The association of high birth weight with intelligence in young adulthood: a cohort study of male siblings

Birth size, school performance and family social position: a study of 650,000 children

BACKGROUND

Low birth weight (BW) is associated with lower cognitive functioning, but less is known of these associations across the full range of the BW distribution and its components. We analyzed how BW, birth length (BL) and birth ponderal index (BPI, kg/m3) are associated with school performance and how childhood family social position modifies these associations.

METHODS

Medical birth records of all Finnish children born in 1987-1997 were linked to school performance records at 16 years of age (N = 642,425). We used population averaged and within-siblings fixed-effects linear regression models.

RESULTS

BL showed a linear and BW a curvilinear association with school performance whereas for BPI the association was weak. The strongest association was found for BL explaining 0.08% of the variation in school performance in boys and 0.14% in girls. Demographic, gestational and social factors partly explained these associations. Similar but weaker associations were found within sibships. The association of BL with school performance was stronger at lower levels of family social position.

CONCLUSION

BL shows a linear association with school performance and can explain more school performance variation than BW. At the population level, BL can offer useful information on intrauterine environmental factors relevant for cognitive performance.

IMPACT

Birth length is linearly associated with school performance in late adolescence and explains a larger proportion of school performance variation than birth weight. The association between birth length and school performance is stronger in families with lower socio-economic position. At the population level, birth length can offer information on the intrauterine environment relevant for later cognitive performance.

[Effects of High Birth Weight on the Development of Preschoolers]

BACKGROUND

A high birth weight above 4,000 g may lead to risks in the development of affected children. The association is less studied than the effects of very low birth weight and is the subject of this study.

METHODS

The retrospective study design used data from school entry surveys in Schleswig-Holstein (Germany) collected in 2014-2017 and included 88,858 children aged 5-6 years. End points examined were language, motor skills, cognition, and behavior; use of support measures; and recommendation for special educational needs. Logistic regression models were used to estimate the association between birth weight and the outcome measures, adjusting for sociodemographic factors.

RESULTS

After accounting for sociodemographic factors, high birth weight is not associated with impaired child development, whereas low birth weight emerges as a significant predictor. Across all birth weights, sociodemographic factors explain most of the variance in multivariate models of the influence of birth weight on child development.

CONCLUSIONS

Very high birth weight does not justify a general recommendation for support measures. Therefore, individual developmental trajectories should be monitored. Growing up in disadvantaged circumstances may represent a significant risk and should be a reason for early intervention.

Birth weight and adult earnings: a systematic review and meta-analysis

While substantial evidence has identified low birth weight (LBW; <2500 g) as a risk factor for early life morbidity, mortality and poor childhood development, relatively little is known on the links between birth weight and economic outcomes in adulthood. The objective of this study was to systematically review the economics (EconLit) and biomedical literature (Medline) and estimate the pooled association between birth weight and adult earnings. A total of 15 studies from mostly high-income countries were included. On average, each standard deviation increase in birth weight was associated with a 2.75% increase in annual earnings [(95% CI: 1.44 to 4.07); 9 estimates]. A negative, but not statistically significant, association was found between being born LBW and earnings, compared to individuals not born LBW [mean difference: -3.41% (95% CI: -7.55 to 0.73); 7 estimates]. No studies from low-income countries were identified and all studies were observational. Overall, birth weight was consistently associated with adult earnings, and therefore, interventions that improve birth weight may provide beneficial effects on adult economic outcomes.

Mendelian randomization suggests that head circumference, but not birth weight and length, associates with intelligence

INTRODUCTION

Birth parameters have long been reported to have a role in human intelligence. However, the causalities reported in previous observational studies were controversial. Our study aims to provide an unbiased investigation of the causal associations between birth parameters and human intelligence using the Mendelian randomization (MR) approach.

METHODS

Genetic instrumental variables for MR analyses were extracted from large genome-wide association studies of infant head circumference (N = 10,768), birth length (N = 28,489), and birth weight (N = 321,223). Data for intelligence were obtained from a meta-analysis of genome-wide association studies of 269,867 individuals of the European ancestry. Primary MR analysis was performed using the standard inverse-variance weighted method, and sensitivity analyses were performed using the weighted median, MR-Egger, and MR-PRESSO methods.

RESULTS

Using 10 single nucleotide polymorphisms as instrumental variables, we found that 1 standard deviation increase in infant head circumference was associated with 0.14-fold higher scores in intelligence tests (β = 0.14, 95% confidence interval: 0.09 to 0.18, P_IVW =2.05 × 10^-9 ). The causal relationship was robust when sensitivity analyses were performed. However, birth length and birth weight had no significant associations with intelligence.

