External Publications Using GUI Data

A large body of international literature has documented a correlation between nontraditional family structure and poorer child outcomes, yet researchers continue to disagree as to whether the association represents a true causal effect. This article extends this literature by employing propensity score matching using the first wave of data from the Growing up in Ireland child cohort study. We argue that the Irish case is of particular interest given the highly selective nature of non-marriage. We find that, on average, non-marriage has negative effects on a child educational development at age 9 but the effects are smaller in relation to health outcomes and the child’s self-concept. However, selection effects account for a non-trivial proportion of the differences in child outcomes across lone-mother and cohabiting families although hidden bias remains an important issue. This has important implications for policies which promote marriage as the key to child development as it appears that much of the benefits of marriage are not related to marriage per se but to the socio-economic background of mothers.

The purpose of this report is to investigate the known correlation between non-traditional family structures and poor outcomes for children.

Discussions of this topic often focus on the distinction between two-parent families and one-parent families but this distinction can be misleading. In the Irish case, the crucial distinction is between children raised by parents who are married and children raised by a lone-parent who has never been married. The focal point here is non-marriage.

This is important since non-marriage appears to be highly selective because the least privileged groups in Irish society are more likely to have children outside of marriage and at a relatively early age.

This argument suggests that selection bias accounts for much of the association between family structure and child outcome i.e. growing up in a non-traditional family has little ‘direct’ or ‘causal’ effect on a child’s outcome. A large body of literature exists which documents a correlation between non-traditional family structure and poorer child development but researchers disagree as to whether this association represents a true causal effect.

The primary objective of the current study, therefore, is to test this selection argument and to examine the extent to which selection effects can account for differences in child wellbeing in various family types.

Psychotic experiences (PEs) are common in early adolescence and are associated with nonpsychotic psychopathology. However, not all adolescents with PEs have subsequent psychopathology, and vice versa. To date, factors mediating the relationship between PEs and psychopathology have been understudied. The aims of this study were to investigate the bidirectional relationship between PEs and psychopathology in adolescence and to investigate potentially malleable mediators of these relationships. Data from 2 waves (age 13 and 17 years) of Cohort ’98 of the Growing Up in Ireland study were examined (n = 6,206). Using KHB pathway decomposition, we investigated the following as potential mediators of the relationship between psychopathology and PEs: parent-child relationship (conflict and positive), self-concept, and child-peer relationship (alienation and trust). Supplementary counterfactual mediation and sensitivity analyses were conducted. Early adolescents with psychopathology had twofold increased odds of late adolescent PEs (internalizing problems: odds ratio [OR] = 2.03, 95% confidence interval [CI; 1.56, 2.62]; externalizing problems: OR = 1.99, CI [1.51, 2.60]). Parent-child conflict explained between 23% and 34% of the associations between internalizing and externalizing problems and subsequent PEs. Early adolescents with PEs had increased odds of late adolescent psychopathology (internalizing problems: OR = 2.01, CI [1.61, 2.50]; externalizing problems: OR = 1.70, CI [1.25, 2.31]). Self-concept alone accounted for 52% of the relationship between PEs and subsequent internalizing problems. There is a bidirectional heterotypic relationship between psychopathology and PEs. Parent-child conflict and self-concept are important characteristics that mediate a proportion of the relationship between PEs and psychopathology. Interventions targeting parent-child conflict in the context of psychopathology and self-concept in the context of PEs may assist in reducing the incidence of poorer outcomes.

Background
Psychotic experiences (PEs) are commonly reported in adolescence and are associated with a range of negative outcomes. Few targets for intervention for PEs have been identified. One potential target is self-concept: an individual’s beliefs about his/her personal attributes. Improvements in self-concept have been shown to reduce psychotic symptoms in patients with schizophrenia but no study has investigated the relationship between changes in self-concept and risk of PEs in the general population.

We aimed to investigate: (a) the relationship between child and adolescent self-concept and adolescent PEs; and (b) whether changes in self-concept between childhood and adolescence were associated with risk of adolescent PEs.

Method
Using data from age 9 and age 13 (n = 7,423) of the child cohort (Cohort’98) from the Growing Up in Ireland study we investigated the relationship between self-concept at age 9 and age 13 and PEs at age 13. PEs were measured using the Adolescent Psychotic Symptoms Screener and self-concept was measured using the Piers Harris-II. Using a stratified analysis, we investigated the relationship between change in self-concept between age 9 and age 13 and the risk of PEs at age 13. Additionally we investigated changes across the six self-concept subscales.

