mainstream education formed the control group (level 0). For all children with siblings, we defined familiar forms of learning disorders as having a sibling in one of the SE groupings. We performed our analysis for the entire cohort as well as comparing risk factors within the familial and non-familial types of SE groupings.

RESULTS

In multinomial logistic regression analysis, age of father 40 years, low BW (<2500g or <-2 SD), male sex, and parent's lower SES, all increased the probability of SE placement. In the familial forms of levels 2 and 3, the parental SES was lower and, in addition, in the level 2, the family size was bigger. Furthermore, in the non-familial form of level 2, both the low and the high (4000g) BW were more common.

CONCLUSIONS

Among the known risk factors for learning disabilities (LD), our study highlighted the importance of a higher paternal age and a lower SES especially in the familial forms of LD.

Association of growth in utero with cognitive function at age 6-8 years

BACKGROUND

Size at birth is associated with later cognitive development. The timing of growth faltering in utero may affect developmental consequences.

AIM

To determine whether growth in utero is related to cognitive outcomes in childhood. A secondary aim was to determine any associations between maternal nutritional status and cognition.

STUDY DESIGN AND SUBJECTS

Subjects were participants in a prospective cohort study of developmental origins of adult disease. Eligible subjects were aged 6-8 years at their next scheduled visit to the study clinic and their mothers had abdominal ultrasound measurements at 14, 25 and 35 weeks gestation. 186 of 264 eligible children attended the clinic and were tested.

OUTCOME MEASURES

Raven's Progressive Matrices (reasoning ability), Peabody Picture Vocabulary Test (receptive vocabulary) and Digit Span Forwards (auditory working memory).

RESULTS

In multiple regression analyses controlling for children's age and socioeconomic status, head circumference at 14 weeks gestation was significantly associated with reasoning ability. The difference between the lowest and highest quartiles was equivalent to 0.4 S.D. No other significant associations with fetal growth were found. Maternal weight gain was not associated with cognitive scores; however, change in triceps skinfold between 25 and 35 weeks gestation was positively associated with reasoning ability and remained a significant predictor when included in the regression model.

CONCLUSIONS

There were few associations between growth in utero and cognition. Growth in head circumference in early gestation and maternal nutrition in late gestation may affect later cognitive ability. Further research in this area is needed to confirm these results.

Global undernutrition during gestation influences learning during adult life

Intrauterine growth restriction can lead to significant long-term health consequences such as metabolic and cardiovascular disorders, but less is known about its effects on choice and behavioral adaptation in later life. Virgin Wistar rats were time mated and randomly assigned to receive either ad-libitum access to chow or 30% of that level of nutrition during pregnancy to generate growth-restricted offspring. At 60 days of age, 6 female offspring from each group were trained on concurrent variable-interval schedules. Sessions consisted of seven randomly arranged concurrent-schedule components, each with a different reinforcer ratio that varied from 27:1 to 1:27, and each component lasting for 10 reinforcer deliveries. Behavioral change across reinforcers in components, measured by sensitivity to reinforcement, was consistently lower for offspring of undernourished mothers, showing that their behavior was less adaptable to environmental change. These results provide direct experimental evidence for a link between prenatal environmental conditions and reduced behavioral adaptability--learning--in later life.

Clinical versus sonographic estimation of foetal weight in southwest Nigeria

A prospective study was conducted at Obafemi Awolowo University Teaching Hospital Complex, Ile-Ife, Nigeria, between 3 January and 31May 2004, to compare the accuracy of clinical and ultrasonographic estimation of foetal weight at term. One hundred pregnant women who fulfilled the inclusion criteria had their foetal weight estimated independently using clinical and ultrasonographic methods. Accuracy was determined by percentage error, absolute percentage error, and proportion of estimates within 10% of actual birth-weight (birth-weight of +10%). Statistical analysis was done using the paired t-test, the Wilcoxon signed-rank test, and the chi-square test. The study sample had an actual average birth-weight of 3,255+622 (range 2,150-4,950) g. Overall, the clinical method overestimated birth-weight, while ultrasound underestimated it. The mean absolute percentage error of the clinical method was smaller than that of the sonographic method, and the number of estimates within 10% of actual birth-weight for the clinical method (70%) was greater than for the sonographic method (68%); the difference was not statistically significant. In the low birth-weight (<2,500 g) group, the mean errors of sonographic estimates were significantly smaller, and significantly more sonographic estimates (66.7%) were within 10% of actual birth-weight than those of the clinical method (41.7%). No statistically significant difference was observed in all the measures of accuracy for the normal birth-weight range of 2,500-<4,000 g and in the macrosonic group (> or =4,000 g), except that, while the ultrasonographic method underestimated birth-weight, the clinical method overestimated it. Clinical estimation of birth-weight is as accurate as routine ultrasonographic estimation, except in low-birth-weight babies. Therefore, when the clinical method suggests weight smaller than 2,500 g, subsequent sonographic estimation is recommended to yield a better prediction and to further evaluate foetal well-being.

To catch up or not to catch up: is this the question? Lessons from animal models

PURPOSE OF REVIEW

Low birth weight and accelerated postnatal catch-up growth during early life are independent risk factors for adult disease, including diabetes, obesity, and cardiovascular disease. As they are intimately linked, it is difficult to determine the independent contributions of birth weight and catch-up growth per se. This review focuses on evidence derived from animal models of disease, in which it is possible to dissect more clearly the independent roles of intrauterine growth retardation, low birth weight, and catch-up growth in mediating disease risk.

RECENT FINDINGS

Recent data from rats, mice and birds show that accelerated postnatal growth is a trigger for the development of adult disease and, ultimately, can affect longevity.

SUMMARY

Understanding the mechanisms and relative contribution of low birth weight and early postnatal catch-up growth to late onset of disease is critical to establish appropriate interventions to prevent or delay adult disease.