CONCLUSION

Our findings suggested infant head circumference, but not birth weight and length were associated with intelligence, which might indicate that brain development rather than general fetal growth was responsible for the development of intelligence.

The Association Between High Birth Weight and Long-Term Outcomes-Implications for Assisted Reproductive Technologies: A Systematic Review and Meta-Analysis

Background: Studies have shown that the prevalence of children born with high birth weight or large for gestational age (LGA) is increasing. This is true for spontaneous pregnancies; however, children born after frozen embryo transfer (FET) as part of assisted reproductive technology (ART) also have an elevated risk. In recent years, the practice of FET has increased rapidly and while the perinatal and obstetric risks are well-studied, less is known about the long-term health consequences. Objective: The aim of this systematic review was to describe the association between high birth weight and LGA on long-term child outcomes. Data Sources: PubMed, Scopus, and Web of Science were searched up to January 2021. Exposure included high birth weight and LGA. Long-term outcome variables included malignancies, psychiatric disorders, cardiovascular disease, and diabetes. Study Selection: Original studies published in English or Scandinavian languages were included. Studies with a control group were included while studies published as abstracts and case reports were excluded. Data Extraction: The methodological quality, in terms of risk of bias, was assessed by pairs of reviewers. Robins-I (www.methods.cochrane.org) was used for risk of bias assessment in original articles. For systematic reviews, AMSTAR (www.amstar.ca) was used. For certainty of evidence, we used the GRADE system. The systematic review followed PRISMA guidelines. When possible, meta-analyses were performed. Results: The search included 11,767 articles out of which 173 met the inclusion criteria and were included in the qualitative analysis, while 63 were included in quantitative synthesis (meta-analyses). High birth weight and/or LGA was associated with low to moderately elevated risks for certain malignancies in childhood, breast cancer, several psychiatric disorders, hypertension in childhood, and type 1 and 2 diabetes. Conclusions: Although the increased risks for adverse outcome in offspring associated with high birth weight and LGA represent serious health effects in childhood and in adulthood, the size of these effects seems moderate. The identified risk association should, however, be taken into account in decisions concerning fresh and frozen ART cycles and is of general importance in view of the increasing prevalence in high birthweight babies.

The Norwegian Armed Forces Health Registry conscription board health examinations 1968-2018

Aim: The aim of the study is to encourage further research initiatives and collaborations based on Norwegian Armed Forces Health Registry (NAFHR) data by presenting basic information on the data contained therein. Methods: We describe how conscription board health examinations (CBHEs) are carried out, how results are recorded in the NAFHR, and the completeness of NAFHR data that are electronically available for research purposes. Results: In December 2018, the NAFHR contained data on nearly 1.5 million Norwegian citizens (95% men) who attended CBHE in 1968-2018 at the age of 17-19 years. The percentage of persons included from each birth cohort has varied as the Armed Forces' personnel requirements and filing procedures have changed, increasing from 73% of eligible men born in 1950 to 95% of eligible men born in 1960-1991. In 2010 a preselection of candidates was implemented wherefore less than half of men born in 1992-2000 are registered in the NAFHR. Information on aerobic fitness, cognitive general ability, height and weight is registered for approximately 95% of individuals included in the NAFHR. The NAFHR contains more detailed health information for CBHEs that took place as from 1980, and information included from 2011 onwards is the most detailed. Unique, national personal identification numbers may be used to link the NAFHR to other health registries or data sources for public health research. Conclusions: The NAFHR contains CBHE data on the majority of Norwegian men and a substantial number of women born since 1950. NAFHR data represent a valuable resource for research collaborations.

Differences and secular trends in childhood IQ trajectories in Guatemala City

This study documents differences in childhood IQ trajectories of Guatemala City children, aged 6-15 years and born 1961-1993, according to school attended, height-for-age Z-scores (HAZ) and over time (Flynn effect). IQ data come from the Universidad del Valle de Guatemala Longitudinal Study of Child and Adolescent Development. IQ was measured using standardised tests from the Otis-Lennon Mental Ability Test-series. A multilevel model was developed to describe 60,986 IQ observations (level 1), in 22,724 children (level 2), in five schools representing students of different socioeconomic status (SES) (level 3). Average IQ trajectories differed by school. The difference in average IQ at age 11 years between the students of high and low SES schools was 28.7 points. A one-unit increase in HAZ was associated with a 1.42 (0.72, 2.11) unit higher IQ if HAZ was <0, this association was stronger in public compared to private schools. Conversely, one unit increase in HAZ was only associated with a 0.3 (0.001, 0.5) unit higher IQ if HAZ was ≥0. With each birth year increase, IQ at age 11 years increased by 0.14 (95% CI 0.12, 0.16) units, although this Flynn effect attenuated slightly across adolescence. We found no evidence of secular change in the inequality in IQ trajectories (according to school or HAZ). Shorter children from disadvantaged schools in Guatemala City have lower IQ than their taller and wealthier peers, possibly reflecting the damaging effects of poor early life environments both for linear growth and cognitive development.