Results
Psychotic experiences were reported by 13% of participants at age 13. ‘Very low’ self-concept at age 9 was associated with an increased risk of PEs at age 13 (Adjusted-OR: 2.74, CI: 1.80–4.19), and ‘High’ self-concept at age 9 was associated with a decreased risk of PEs at age 13 (Adjusted-OR: 0.77, CI: 0.60–0.97). The stratified analysis indicated that improvements in self-concept reduced the odds of adolescent PEs and decline in self-concept increased the odds of adolescent PEs. This effect was noted across the majority of the self-concept subscales.

Conclusions
There is a strong relationship between self-concept and PEs. The antecedents of low self-concept may be a useful target for preventative psychiatry. Broad-spectrum interventions targeting self-concept in childhood may help to reduce the incidence of PEs in adolescence

Background
Childhood adversity (CA) is commonly associated with an increased risk of subsequent psychopathology. It is important to identify potential mediators of this relationship which can allow for the development of interventions. In a large population-based cohort study we investigated the relationship between CA and late adolescent psychopathology and early adolescent candidate mediators of this relationship.

Methods
We used data from three waves (n = 6039) of Cohort 98′ of the Growing up in Ireland Study (age 9, 13 and 17). We used doubly robust counterfactual analyses to investigate the relationship between CA (reported at age-9) with psychopathology (internalizing and externalizing problems), measured using the Strengths and Difficulties Questionnaire at age-17. Counterfactual and traditional mediation was used to investigate the mediating effects of the parent-child relationship, peer relations, self-concept, computer usage and physical activity.

Results
CA was associated with an increased risk of internalizing and externalizing problems at age-17. Parent-child conflict mediated 35 and 42% of the relationship between CA and late adolescent externalizing problems and internalizing problems, respectively. Self-concept and physical activity mediated an additional proportion of the relationship between CA and internalizing problems. These results were robust to unmeasured confounding.

Conclusions
Parent-child conflict explains more than a third of the relationship between CA and later psychopathology. Self-concept and physical activity explain the additional proportion of the relationship between CA and internalizing problems. This suggests that these factors may be good targets for intervention in young people who have experienced CA to prevent subsequent psychopathology.

Keywords
Childhood adversity, parent-child conflict, psychopathology, self-concept and physical activity

In an effort to promote optimal health in all children, 24-hour movement guidelines that provide specific recommendations for physical activity, screen-time, and sleep have been developed (≥ 1 hour of physical activity, ≤ 2 hours of screen-time, 9-11 hours of sleep). Children who meet the recommendations for these health behaviours are less likely to be obese than those who do not meet them. This study compared the degree to which children with autism spectrum disorder (ASD) and typically developing (TD) children met the newly developed 24-hour movement guidelines. A propensity-score matched sample of 72 children (36 children with ASD, 36 TD children) from the “Growing Up in Ireland” study was included in the analysis. Based on parents’ completion of time-use diaries, fewer children with ASD, compared to TD children, met the recommendations for screentime (58.3% vs. 80.6%, p=0.07, V=0.24) and physical activity (41.7% vs. 69.4%, p=0.03, V=0.28). Children with ASD were most likely to meet two guidelines (44.4%), whereas TD children most commonly met all three guidelines (55.6%). The findings highlight the breadth of health behaviours that require intervention among children with ASD. The current study suggests that examining the movement behaviours that constitute a 24-hour period for children with ASD may be useful to inform interventions to reduce their risk for sub-optimal health.

Keywords: Physical activity; Screen-time; Sleep; Autistic; exercise; sedentary behaviour; health; overweight; obesity

The prevalence of obesity in children is rapidly rising, leading to many serious consequences worldwide. In 2005, the World Health Organisation (WHO) Regional Office for Europe issued recommendations and guidelines for regular collection of data on weight, height, and waist and hip circumference in children worldwide in order to monitor prevalence trends of growth, overweight and obesity. The Department of Health and the Health Service Executive commissioned the National Nutrition Surveillance Centre, based at the School of Public Health, Physiotherapy and Population Science in University College Dublin, to carry out this surveillance work in the Republic of Ireland.

This report presents the findings from three waves of the WHO Childhood Obesity Surveillance Initiative survey in the Republic of Ireland in 2008, 2010 and 2012. In 2008, 163 randomly selected primary schools participated in this project and in the first round the protocol as set out by the WHO for participating countries was followed. The target age was children aged exactly 7 years. In the subsequent two waves, the same WHO protocol was followed and the same schools were contacted again and this time, as well as 7-year-olds, 9-year-olds were also selected for participation in the second round. In the third round, 7-year, 9-year, as well as 11-year-olds were included.