The relationship between birthweight, weight gain in infancy, and educational attainment in childhood

Previous studies have examined the relationship between low weight gain (failure to thrive) in infancy and later cognitive ability, but no study to date appears to have examined the relationship between weight gain in infancy across the 'normal' range and later cognitive ability. We report results for a large prospective birth cohort of the relationship between weight gain in infancy and educational attainment at age 10. Routinely recorded weights from child health clinic records for an annual birth cohort of 3418 children born with gestation >36 weeks were collected, as well as gestation in weeks, birthweight and the postcode, for which the Townsend Deprivation Score was identified. At 10 years of age, those attending schools within the Newcastle Education Authority were given a picture vocabulary and a non-verbal ability test, and tests of educational attainment in maths and reading. These were successfully linked to the infant weight data for 2294 (63%) of the children, and complete growth data were available for 1724 (47%) of the children who had completed at least one educational test. There was a significant positive relationship between weight gain in infancy and picture vocabulary, adjusted for economic deprivation, gestational age and birthweight, but not with any of the other outcomes. There was a statistically significant association between birthweight and all four outcomes, which was positive up to about one SD above average birthweight, and negative above. In this population, the association between early growth and cognitive outcomes is stronger for growth before birth, postnatal weight gain having a relatively minor impact.

Premorbid (early life) IQ and later mortality risk: systematic review

PURPOSE

Studies of middle-aged and particularly older-aged adults found that those with higher scores on tests of IQ (cognitive function) had lower rates of later mortality. Interpretation of such findings potentially is hampered by the problem of reverse causality: such somatic diseases as diabetes or hypertension, common in older adults, can decrease cognitive function. Studies that provide extended follow-up of the health experience of individuals who had their (premorbid) IQ assessed in childhood and/or early adulthood minimize this concern. The purpose of the present report is to systematically locate, evaluate, and interpret the findings of all such studies.

METHODS

We systematically identified individual-level studies linking premorbid IQ with later mortality by using four approaches: search of electronic databases (MEDLINE, EMBASE, and PSYCHINFO); scrutiny of the reference sections of identified reports; search of our own files; and contact with researchers in the field. Study quality was assessed by using predefined criteria.

RESULTS

Nine cohort studies met the inclusion criteria. Overall, study quality was moderate. All reports showed an inverse IQ-mortality relation; i.e., higher IQ scores were associated with decreased mortality risk. The nature of this relation (i.e., dose-response or threshold) and whether it differs by sex was unclear. The IQ-mortality association did not appear to be explained by reverse causality or selection bias. Confounding by other early-life factors also did not seem to explain the association, although some studies were not well characterized in this regard. Adult socioeconomic position appeared to mediate the IQ-mortality association in some studies, but this was not a universal finding.

CONCLUSIONS

In all studies, higher IQ in the first two decades of life was related to lower rates of total mortality in middle to late adulthood. Some plausible mechanistic pathways exist, but further examination is required. The precise nature of the IQ-mortality relation (particularly in ethnic minorities and women) and the link between IQ and disease-specific outcomes also warrants further research.

Compensatory growth impairs adult cognitive performance

Several studies have demonstrated that poor early nutrition, followed by growth compensation, can have negative consequences later in life. However, it remains unclear whether this is attributable to the nutritional deficit itself or a cost of compensatory growth. This distinction is important to our understanding both of the proximate and ultimate factors that shape growth trajectories and of how best to manage growth in our own and other species following low birth weight. We reared sibling pairs of zebra finches on different quality nutrition for the first 20 d of life only and examined their learning performance in adulthood. Final body size was not affected. However, the speed of learning a simple task in adulthood, which involved associating a screen colour with the presence of a food reward, was negatively related to the amount of growth compensation that had occurred. Learning speed was not related to the early diet itself or the amount of early growth depression. These results show that the level of compensatory growth that occurs following a period of poor nutrition is associated with long-term negative consequences for cognitive function and suggest that a growth-performance trade-off may determine optimal growth trajectories.

The speed with which adult zebra finches learned a new association task inversely correlates not with the degree of nutritional deprivation experienced early in life, but with the level of compensatory growth.

Health selection and the process of social stratification: the effect of childhood health on socioeconomic attainment

This study investigates whether childhood health acts as a mechanism through which socioeconomic status is transferred across generations. The study uses data from the Panel Study of Income Dynamics to track siblings and to estimate fixed-effects models that account for unobserved heterogeneity at the family level. The results demonstrate that disadvantaged social background is associated with poor childhood health. Subsequently, poor health in childhood has significant, direct, and large adverse effects on educational attainment and wealth accumulation. In addition, childhood health appears to have indirect effects on occupational standing, earnings, and wealth via educational attainment and adult health status. The results further show that socioeconomic health gradients are best understood as being embedded within larger processes of social stratification.

Comparing individual- and area-based socioeconomic measures for the surveillance of health disparities: A multilevel analysis of Massachusetts births, 1989-1991

The absence of individual-level socioeconomic information in most US health surveillance data necessitates using area-based socioeconomic measures (ABSMs) to monitor health inequalities. Using the 1989-1991 birth weight data from Massachusetts, the authors compared estimates of health disparities detected with census tract- and block group-level ABSMs pertaining to poverty and education, as well as parental education, both independently and together. In separate models, adjusted for infant's sex, mother's age, and parents' race/ethnicity, worst-off categories of census tract ABSMs and parental education had a comparable birth weight deficit of approximately 70 g. Similar results were observed for low birth weight (<2,500 g), with worst-off categories of census tract ABSMs and parental education having an odds ratio of approximately 1.37 (p < 0.001). In mutually adjusted models for birth weight and low birth weight, census tract ABSMs still detected an effect estimate nearly 50% of that detected by parental education. Additionally, census tract ABSMs detected socioeconomic gradients in birth weight among births to mothers aged less than 25 years, an age group in which educational attainment is unlikely to be completed. These results suggest that aptly chosen ABSMs can be used to monitor socioeconomic inequalities in health. The risk, if any, in the absence of individual-level socioeconomic information is a conservative estimate of socioeconomic inequalities in health.

Determinants of birthweight inequalities: population-based study

BACKGROUND

The aim of this paper is to study the whole spectrum of birthweight in a population-based birth cohort in order to document the role played by social factors, which complement physiological and behavioural factors, in the development of birthweight inequalities at the population level.

METHODS

The analyses were performed with data from the 'Quebec Longitudinal Study of Child Development 1998-2002 (QLSCD)'. The study follows a representative sample (n = 2103) of the children born in 1998 in the Canadian province of Québec.