Mechanism associated with aberrant lncRNA MEG3 expression in gestational diabetes mellitus

Gestational diabetes mellitus (GDM) is a common metabolic condition during pregnancy. Long non-coding RNAs (lncRNAs) have been found to seve critical roles in GDM development; however, the role of lncRNA maternally expressed gene 3 (MEG3) in GDM remains unclear. Therefore, the aim of the present study was to investigate the expression and role of MEG3 in GDM, and to further explore the underlying mechanism. The levels of lncRNA MEG3 in the blood and placental villous tissues of pregnant women with GDM was measured using reverse transcription-quantitative PCR. Bioinformatics analysis and dual luciferase reporter assays were performed to investigate the association between lncRNA MEG3 and microRNA (miR)-345-3p. Transfection was subsequently performed on HTR-8/SVneo cells, a human chorionic trophoblast cell line, to assess the role of lncRNA MEG3 in GDM. In particular, cell viability, cellular migratory/invasive ability and cell apoptosis were analyzed using MTT assay, Transwell assay and flow cytometry, respectively. Compared with pregnant women without GDM, lncRNA MEG3 levels were significantly elevated in the blood and placental villous tissues of GDM pregnant women. miR-345-3p was identified to be a direct target of lncRNA MEG3 using dual luciferase reporter assay, which was found to be reduced in pregnant women with GDM. Further analysis demonstrated that lncRNA MEG3 overexpression significantly inhibited HTR-8/SVneo cell viability, and prevented cell migration and invasion in addition to inducing cell apoptosis. In contrast, lncRNA MEG3 knockdown significantly enhanced HTR-8/SVneo cell viability, promoted cell migration/invasion and reduced cell apoptosis. Inhibiting miR-345-3p expression negated all the observed physiological effects of lncRNA MEG3 knockdown on HTR-8/SVneo cells. In conclusion, lncRNA MEG3 levels were abnormally upregulated in GDM, which participated in the development and progression of GDM by regulating human chorionic trophoblast cell physiology. Therefore, lncRNA MEG3 may be a potential diagnostic and therapeutic target for GDM.

Risk factors for recurrent macrosomia and child outcomes

BACKGROUND

Women who had delivered a macrosomic newborn will have a higher risk to deliver another macrosomia. We aimed to examine the recurrence risk of macrosomia in the subsequent pregnancy and the implications in long-term child health.

METHODS

Data from the Collaborative Perinatal Project, a longitudinal birth cohort with 54,371 singleton births, were used. 401 recurrent macrosomic infants (macro-macro) and 1327 normal weight babies with a macrosomia in the last pregnancy (macro-normal) were selected to explore risk factors for recurrent macrosomia. Furthermore, 768 newly onset macrosomia with normal birthweight infant in previous pregnancies (normal-macro) were identified to examine long-term health effects of recurrent macrosomia.

RESULTS

The recurrent rate of macrosomia was 23.2% [95% confidence interval (CI) 21.2%, 25.2%]. White race, higher pre-pregnant body mass index (BMI), more gestational weight gain, male infant and more prior macrosomic infants were significant risk factors for recurrent macrosomia. At 4 years of age, recurrent macrosomic infants had a higher BMI (16.7 vs. 16.1 kg/m², adjusted β: 0.36, 95% CI: 0.12, 0.60) and a higher risk of overweight and obesity (adjusted OR: 1.56, 95% CI: 1.10, 2.23) than infants with normal birthweight after a previous macrosomic sibling. There was no significant difference between recurrent macrosomia and newly onset macrosomia in child outcomes after adjustment for covariates.

CONCLUSIONS

Fetal macrosomia has a high recurrence rate in the following pregnancy. Higher maternal pre-pregnant BMI and gestational weight gain are still important risk factors for recurrence of macrosomia, which in turn increases the risk for childhood obesity.

What birthweight percentile is associated with optimal perinatal mortality and childhood education outcomes?