This means that there are three cross-sectional surveys of 7-year-old children, two cross-sectional surveys of 9-year-olds and one cross-sectional comparison group of 7-, 9- and 11-year-old children. Using a unique identifier there are also two cohort groups of the same children followed on two separate occasions from ages 7 to 9 and ages 9 to 11, respectively. In this report, we also compare the data on 9-year-old children to the findings from the Growing Up in Ireland Cohort study.

The aim of this study was to examine the role of different types of home learning activities, such as reading, singing, painting, playing games, and letters and numbers (ABCs and 123 s), in the development of nonverbal reasoning skills in young children. Although much previous research has focused on the role of the home learning environment in the development of language and numeracy skills, few studies have explored other aspects of cognitive development such as nonverbal reasoning. The data were drawn from the Growing Up in Ireland study, a nationally representative longitudinal birth cohort study. We examined whether learning activities were associated with scores on standardized nonverbal reasoning and vocabulary tests of the British Ability Scales in a sample of 9793 3-year-old children. The regression models also controlled for other factors that potentially influence cognitive development such as the parent–child relationship and maternal education. The findings indicate that activities such as reading, games, and painting/drawing have a small but statistically significant association with nonverbal reasoning scores, as well as with vocabulary scores, even after controlling for other factors in the model. Teaching the alphabet or numbers did not make significant contributions to the model. The findings of the study highlight the importance of considering the role of different types of home learning activities, as well as other environmental factors, in different aspects of cognitive development. We consider the implications of the findings for theories of cognitive development and for supporting cognitive development in young children.

The aim of this study was to identify, using cluster analysis, novel sleep phenotypes in a population based cohort of infants, and to explore the associations between infant sleep profiles and their mothers’ health and well-being. 11,134 mothers of 9-month old infants were interviewed as part of the Growing Up in Ireland National Longitudinal study and reported on their health and infant’s sleep patterns. 16 infant sleep variables were recorded together with measures of parental stress, depression, health and well-being. Multiple iterations of a two-step hierarchical cluster analysis were carried out to identify the optimum number of clusters and the subset of parental-reported sleep variables required to identify distinct sleep profiles. Four distinct sleep profiles were identified based on the following variables; (1) infant sleep duration at night, (2) parental sleep duration, (3) does baby wake during night (yes, no)? (4) Usual sleep location for most of the night and, (5) parental reporting of problem infant sleep patterns. This identified two less favorable profiles with both infants and mothers sleeping less and where mothers are more likely to report their infants’ sleep patterns as problematic. Mothers of infants belonging to these sleep profiles were more likely to have higher levels of stress, depressive symptoms, and poorer self-reported health than other sleep profiles. Breastfeeding was associated with both groups and rates were highest in a group of infants that were more likely to co-sleep with their parents and have diverse ethnic backgrounds. This study demonstrates, for the first time, two infant sleep profiles with distinct phenotypical frameworks that are significantly associated with maternal stress, depression, and poorer self-report of health.

Objective
To longitudinally investigate body mass index (BMI) in young children in Ireland and identify factors and critical time points associated with changes in BMI.

Study design
Data on 11 134 children were collected in the nationally representative Growing Up in Ireland infant cohort study. Height and weight were measured at 9 months, 3 years, and 5 years of age. Multilevel regression was used to identify risk factors associated with changes in BMI over time (n = 10 377), combining a unique set of covariates collected from the child and the 2 main caregivers (usually the mother and father).

Results
The proportion of children ≥85th percentile of World Health Organization growth criteria was 39% at 9 months, 44% at 3 years, and 30% at 5 years. Children born large for gestational age (13%) and those with rapid infant weight gain (25%) consistently had higher BMI. Low average BMIs were consistently seen in children born small for gestational age (10%) or before 37 weeks (7%). Smaller variations in BMI existed for other factors including ethnicity, household structure, caregiver weight status, breastfeeding, sex, socioeconomic status, sleeping hours, childcare, and region.

Conclusions
In this study, differences at birth and in infancy appear to be most strongly associated with variation in BMI at all ages. Nevertheless, belonging to a number of other high-risk groups cumulatively could lead children to develop critical weight states. Policy-makers should target families with interventions before and during pregnancy when dominant risk factors are still modifiable. Longer-term follow-up of children may be needed to study associations later in childhood.