RESULTS

Multivariate analyses adjusted for gestational age and mother's age indicate that mean birthweight was higher for boys than girls; improved with birth rank, mother's body mass index (BMI), and family socioeconomic status; and was lower for children of smoking mothers. Compared with children born to non-smoking mothers of higher socioeconomic status, the odds of having a low birthweight were between 6 and 12 times higher for children born to smoking mothers of lower or middle socioeconomic status. When maternal smoking status and mother's BMI are combined, socioeconomic status could still be seen to have a positive effect on mean birthweight except for overweight or obese smoking mothers, among whom the relationship between socioeconomic status and mean birthweight was reversed. In families of lower socioeconomic status, maternal smoking was the most important factor in birthweight inequalities, and in families of higher socioeconomic status, mother's BMI was the most important factor in birthweight inequalities.

CONCLUSION

This research is not only important for children in developed nations, but also for those in developing countries, where high birthweight and obesity are becoming more prevalent.

Gestational age and birth weight in relation to school performance of 10-year-old children: a follow-up study of children born after 32 completed weeks

BACKGROUND

Children born extremely premature (<28 weeks) or with a very low birth weight (<1500 g) have a poorer school performance than children born at term with a normal birth weight. Much less is known about children of higher gestational ages and birth weights. We studied gestational age after 32 completed weeks and birth weight in relation to the child's school performance at the age of 10 years.

METHODS

We performed a follow-up study of 5319 children born between January 1990 and June 1992. We got the information on birth weight and gestational age from birth registration forms; when the children were between 9 and 11 years of age, we gathered information about their school performance (reading, spelling, and arithmetic) from questionnaires completed by the parents and the children's primary school teachers.

RESULTS

The association between birth weight and reading, as well as spelling and arithmetic disabilities, showed a graded relationship, with children who weighed <2500 g having the highest risks. Even children who weighed between 3000 and 3499 g had an increased risk of all 3 learning disabilities compared with children who weighed between 3500 and 4000 g. This association persisted after adjustment for potential cofounders and when the analyses were restricted to children born at term (39-40 weeks of gestation), suggesting that the association could not be explained by a low gestational age. Compared with children born at term, reading and spelling difficulties were more often found among children born at gestational age 33 to 36 weeks and 37 to 38 weeks, whereas there was no relation between gestational age and arithmetic difficulties.

CONCLUSIONS

Gestational age and birth weight were associated with school performance in the 10-year-old child and the association extended into the reference range of both birth weight and gestational age.

Early-life risk factors for Alzheimer disease

Research findings obtained over the past 20 years suggest that Alzheimer disease (AD) may have its origins in early life. In this review, we consider the evidence for early-life risk factors for this illness. We propose that risk factors that predict neuropathology are largely distinct from those related to the clinical expression of Alzheimer disease. Early-life risk factors for pathology include genes, chromosomal abnormalities, head injury, insulin resistance, and inflammation. With regard to risk factors for clinical expression of Alzheimer disease, six general groups of childhood exposures are reviewed: (1) perinatal conditions, (2) early-life brain development, (3) early-life body growth, (4) early-life socioeconomic conditions, (5) environmental enrichment, and (6) cognitive reserve. The literature reviewed suggests that risk of Alzheimer disease is probably not determined in any single time period but results from the complex interplay between genetic and environmental exposures throughout the life course. Enhancement or preservation of brain or cognitive reserve could delay the onset of Alzheimer disease and in some cases prevent the disease from occurring altogether.

The Relative Effect of Size at Birth, Postnatal Growth and Social Factors on Cognitive Function in Late Childhood

PURPOSE

To investigate if fetal, head, and somatic postnatal growth are independent predictors of cognition and estimate their relative importance compared to the effect size of social factors on cognitive function at 10 years.

METHODS

Longitudinal population-based data from the birth questionnaire and the 5- and 10-year sweeps of the 1970 British Birth Cohort Study were used, including 11,244 subjects. Multiple linear regression and structural equation modeling were used in the statistical analysis. Standardized coefficients were used to measure and compare effect sizes.

RESULTS

Fetal growth, head, and somatic postnatal growth were significant independent predictors of cognition at age 10. These associations remained even among children born within the normal birth-weight range and those who did not experience neonatal problems. Effect of head size on cognition was greater than the effect of birth weight. Weight at 10 had a small negative effect on cognition. Gestational age was not directly associated with cognitive function, but it had a weak indirect effect. Parent's socioeconomic status was strongly associated with child's cognitive function.

CONCLUSION

Although effect sizes of prenatal and postnatal growth on cognition are modest compared with the strong effect size of social factors, they might have greater impact at the population level, since most children are born without low birth weight.

Outcomes in adulthood for children with foetal growth retardation. A linkage study from the Nord-Trøndelag Health Study (HUNT) and the Medical Birth Registry of Norway

OBJECTIVE

The aims were to examine the long-term functional outcome and risk of mood disorders in adulthood in individuals with foetal growth retardation.

METHOD

In a prospective cohort study of 7806 individuals aged 20-30 years, using linked data from the Health Survey of Nord-Trøndelag (HUNT-2) and the Medical Birth Registry of Norway, we studied the long-term effects of being born with a birth weight below the 10th percentile for gestational age (SGA).

RESULTS

SGA individuals had lower educational level (OR: 1.33), lower socioeconomic functioning level (OR: 1.77) and more frequent reported mood disorder in adulthood (OR: 1.26). Analyses of a substratum of infants born at term showed almost identical results.

CONCLUSION

Foetal growth retardation measured as SGA shows a moderate risk for lower education and socioeconomic level and for anxiety and/or depression in young adulthood. Issues concerning interventions for children at risk should be considered.

Fetal growth and childhood behavioral problems: results from the ALSPAC cohort

Using data on 4,813 children from the ALSPAC cohort in Bristol, United Kingdom, recontacted in 1998-1999, the authors investigated whether intrauterine growth restriction (indexed by birth weight and length) was associated with behavioral problems at age 7 years. Childhood behavioral problems were measured by using a brief behavioral screening questionnaire (the Strengths and Difficulties Questionnaire (parental completion)). For term singleton infants, a one standard deviation increase in birth weight was associated with an 11% reduction in the odds of behavioral problems at age 81 months. After adjustment for confounders and birth length, this association was no longer seen. The association with birth length remained after adjustment for confounders. A one standard deviation increase in birth length was associated with a 14% decrease in the odds of being in the top tertile of total behavioral difficulties at age 81 months (odds ratio = 0.86, 95% confidence interval: 0.79, 0.95) and was similarly associated with hyperactivity and conduct problems. Evidence was weak for an association between birth length and behavioral problems earlier in childhood. In summary, there was a weak association between intrauterine growth restriction, indexed by birth length (rather than weight), and childhood behavioral problems. Future work should focus on elucidating the biologic mechanisms that lead to variations in birth length and underlie this association.