BACKGROUND

Small for gestational age, defined as birthweight <10th percentile for gestational age, is known to be associated with clinically meaningful impairments in health and development. The effects of variation within the normal range of birthweight percentile on perinatal mortality and childhood education remain less well defined.

OBJECTIVE

We sought to quantify the association among birthweight percentile, perinatal mortality, and educational outcomes and to determine the optimal birthweight percentile for those outcomes in Aboriginal and non-Aboriginal Australian children.

STUDY DESIGN

This was a retrospective cohort study. Perinatal data for all children born in the Northern Territory, Australia, from 1999 through 2008 were linked to measures of educational attainment at age 8-9 years. Multivariable analysis was used to determine the optimal birthweight percentile for low perinatal mortality and high reading and numeracy scores.

RESULTS

The birth cohort contained 35,239 births (42% Aboriginal), of which 11,214 had linked and valid education records. Median birthweight percentile was 29.2 in Aboriginal infants and 44.0 in non-Aboriginal infants. The odds of perinatal mortality decreased by 4% with each 1-percentile increase birthweight percentile overall (adjusted odds ratio, 0.96; P = .000) and lowest mortality rates were at the 61st and 78th percentile in Aboriginal and non-Aboriginal infants, respectively. Although birthweights <10th percentile were associated with greatly increased odds of perinatal mortality, the increased risk extended well beyond this cut-off. Birthweight percentile was also positively correlated with scores in reading (P = .000) and numeracy (P = .000). In non-Aboriginal children, reading and numeracy scores peaked at the 66th percentile, but for Aboriginal children there was continuous benefit with increasing birthweight percentile. Birthweight percentile explained 1% of the variation in education outcomes, with much greater variation explained by other perinatal and sociodemographic factors.

CONCLUSION

Birthweights between the 50th-93rd percentiles were most consistently associated with both low perinatal mortality and high reading and numeracy scores, suggesting that small for gestational age does not sufficiently capture the risks associated with variation in fetal growth. Our data indicate that the effect of birthweight percentile accounts for 1% of variation in perinatal and education outcomes.

High birth weight and perinatal mortality among siblings: A register based study in Norway, 1967-2011

BACKGROUND

Perinatal mortality according to birth weight has an inverse J-pattern. Our aim was to estimate the influence of familial factors on this pattern, applying a cohort sibling design. We focused on excess mortality among macrosomic infants (>2 SD above the mean) and hypothesized that the birth weight-mortality association could be explained by confounding shared family factors. We also estimated how the participant's deviation from mean sibling birth weight influenced the association.

METHODS AND FINDINGS

We included 1 925 929 singletons, born term or post-term to mothers with more than one delivery 1967-2011 registered in the Medical Birth Registry of Norway. We examined z-score birth weight and perinatal mortality in random-effects and sibling fixed-effects logistic regression models including measured confounders (e.g. maternal diabetes) as well as unmeasured shared family confounders (through fixed effects models). Birth weight-specific mortality showed an inverse J-pattern, being lowest (2.0 per 1000) at reference weight (z-score +1 to +2) and increasing for higher weights. Mortality in the highest weight category was 15-fold higher than reference. This pattern changed little in multivariable models. Deviance from mean sibling birth weight modified the mortality pattern across the birth weight spectrum: small and medium-sized infants had increased mortality when being smaller than their siblings, and large-sized infants had an increased risk when outweighing their siblings. Maternal diabetes and birth weight acted in a synergistic fashion with mortality among macrosomic infants in diabetic pregnancies in excess of what would be expected for additive effects.

CONCLUSIONS

The inverse J-pattern between birth weight and mortality is not explained by measured confounders or unmeasured shared family factors. Infants are at particularly high mortality risk when their birth weight deviates substantially from their siblings. Sensitivity analysis suggests that characteristics related to maternal diabetes could be important in explaining the increased mortality among macrosomic infants.

Invited commentary: Interpreting associations between high birth weight and later health problems

High birth weight (>4.0 kg) has been associated with a wide range of health problems later in life. The interpretation of these statistical associations may be difficult, however. These difficulties are closely linked to methodological challenges in this research, such as filtering out confounding from family factors, disentangling associations with prenatal processes from associations with postnatal processes, and uncovering what birth weight actually represents. The well-conducted study by Kristensen et al. (Am J Epidemiol. 2014;180(9):876-884), presented in this issue of the Journal, offers an interesting example of how one can filter out confounding from family factors. In an elegant series of analyses, the authors show how an apparent inverse association between birth weight and later intelligence among those in the highest range of the birth weight scale became a positive association when proper adjustment for family factors was made. Sibling comparisons were important here.