Keywords
Growing Up in Ireland, body mass index, childhood obesity, growth trajectories, multilevel modelling

Aims
Multiple studies have connected parenting styles to children’s internalising and externalising mental health symptoms (MHS). However, it is not clear how different parenting styles are jointly influencing the development of children’s MHS over the course of childhood. Hence, the differential effects of parenting style on population heterogeneity in the joint developmental trajectories of children’s internalising and externalising MHS were examined.

Method
A community sample of 7507 young children (ages 3, 5 and 9) from the Growing Up in Ireland cohort study was derived for further analyses. Parallel-process linear growth curve and latent growth mixture modelling were deployed.

Results
The results indicated that the linear growth model was a good approximation of children’s MHS development (CFI = 0.99, RMSEA = 0.03). The growth mixture modelling revealed three classes of joint internalising and externalising MHS trajectories (VLMR = 92.51, p < 0.01; LMR = 682.19, p < 0.01; E = 0.86). The majority of the children (83.49%) belonged to a low-risk class best described by a decreasing trajectory of externalising symptoms and a flat low trajectory of internalising MHS. In total, 10.07% of the children belonged to a high-risk class described by high internalising and externalising MHS trajectories, whereas 6.43% of the children were probable members of a mild-risk class with slightly improving yet still elevated trajectories of MHS. Adjusting for socio-demographics, child and parental health, multinomial logistic regressions indicated that hostile parenting was a risk factor for membership in the high-risk (OR = 1.47, 95% CI 1.18–1.85) and mild-risk (OR = 1.57, 95% CI 1.21–2.04) classes. Consistent (OR = 0.75, 95% CI 0.62–0.90) parenting style was a protective factor only against membership in the mild-risk class.

Conclusions
In short, the findings suggest that a non-negligible proportion of the child population is susceptible to being at high risk for developing MHS. Moreover, a smaller proportion of children was improving but still displayed high symptoms of MHS (mild-risk). Furthermore, hostile parenting style is a substantial risk factor for increments in child MHS, whereas consistent parenting can serve as a protective factor in cases of mild-risk. Evidence-based parent training/management programmes may be needed to reduce the risk of developing MHS.

Background
Past empirical evidence on the longitudinal relations between emotional mental health symptoms and parent-child close relationships has produced mixed and inconclusive results. Some studies suggest a unidirectional relation, whereas other studies point toward a bidirectional association. Additionally, most of the past research has been carried out with adolescent samples, rather than children. Hence, this study aimed to estimate the longitudinal relations between children’s trait emotional difficulties and trait parent-child closeness, accounting for the time-invariant and time-varying state components of each factor.

Methods
Participants were 7,507 children (ages 3 years, 5 years, 7 years, and 9 years) from the Growing Up in Ireland cohort. Α bivariate stable trait, autoregressive trait, and state (STARTS) model was estimated using Bayesian structural equation modelling.

Results
The STARTS model revealed that children’s emotional difficulties and parent-child closeness were relatively stable across time, and these overarching traits were strongly negatively correlated. Children’s earlier trait emotional difficulties predicted later trait parent-child closeness and vice versa between 3 years and 5 years, and between 5 years and 7 years, but these effects disappeared between 7 years and 9 years. At all pairs of time points, state emotional difficulties and state parent-child closeness were weakly negatively correlated.

Conclusions
Overall, the results suggest that early and middle childhood are critical stages for improving parent-child relationships and reducing children’s emotional difficulties. Developing close parent-child relationships in childhood appears to be a key factor in reducing children’s subsequent emotional difficulties. Children who face greater than usual emotional difficulties tend to be more withdrawn and less receptive to close parent-child relationships and this could serve as an important screening indicator.

Background
Parental obesity is a predominant risk factor for childhood obesity. Family factors including socio-economic status (SES) play a role in determining parent weight. It is essential to unpick how shared family factors impact on child weight. This study aims to investigate the association between measured parent weight status, familial socio-economic factors and the risk of childhood obesity at age 9.

Methodology/Principal Findings
Cross sectional analysis of the first wave (2008) of the Growing Up in Ireland (GUI) study. GUI is a nationally representative study of 9-year-old children (N = 8,568). Schools were selected from the national total (response rate 82%) and age eligible children (response rate 57%) were invited to participate. Children and their parents had height and weight measurements taken using standard methods. Data were reweighted to account for the sampling design. Childhood overweight and obesity prevalence were calculated using International Obesity Taskforce definitions. Multinomial logistic regression examined the association between parent weight status, indicators of SES and child weight. Overall, 25% of children were either overweight (19.3%) or obese (6.6%). Parental obesity was a significant predictor of child obesity. Of children with normal weight parents, 14.4% were overweight or obese whereas 46.2% of children with obese parents were overweight or obese. Maternal education and household class were more consistently associated with a child being in a higher body mass index category than household income. Adjusted regression indicated that female gender, one parent family type, lower maternal education, lower household class and a heavier parent weight status significantly increased the odds of childhood obesity.