Modes of imprinted gene action in learning disability

BACKGROUND

It is now widely acknowledged that there may be a genetic contribution to learning disability and neuropsychiatric disorders, stemming from evidence provided by family, twin and adoption studies, and from explicit syndromic conditions. Recently it has been recognized that in some cases the presentation of genetic syndromes (or discrete aspects of disorders) is dependent on the sex of the transmitting parent. Such 'parent-of-origin effects' can be explained by a number of genetic mechanisms, a predominant one of which is genomic imprinting. Genomic imprinting refers to the parent of origin-specific epigenetic marking of an allele of a gene, such that for some genes it is mainly the maternally inherited allele only that is expressed, whereas for others expression occurs mainly from the paternal copy.

METHODS

Here we discuss the contribution of imprinted genes to mental dysfunction and learning disability, using clinical examples of association studies and explicit imprinting disorders (with particular emphasis to Angelman and Prader-Willi syndromes), and evidence from animal work.

RESULTS

Clinical and animal studies strongly suggest that imprinted genes contribute to brain functioning, and when the genes or epigenetic processes are disrupted, this can give rise to neuropsychiatric problems. Another system to which imprinted genes provide a large contribute is the placenta and foetal development. Epidemiological studies suggest that this is also a key area in which dysregulation can give rise to learning difficulties.

CONCLUSIONS

Disruption of imprinted genes, or the epigenetic processes controlling them, can contribute to learning disability. These effects can be divided into two types: direct effects, such as those seen in explicit imprinting disorders such as Angelman and Prader-Willi syndromes, and indirect effects as manifest via changes in foetal programming.

Feeding preterm infants after hospital discharge: a commentary by the ESPGHAN Committee on Nutrition

Survival of small premature infants has markedly improved during the last few decades. These infants are discharged from hospital care with body weight below the usual birth weight of healthy term infants. Early nutrition support of preterm infants influences long-term health outcomes. Therefore, the ESPGHAN Committee on Nutrition has reviewed available evidence on feeding preterm infants after hospital discharge. Close monitoring of growth during hospital stay and after discharge is recommended to enable the provision of adequate nutrition support. Measurements of length and head circumference, in addition to weight, must be used to identify those preterm infants with poor growth that may need additional nutrition support. Infants with an appropriate weight for postconceptional age at discharge should be breast-fed when possible. When formula-fed, such infants should be fed regular infant formula with provision of long-chain polyunsaturated fatty acids. Infants discharged with a subnormal weight for postconceptional age are at increased risk of long-term growth failure, and the human milk they consume should be supplemented, for example, with a human milk fortifier to provide an adequate nutrient supply. If formula-fed, such infants should receive special postdischarge formula with high contents of protein, minerals and trace elements as well as an long-chain polyunsaturated fatty acid supply, at least until a postconceptional age of 40 weeks, but possibly until about 52 weeks postconceptional age. Continued growth monitoring is required to adapt feeding choices to the needs of individual infants and to avoid underfeeding or overfeeding.

Effect of iron supplementation during pregnancy on birthweight: evidence from Zimbabwe

BACKGROUND

Iron deficiency in pregnant women has been shown to reduce the oxygen supply to the fetus, cause intrauterine growth retardation, and increase the risk of premature delivery and reduced birthweight. Yet the effects of iron supplementation programs on pregnancy outcomes are not well documented for developing countries.

OBJECTIVE

To examine the relation between iron supplementation of mothers during pregnancy and children's birthweight using data from a national population-based survey in Zimbabwe.

METHODS

The analysis uses information on 3559 births during the five years preceding the 1999 Zimbabwe Demographic and Health Survey. The effect of iron supplementation during pregnancy on birthweight was estimated by multiple regression, controlling for potential confounding effects of prenatal care, child's sex and birth order, mother's education and nutritional status (measured by body-mass index), household living standard, smoke exposure, and other variables.

RESULTS

Babies born to mothers who received iron supplementation during pregnancy were 103 g heavier (95% confidence interval, 42-164; p = .001), on average, than babies born to mothers who did not receive iron supplementation during pregnancy. The difference was 64 g (95% confidence interval, 2-125; p = .043) for children whose birthweights were taken from health cards and 163 g (95% confidence interval, 44-281; p = .008) for children whose birthweights were reported by their mothers.

CONCLUSIONS

Iron supplementation during pregnancy is associated with significantly higher birthweight, independent of other pregnancy care factors, mother's nutritional status, smoke exposure, and a number of demographic and socioeconomic factors. Prenatal iron supplementation programs can improve pregnancy outcomes and promote child survival in developing countries.

Birthweight and cognitive development during childhood

OBJECTIVES

Low birthweight has been reported to be associated with lower IQ at school age. Further, some evidence suggests that the association extends across the range of normal birthweights. This study assessed the relationship of birthweight to cognitive development in the Port Pirie birth cohort.

METHODS

Of 723 singleton live births recruited into a prospective birth cohort study, 601, 548, 494 and 375 children were followed at ages 2, 4, 7 and 11-13 years, respectively. The children's developmental status was assessed using the Bayley Scales of Infant Development at age 2 years, the McCarthy Scales of Children's Abilities at age 4 years, and the revised Wechsler Intelligence Scale for Children at ages 7 and 11-13 years. The association between birthweight and cognitive function was assessed with multiple linear regression, adjusting for a wide range of possible confounders.

RESULTS

The mean birthweight was 3386 g (SD: 517). There was a statistically significant association between birthweight and cognitive performance at age 2 years (adjusted deficit: 0.97 points per 100 g lighter; 95% CI: 0.4-1.5), but the magnitude of this association gradually decreased and became statistically non-significant at later childhood.

CONCLUSIONS

The relationship between birthweight and cognitive development becomes progressively attenuated at increasing age. At older ages, socioenvironmental factors appear to play an increasingly important part in children's cognitive development.

Risks for low intellectual performance related to being born small for gestational age are modified by gestational age

OBJECTIVE

We sought to study whether the association between being born small for gestational age and risk for low intellectual performance was modified by gestational age.