Conclusions/Significance
Parental weight appears to be the most influential factor driving the childhood obesity epidemic in Ireland and is an independent predictor of child obesity across SES groups. Due to the high prevalence of obesity in parents and children, population based interventions are required.

Background
Globally, childhood obesity is a significant public health problem associated with adverse health and economic consequences. To tackle the problem, we need a comprehensive understanding on how the environment in which we live may influence obesity related behaviours and weight status. Thus, we explore if distance to and number of food outlets ([1] supermarkets and [2] convenience stores) in the local area impact on either dietary quality or body mass index (BMI) in 9-year-old children whilst controlling for socio-economic characteristics of the family.

Methods
Cross sectional analysis of the Growing Up in Ireland (GUI) Study, a two-stage clustered sample of 8568 nine year old children from the Republic of Ireland. Children were recruited from schools (response rate 82%) and age eligible children (response rate 57%) were invited to participate. Height and weight measurements were used to calculate BMI. Diet was assessed using a short food frequency questionnaire and a dietary quality score was generated based on Irish healthy eating guidelines. Socio-economic status was measured using parent reported household class, household net equivalised income and highest level of maternal education. Food access was measured as network distance to (in quintiles) and number of (within 1000km) convenience stores and supermarkets to each participant’s household within the local area. Separate fixed effects regression models were used to assess the impact of local area food access on (1) dietary quality and (2) BMI, stratified by gender.

Results
After controlling for socio-economic characteristics of the household, distance to the nearest supermarket was not associated with dietary quality in boys (Q5 v Q1; B = 0.84, 95% CI, –0.49 to 2.18) or girls (Q5 v Q1; B = –0.41, 95% CI, –1.60 to 0.77). Distance to the nearest convenience store was associated with dietary quality in boys (Q5 v Q1; B = 1.01, 95% CI, 0.13 to 1.89) but not in girls (Q5 v Q1; B = 0.04, 95% CI, –0.71 to 0.80). The number of convenience stores or supermarkets within 1000m of the household did not impact on dietary quality. Access to food outlets was not associated with BMI in girls or boys.

Conclusion
There was little evidence to suggest that access to food stores impact dietary quality or BMI in children. From a population health perspective, strategies tackling environmental factors associated with making poor lifestyle choices are needed. Thus, further research on the association between food access and obesity risk is needed.

Background
Taking oral antibiotics during childhood has been linked with an increased risk of childhood obesity. This study assessed any potential association in number of courses of antibiotics taken between 2–3 and 4–5 years of age and body mass trajectory up to age 5.

Methods
The study was a secondary analysis of 8186 children and their parents from the infant cohort of the Irish National Longitudinal Study of Children. Antibiotic use was measured by parental recall between ages 2–3 and 4–5. Longitudinal models described the relationship between antibiotic exposure and body mass index (BMI) standard deviation scores and binary outcomes, and examined interactions between covariates, which included socioeconomic status, diet assessed by food frequency questionnaires and maternal BMI.

Results
Any antibiotic usage between 2 and 3 years did not predict risk of overweight or obesity at age 5. Four or more courses of antibiotics between 2 and 3 years were independently associated with obesity at age 5 (odds ratio 1.6, 95% confidence interval 1.11–2.31). Effect size was modest (coefficient + 0.09 body mass SD units, standard error 0.04, P = 0.037). Maternal BMI modified the relationship: ≥ 4 courses of antibiotics between 2 and 3 years were associated with a + 0.12 body mass SD units increase in weight at age 5 among children of normal-weight mothers (P = 0.035), but not in children of overweight mothers.

Conclusions
Number of antibiotic courses, rather than antibiotic use, may be an important factor in any link between early antibiotic exposure and subsequent childhood obesity. Research is needed to confirm differential effects on babies of normal versus overweight/obese mothers independent of socioeconomic factors.

Background
Orofacial clefts occur when the lips or the roof of the mouth do not fuse properly during the early weeks of pregnancy. There is strong evidence that periconceptional use of folic acid can prevent neural tube defects but its effect on oral clefts has generated debate.