METHODS

A population-based cohort study was conducted of 352,125 boys who were born between 28 and 43 completed weeks of gestation from 1973 to 1981 in Sweden. Risk for low intellectual performance at military conscription, estimated as odds ratios with 95% confidence intervals was measured.

RESULTS

Compared with men who were born preterm (28-36 weeks) and had normal birth weight for gestational age, men who were born preterm and had a very low birth weight for gestational age were not at increased risk for low intellectual performance. In contrast, men who were born preterm with a very short birth length or a very small head circumference for gestational age faced a near doubled risk for low intellectual performance compared with their appropriate peers. Among men who were born at term (37-41 weeks), risk for low intellectual performance was increased among those with very or moderately small birth weight, birth length, or head circumference for gestational age.

CONCLUSIONS

During early stages of gestation, growth in length and head circumference may be more important for intellectual development than weight increase. Future studies on size at birth and intellectual performance should consider also including anthropometric measurements other than birth weight.

Early life predictors of childhood intelligence: findings from the Mater-University study of pregnancy and its outcomes

Growing evidence linking childhood intelligence with adult health outcomes suggests a need to identify predictors of this psychological characteristic. In this study, we have examined the early life determinants of childhood intelligence in a population-based birth cohort of individuals born in Brisbane, Australia between 1981 and 1984. In univariable analyses, family income in the year of birth, maternal and paternal education, maternal age at birth, maternal ethnicity, maternal smoking during pregnancy, duration of labour, birthweight, breast feeding and childhood height, and body mass index were all associated with intelligence at age 14. In multivariable analyses, the strongest and most robust predictors of intelligence were family income, parental education and breast feeding, with these three variables explaining 7.5% of the variation in intelligence at age 14. Addition of other variables added little further explanatory power. Our results demonstrate the importance of indicators of socio-economic position as predictors of intelligence, and illustrate the need to consider the role of such factors in generating the association of childhood intelligence with adult disease risk.

A life-course approach to the aetiology of late-onset dementias

Substantial progress has been made in the understanding of the neurobiology of dementias, but comprehensive causal models are not available. Genetic and environmental factors probably interact to determine vulnerability to the dementias. The life-course approach to age-related diseases, when systematically applied to the dementias, provides opportunities to identify the nature and timing of environmental contributions. We discuss the relevance of the fetal origins of adult disease hypothesis to the dementias. Associations between the dementias (most often described as Alzheimer's disease) and ischaemic heart disease, obesity, hypertension, hyperlipidaemia, and non-insulin-dependent diabetes mellitus are set against associations between dementias and childhood intelligence, low educational attainments, low socioeconomic status, occupation, and lifetime dietary history. Biological mechanisms that explain how fetal development might influence the risk of adult disease may be relevant to many age-related diseases including the dementias and, possibly, to the biology of ageing.

Season of birth is associated with anthropometric and neurocognitive outcomes during infancy and childhood in a general population birth cohort

The 'season of birth' effect is one of the most consistently replicated associations in schizophrenia epidemiology. In contrast, the association between season of birth and development in the general population is relatively poorly understood. The aim of this study was to explore the impact of season of birth on various anthropometric and neurocognitive variables from birth to age seven in a large, community-based birth cohort. A sample of white singleton infants born after 37 weeks gestation (n = 22,123) was drawn from the US Collaborative Perinatal Project. Anthropometric variables (weight, head circumference, length/height) and various measures of neurocognitive development, were assessed at birth, 8 months, 4 and 7 years of age. Compared to summer/autumn born infants, winter/spring born infants were significantly longer at birth, and at age seven were significantly heavier, taller and had larger head circumference. Winter/spring born infants were achieving significantly higher scores on the Bayley Motor Score at 8 months, the Graham-Ernhart Block Test at age 4, the Wechsler Intelligence Performance and Full Scale scores at age 7, but had significantly lower scores on the Bender-Gestalt Test at age 7 years. Winter/spring birth, while associated with an increased risk of schizophrenia, is generally associated with superior outcomes with respect to physical and cognitive development.

Teenage children of teenage mothers: psychological, behavioural and health outcomes from an Australian prospective longitudinal study

In many industrialised countries teenage pregnancy and teenage parenthood have in recent years been identified as social and public health problems that need to be tackled. A number of studies have looked at various outcomes for teenage mothers and their offspring, and many report a strong association with poverty for the mother both before and after having a child. Few studies, however, adequately control for socioeconomic circumstances when examining health and related outcomes. Most studies have focused on perinatal outcomes in the offspring with few looking at later health and development. In Australia, where the rate of teenage pregnancy is relatively high compared to other comparable countries, teenage pregnancy is a not prominent policy concern. As such, Australia offers the opportunity to study the outcomes of teenage parenthood in a country where there may be less stigma than in countries that portray teenage parenthood as a major health and/or social problem. This paper reports findings from the Mater-University Study of Pregnancy (MUSP) and its outcomes, a prospective study of women, and their offspring, who received antenatal care at a major public hospital (Mater Misericordiae Hospital) in South Brisbane, Australia, between 1981 and 1984. We have examined the associations of maternal age (< or =18 years (n=460) versus >18 years (n=4800)) at first antenatal visit with offspring psychological, behavioural and health characteristics when the offspring--the teenage children of teenage mothers--were aged 14 years. Multiple logistic regression was used to determine the effect of maternal and family characteristics on associations between maternal age and childhood outcomes at age 14. Results show that the 14 year old offspring of mothers who were aged 18 years and younger compared to those who were offspring of older mothers were more likely to have disturbed psychological behaviour, poorer school performance, poorer reading ability, were more likely to have been in contact with the criminal justice system and were more likely to smoke regularly and to consume alcohol. However, maternal age was not associated with health outcomes in their offspring at age 14 years. Indicators of low socioeconomic position and maternal depression were also associated with poorer psychological, cognitive and behavioural outcomes among 14 year olds. In addition children from poorer socioeconomic backgrounds and whose mothers were depressed were more likely to have self-reported poor health, asthma, to have been admitted to hospital twice or more since birth and to be bed-wetters at age 14. The associations between maternal age and psychological distress, school performance, and smoking and alcohol use were all largely explained by socioeconomic factors, maternal depression, family structure and maternal smoking. These findings confirm that not all teenage mothers and their offspring have adverse outcomes, and that many if not the majority have good outcomes.