Aim
To identify factors associated with suboptimal periconceptional use of folic acid and its potential effect on oral clefts.

Design and setting
The population-based infant cohort of the national Growing Up in Ireland study, which consists of 11 134 9-month-old infants.

Method
Data collection comprised questionnaires conducted by interviewers with parents in parents’ homes. Characteristics of mothers who did or did not take folic acid before and during pregnancy, as well as the effect of folic acid use on the prevalence of cleft lip and palate were recorded.

Results
The prevalence of cleft lip and palate was 1.98 (95% confidence interval [CI] = 1.31 to 2.99) per 1000 9-month-olds. The odds ratio for cleft lip was 4.36-fold higher (95% CI = 1.55 to 12.30, P = 0.005) for infants of mothers who did not take folic acid during the first 3 months of pregnancy, when compared with those who did have a folate intake during the first trimester. Folic acid use was suboptimal in 36.3% (95% CI = 35.4 to 37.2) of the sample.

Conclusion
These findings support the hypothesis that taking folic acid may partially prevent cleft lip and palate. They are particularly relevant for GPs, because they are usually the first port of call for women before and during early pregnancy.

Keywords
cleft lip, epidemiology, folic acid, general practice, infant

Growing Up in Ireland (GUI) is the national longitudinal study of children and young people in the Republic of Ireland and has followed two cohorts for over ten years to date: Cohort ’98 who were recruited into the study at age nine years and Cohort ’08, recruited at age nine months. The study aims to describe the lives of Irish children and young people in terms of their development, with a view to positively affecting policies and services available for them. Traditionally, data collection involved in-home visits from an interviewer who conducted face-to-face interviews, recorded physical measurements of study participants and administered cognitive assessments. However, with the onset of the COVID-19 pandemic and the associated restrictions, significant adaptations were required to these methods to ensure data collection for the pilot and main fieldwork for Cohort ’08 at age 13 could continue to the expected timeline. Face-to-face interviews with participants were replaced with telephone and web-based modes, interviewer training was conducted online, online resources were made available for interviewers and participants and COVID-19 related items were added to questionnaires. In addition to the scheduled data collection, a special COVID-19 survey was also conducted on both GUI cohorts in December 2020 to explore the impact of the pandemic on participants’ lives. This paper outlines the adaptations made to traditional data collection methods in GUI, highlighting the challenges that were met, but also the benefits of some changes that may be worth incorporating into future waves of GUI.

The present study investigated the home learning environment of three to five-year-old children (n = 429) living in an area designated as socio-economically disadvantaged, involved in the Area Based Childhood (ABC) programme, compared to a nationally representative sample of three-year-old children (n = 9793), from the Growing Up in Ireland (GUI) Study. Statistical analysis of the frequency of engagement in home learning activities across both samples, revealed a significant difference in the environments to which children are exposed, with families from the GUI sample engaging more frequently in these activities than families from the ABC sample. Among the family demographic factors investigated, parent’s age and household type were significantly related to the frequency of engagement in home learning activities. Based on these findings, policy and practice implications are discussed.

Keywords
home learning environment, socio-economic disadvantage, family demographics, early childhood development

Purpose
We investigated the hypothesis that mode of delivery affects childhood behavior and motor development and examined whether there are sex-specific associations, i.e., whether males and females have different risk estimates.

Methods
Families with infants born between December 2007 and May 2008 (N = 11,134) were randomly selected and recruited to the Growing Up in Ireland study. Mode of delivery was classified into spontaneous vaginal delivery; instrumental vaginal delivery; emergency Cesarean section (CS); and elective CS. The ‘Ages and Stages Questionnaire’ was completed at age 9-months and the ‘Strengths and Difficulties Questionnaire’ at 3 years. Data were weighted to represent the national sample (N = 73,662) and multivariate logistic regression was used for the statistical analyses.

Results
At age 9 months, elective CS was associated with a delay in personal social skills [adjusted odds ratio, aOR 1.24; (95 % confidence interval, CI 1.04, 1.48)] and gross motor function [aOR 1.62, (95 % CI 1.34, 1.96)], whereas emergency CS was associated with delayed gross motor function [aOR 1.30, (95 % CI 1.06, 1.59)]. At age 3 years there was no significantly increased risk of an abnormal total SDQ score across all modes of delivery.

Conclusions
Children born by elective CS may face a delay in cognitive and motor development at age 9 months. No increase in total SDQ score was found across all modes of delivery. Further investigation is needed to replicate these findings in other populations and explore the potential biological mechanisms.