Childhood intelligence in relation to adult coronary heart disease and stroke risk: evidence from a Danish birth cohort study

While recent studies have reported an inverse relation between childhood intelligence test scores and all-cause mortality in later life, the link with disease-specific outcomes has been rarely examined. Furthermore, the potential confounding effect of birthweight and childhood social circumstances is unknown. We investigated the relation of childhood intelligence with coronary heart disease (CHD) and stroke risk in a cohort of 6910 men born in 1953 in the Copenhagen area of Denmark. Events were ascertained from 1978 to 2000 using a cause-of-death register and hospital discharge records. There were 150 CHD (19 fatal; 131 non-fatal) and 93 stroke (4 fatal; 89 non-fatal) events during follow-up into mid-life. Childhood intelligence was inversely related to CHD with the highest rate apparent in adults with low childhood test scores (HR(lowest vs. highest quartile), 2.70; 95% confidence interval: 1.60, 4.57; P(trend) = 0.0001). After adjustment for paternal social class and birthweight, this association was attenuated only marginally. There was little evidence of a IQ-stroke relationship. The cognitive characteristics captured by IQ testing in the present study, such as communication and problem solving ability, appear to be associated with risk of CHD. Health promotion specialists and clinical practitioners may wish to consider these skills in their interactions with the general public. Replication of these results using studies which hold data on intelligence and socio-economic position across the life course is required.

Association of insulin-like growth factor I and insulin-like growth factor-binding protein-3 with intelligence quotient among 8- to 9-year-old children in the Avon Longitudinal Study of Parents and Children

BACKGROUND

Insulin-like growth factor I (IGF-I) is a hormone that mediates the effects of growth hormone and plays a critical role in somatic growth regulation and organ development. It is hypothesized that it also plays a key role in human brain development. Previous studies have investigated the association of low IGF-I levels attributable to growth hormone receptor deficiency with intelligence but produced mixed results. We are aware of no studies that investigated the association of IGF-I levels with IQ in population samples of normal children.

OBJECTIVES

To investigate the association of circulating levels of IGF-I and its principle binding protein, IGF-binding protein-3 (IGFBP-3), in childhood with subsequent measures of IQ.

METHODS

The cohort study was based on data for 547 white singleton boys and girls, members of the Avon Longitudinal Study of Parents and Children, with IGF-I and IGFBP-3 measurements (obtained at a mean age of 8.0 years) and IQ measured with the Wechsler Intelligence Scale for Children (at a mean age of 8.7 years). We also investigated associations with measures of speech and language based on the Wechsler Objective Reading Dimensions test (measured at an age of 7.5 years) and the Wechsler Objective Language Dimensions test (listening comprehension subtest only, measured at an age of 8.7 years). For some children (n = 407), IGF-I (but not IGFBP-3) levels had been measured at approximately 5 years of age in a previous study. Linear regression models were used to investigate associations of the IGF-I system with the measures of cognitive function.

RESULTS

Three hundred one boys and 246 girls were included in the sample. IGF-I levels (mean +/- SD) were 142.6 +/- 53.9 ng/mL for boys and 154.4 +/- 51.6 ng/mL for girls. IQ scores (mean +/- SD) were 106.05 +/- 16.6 and 105.27 +/- 15.6 for boys and girls, respectively. IGF-I levels were associated positively with intelligence. For every 100 ng/mL increase in IGF-I, IQ increased by 3.18 points (95% confidence interval [CI]: 0.52 to 5.84 points). These positive associations were seen in relation to the verbal component (coefficient: 4.27; 95% CI: 1.62 to 6.92), rather than the performance component (coefficient: 1.06; 95% CI: -1.67 to 3.78), of IQ. There was no evidence that associations with overall IQ differed between boys and girls. In a data set with complete information on confounders (n = 484), controlling for birth weight (adjusted for gestation), breastfeeding, and BMI slightly strengthened the associations of IGF-I levels with IQ. Additionally controlling for maternal education and IGFBP-3 levels attenuated the associations (change in IQ for every 100 ng/mL increase in IGF-I levels: 2.51 points; 95% CI: -0.42 to 5.44 points). The weakening of associations in models controlling for markers of parental socioeconomic position and education could reflect shared influences of parental IGF levels on parents' own educational attainment and their offspring's IGF-I levels. In unadjusted models examining associations of Wechsler Objective Reading Dimensions and Wechsler Objective Language Dimensions test scores with IGF-I levels, there was no strong evidence that performance on either of these tests was associated with circulating IGF-I levels, although positive associations were seen with both measures. Associations between IGF-I levels measured at age 5 and Wechsler Intelligence Scale for Children scores (n = 407) were similar to those for IGF-I levels measured at age 7 to 8. For every 100 ng/mL increase in IGF-I levels at 5 years of age, IQ increased by 2.3 points (95% CI: -0.21 to 4.89 points).

CONCLUSIONS

This study provides some preliminary evidence that IGF-I is associated with brain development in childhood. Additional longitudinal research is required to clarify the role of IGF-I in neurodevelopment. Because IGF-I levels are modifiable through diet and other environmental exposures, this may be one pathway through which the childhood environment may influence neurodevelopment.

Early life predictors of childhood intelligence: evidence from the Aberdeen children of the 1950s study

OBJECTIVE

To identify the early life predictors of childhood intelligence.

DESIGN

Cohort study of 10 424 children who were born in Aberdeen (Scotland) between 1950 and 1956.

RESULTS

Social class of father around the time of birth, gravidity, maternal age, maternal physical condition, whether the child was born outside of marriage, prematurity, intrauterine growth, and childhood height were all independently associated with childhood intelligence at ages 7, 9, and 11. The effect of social class at birth was particularly pronounced, with a graded linear association across the distribution even with adjustment for all other covariates (p<0.001 for linear trend). Those from the lowest social class (V) had intelligence scores that were on average 0.9-1.0 of a standard deviation lower than those from the higher groups (I and II) at each of the three ages of intelligence testing. Collectively, the early life predictors that were examined explained 16% of the variation in intelligence at each age.

CONCLUSIONS

Father's social class around the time of birth was an important predictor of childhood intelligence, even after adjustment for maternal characteristics and perinatal and childhood factors. Studies of the association of childhood intelligence with future adult disease need to ensure that the association is not fully explained by socioeconomic position.

Maternal body mass index, duration of exclusive breastfeeding and children's developmental status at the age of 6 years

OBJECTIVE

To investigate whether the duration of exclusive breastfeeding and maternal body mass index (BMI) are associated with children's developmental status at the time of beginning elementary school.

DESIGN AND SUBJECTS

The subjects in the sample came from a longitudinal study on infant nutrition in Iceland. Food records were made once a month from birth to the age of 12 months, from which duration of exclusive breastfeeding could be determined. Mothers filled in The Icelandic developmental inventory for evaluation of motor and verbal development close to their children's sixth birthday (n = 85). Maternal self-reported weight and height was recorded. Information on socioeconomic factors was gathered by a questionnaire.

RESULTS

Duration of exclusive breastfeeding, in months, was positively related to children's motor component (B = 0.5+/-0.5, P = 0.054) and to the total developmental index (B = 1.0+/-0.5, P = 0.044) at 6 y, adjusting for gender and socioeconomic factors (maternal and paternal education, and family income). Children's learning score was negatively related to maternal BMI (B = -0.5+/-0.2, P=0.047). An inverse association also appeared between maternal BMI and two out of the three developmental composite scores, that is, verbal component and the total developmental index (B = -0.6+/-0.3, P=0.049) and (B = -0.4+/-0.2, P=0.057), respectively. In multiple regression the developmental indexes were most strongly independently associated with maternal BMI (negatively) and infants' birth weight (positively).

CONCLUSION

Maternal BMI and duration of breastfeeding were associated with verbal and motor development of 6-y-old children, independent of socioeconomic factors. Birth weight was also an independent determinant for developmental scores.

Childhood cognitive ability and age at menopause: evidence from two cohort studies

OBJECTIVE

To investigate whether poorer cognitive ability in childhood is associated with an earlier menopause.

DESIGN

Two cohorts were included: a nationally representative British birth cohort study of 1,350 women born in March 1946 and followed up to age 54 years, and an Aberdeen cohort study of 3,465 women born in Aberdeen from 1950 to 1956 and followed up to age 44 to 50 years. Both cohorts had prospective information on childhood cognitive ability at age 7 or 8 years.

RESULTS

In both cohorts, women with lower cognitive scores in childhood reached menopause earlier than women with higher scores. With follow-up of menopause to 49 years, the hazard ratio (HR) for one standard deviation of the cognitive score was 0.80 (95% CI, 0.72-0.90) in the Aberdeen cohort and 0.84 (95% CI, 0.73-0.97) in the older 1946 birth cohort. The effect was still evident in the 1946 birth cohort with follow-up of menopause to 53 years (HR = 0.87; 95% CI, 0.79-0.95). These ratios were weakly attenuated by adjustment for potential confounding effects of lifetime socioeconomic circumstances, parity, and smoking.

CONCLUSIONS

The association between early cognitive ability and timing of menopause only partially reflects common risk factors, although residual confounding remains a possibility. Alternatively, early environmental or genetic programming may explain this association, perhaps through setting lifelong patterns of hormone release or causing transient hormonal changes at sensitive periods of development. These findings have implications for the interpretation of studies investigating an association between age at menopause and adult cognitive function.

Birth weight and psychological distress at age 45-51 years: results from the Aberdeen Children of the 1950s cohort study

BACKGROUND

It is unclear whether the effect of low birth weight on common affective disorders in later life is direct or mediated through childhood factors.

AIMS

To determine whether birth weight has a direct effect on psychological distress in adulthood not mediated by childhood IQ or behavioural problems.

METHOD

Participants (n=5572) of the Aberdeen Children of the 1950s study had data on birth weight for gestational age and adult psychological distress. Logistic regression was used to examine the association between these factors, with adjustment for confounders and potential childhood mediators.

RESULTS

Children born full term but weighing less than 5.5 lb had increased odds of psychological distress in later life after adjustment for potential confounders (OR=1.49, 95% CI 1.01-2.20). Further adjustment for childhood IQ and behaviour did not attenuate the association. A 1 s.d. decrease in birth weight for gestational age was associated with a 4% increased odds of psychological distress in adulthood (OR=1.04, 95% CI 0.97-1.12).

CONCLUSIONS

Low birth weight for gestational age, particularly at term, was associated with adult psychological distress. This was not mediated by childhood factors, suggesting a direct effect of early life factors on adult mental health. A neurodevelopmental pathway may therefore be implicated.

Seasonal fluctuations in birth weight and neonatal limb length; does prenatal vitamin D influence neonatal size and shape?

BACKGROUND

Birth weight is known to fluctuate with season of birth, however, there is little information about seasonal variation in neonatal anthropometric measures.

AIMS

The aim of this study was to examine seasonal fluctuations in birth weight and selected anthropometric measures.

STUDY DESIGN AND SUBJECTS

The birth weight of singletons born after at least 37 weeks gestation was extracted from a perinatal register in south-east Queensland (n=350,171). Mean monthly birth weights for this period were examined. Based on a separate birth cohort, principal component analysis was undertaken on neonatal anthropometric measures (n=1233). Seasonality was assessed by (a) spectral analysis of time series data, (b) monthly and seasonal comparison of outcomes.

RESULTS

Based on register data, birth weight displayed clear annual periodicity. Birth weight differed significantly when compared by month and season. Infants born in October were the heaviest (3484 g), while May-born infants were the lightest (3459 g; P=0.001). Based on the cohort anthropometric data, three components were identified related to (a) overall size, (b) limb length, and (c) head size and skin-fold thickness. Each of these components displayed significant seasonal variation. In particular, prominent seasonal fluctuations in limb length were identified, with peak limb length associated with winter/spring birth.

CONCLUSION

Environmental factors that have regular seasonal fluctuation influence both the size and shape of neonates. Animal experiments suggest that prenatal hypovitaminosis D may underlie greater limb length. Because birth weight and limb length are associated with a broad range of important health outcomes, the seasonal exposures underlying these effects warrant further scrutiny from a public health perspective.

Lung function and cognitive ability in a longitudinal birth cohort study

OBJECTIVE

The objective of this study was to examine the association between forced expiratory volume in 1 second (FEV1) and cognitive ability in midlife in the normal population.

METHODS

Multiple regression was used to test associations between FEV1 and cognitive function in 1778 men and women in the MRC National Survey of Health and Development, also known as the British 1946 birth cohort. Analyses were adjusted for sex, body size (birth weight, adult height, weight, and chest circumference), socioeconomic status, lifetime smoking, and a range of health indicators, including early respiratory vulnerability (infant lower respiratory infection, childhood asthma, and exposure to atmospheric pollution).

RESULTS

FEV1 at 43 years was associated with slower psychomotor speed (peg placement) at the same age and with slower decline in psychomotor speed (letter search speed) from 43 to 53 years, independently of the previously mentioned potential confounders. These independent associations were not observed, however, for adult verbal ability, verbal memory, or rate of decline in memory, which were significantly explained by socioeconomic status and adolescent cognitive ability. In a subsequent analysis, adolescent cognition was positively associated with FEV1, although not with rate of decline in FEV1 from 43 to 53 years, again independently of the previously mentioned confounders.

CONCLUSIONS

Cognitive function and FEV1 are positively associated across the life course. One possible explanation lies in the parallel action of endocrine, autonomic, and motor control systems on respiration and higher mental function. Because respiration and mental function are both associated with functional capacity and survival, this is a matter of potential clinical significance.

Effect of placental function on fatty acid requirements during pregnancy

The fetus has an absolute requirement for the n-3/n-6 fatty acids and docosahexaenoic acid (22:6 n-3; DHA) in particular is essential for the development of the brain and retina. Most of the fat deposition in the fetus occurs in the last 10 weeks of pregnancy. The likely rate of DHA utilisation during late pregnancy cannot be met from dietary sources alone in a significant proportion of mothers. De novo synthesis makes up some of the shortfall but the available evidence suggests that the maternal adipose tissue makes a significant contribution to placental transport to the fetus. The placenta plays a crucial role in mobilising the maternal adipose tissue and actively concentrating and channelling the important n-3/n-6 fatty acids to the fetus via multiple mechanisms including selective uptake by the syncytiotrophoblast, intracellular metabolic channelling, and selective export to the fetal circulation. These mechanisms protect the fetus against low long-chain polyunsaturated fatty acid (LCPUFA) intakes in the last trimester of pregnancy and have the effect of reducing the maternal dietary requirement for preformed DHA at this time. As a result of these adaptations, small changes in the composition of the habitual maternal diet before pregnancy are likely to be more effective in improving LCPUFA delivery to the fetus than large dietary changes in late pregnancy. There is little evidence that DHA intake/status in the second half of pregnancy affects visual and cognitive function in the offspring, but more studies are needed, particularly in children born to vegetarian and vegan and mothers who may have very low intakes of DHA.

Growth in early life and childhood IQ at age 11 years: the Newcastle Thousand Families Study

BACKGROUND

It has been suggested that in addition to genetic factors, fetal and post-natal growth influence childhood cognition, although it is unclear whether such an effect continues throughout childhood. This study aimed at investigating the potential relationships between childhood IQ at age 11 years and birth weight and height at the ages of 9 and 13 years, after adjusting for the confounding factors available to this investigation.

METHODS

The Newcastle Thousand Families study, a prospectively followed cohort, originally consisted of all 1142 births in the city of Newcastle in May and June 1947. Using data on 733 members of this cohort, we investigated the associations between IQ at age 11, and birth weight and height at ages 9 and 13 years.

RESULTS

Birth weight showed no association with childhood IQ. However, height at age 9 years was a significant predictor of childhood IQ after adjusting for socioeconomic status (standardized regression coefficient b = 2.6, 95% CI 1.6-3.6, P < 0.0001). Height at age 13 was also a significant predictor of IQ after adjusting for socioeconomic status (b = 3.4, 95% CI 2.3-4.4, P = 0.001), and explained an additional 2.5% of the variation in IQ scores to that already explained by socioeconomic status and height at age nine.

CONCLUSIONS

These results suggest a continuing effect of post-natal growth on childhood cognition beyond the age of 9 years. Post-natal growth, which may be influenced by genetic factors and nutrition and socioeconomic circumstances in childhood, may be more important than fetal growth in terms of childhood cognition.

A review of low birth weight: predictors, precursors and morbidity outcomes

This paper reviews the global evidence concerning infant low birth weight (LBW) (2.500kg and below) in relation to suggested causative factors, such as undernutrition, stress, smoking, drug abuse and deprived living environments. In addition, health promotion strategies in place to reduce LBW incidence in both developed and underdeveloped countries are reviewed. The paper also focuses on the high incidence of LBW in the UK in comparison to other European and developed countries. Predictors of LBW are then considered comparing findings of a study conducted in the UK with findings in underdeveloped countries. In addition, LBW risk is discussed in the context of vulnerability factors, such as teen pregnancy, child abuse and domestic violence. In conclusion, the author argues for a health promotion policy in the UK to reduce incidence of LBW in areas of deprivation and suggests that the improvement of maternal health is key in improving the health of today's infants and children who will one day become the adults of tomorrow.

Birth weight and cognitive ability in childhood: a systematic review

Individual differences in cognitive ability may in part have prenatal origins. In high-risk (low birth weight/premature) babies, birth weight correlates positively with cognitive test scores in childhood, but it is unclear whether this holds for those with birth weights in the normal range. The authors systematically reviewed literature on the relationship between normal birth weight (more than 2,500 g) and childhood intelligence in term (37-42-week gestation) deliveries. Six studies met the inclusion criteria, and the authors present a comprehensive narrative review of these studies. There was a small, consistent, positive association between birth weight and childhood cognitive ability, even when corrected for confounders. Parental social class accounted for a larger proportion of the variance than birth weight, and these 2 variables were largely independent.

Cognitive performance in childhood and early adult illness: a prospective cohort study

STUDY OBJECTIVE

To evaluate whether cognitive performance in childhood is an early determinant of adult illness.

DESIGN

Prospective cohort study covering over 30 years.

SETTING

Providence, Rhode Island, USA.

PARTICIPANTS

633 people ages 30-39 followed up since birth as part of the Providence cohort of the national collaborative perinatal project.

MAIN RESULTS

Higher cognitive performance at age 7 was related to a significantly reduced risk of serious illness in adulthood, OR = 0.65 (95%CI: 0.47 to 0.89) for a one standard deviation (15 point) increase in IQ score. This association was independent of both parental socioeconomic status and participant's attained level of education.

CONCLUSIONS

General cognitive performance may be an important and informative early determinant of adult health. Further evaluation of this association and mechanisms linking cognitive performance and health may provide new and innovative strategies to improve disease management and reduce morbidity.