United Kingdom Millennium Cohort Study Research Articles

The association between caesarean section delivery and obesity at age 17 years. Evidence from a longitudinal cohort study in the United Kingdom.

Childhood and adolescent obesity are major, preventable public health concerns. Studies to date are inconclusive regarding an association between caesarean section (CS) delivery and offspring obesity, with fewer studies conducted in late adolescence. This study examined the association between CS delivery, with a specific focus on planned CS, and induction of labour and adolescent body mass index (BMI) and body fat percentage (BF%) at age 17 years. Data on 8,880 mother-child pairs from the United Kingdom Millennium Cohort Study were analysed. The exposures were mode of delivery (normal vaginal delivery (VD) (reference), assisted VD, planned CS and emergency CS) and mode of delivery by induction of labour status. Crude and adjusted binary logistic regression and linear regression models were fitted examining BMI and BF% at age 17 years respectively, adjusting for several potential confounders. Adolescents born by CS did not have an elevated BMI or BF% compared to those born by normal VD. The fully adjusted results for overweight and obesity in children born by planned CS, compared to VD, were 1.05 (95% CI: 0.86-1.28) and 0.94 (95% CI: 0.72-1.23), respectively. The results were similar for the associations between CS and BF%, and between induction of labour and BMI. Overall, this large longitudinal study did not support an association between CS or induction of labour and overweight, obesity or BF%. It is possible that previously reported associations are due to residual or unmeasured confounding and/or underlying indications for CS delivery.

Do you like school? Social class, gender, ethnicity and pupils' educational enjoyment.

This study investigates structural inequalities in educational enjoyment in a contemporary cohort of United Kingdom (UK) primary school children. Foundational studies in the sociology of education consistently indicate that the enjoyment of education is stratified by social class, gender, and ethnicity. Analysing data from the UK Millennium Cohort Study, which is a major cohort study that tracks children born at the start of the 21st century, we examine children's enjoyment of both school and individual academic subject areas. The overarching message is that at age 11 most children enjoy their education. The detailed empirical analyses indicate that educational enjoyment is stratified by gender, and there are small differences between ethnic groups. However, there is no convincing evidence of a social class gradient. These results challenge orthodox sociological views on the relationship between structural inequalities and educational enjoyment, and therefore question the existing theoretical understanding of the wider role of enjoyment in education.

Associations between Gross and Fine Motor Skills, Physical Activity, Executive Function, and Academic Achievement: Longitudinal Findings from the UK Millennium Cohort Study.

Accumulating evidence from behavioral studies and neuroscience suggests that motor and cognitive development are intrinsically intertwined. To explore the underlying mechanisms of this motor-cognition link, our study examined the longitudinal relationship of early motor skills and physical activity with later cognitive skills. The sample was 3188 children from the United Kingdom Millennium Cohort Study, followed at 9 months and 5, 7, and 11 years. Early motor skills were examined at 9 months. Children's daily physical activity level was measured using accelerometers at 7 years and a questionnaire was conducted at 11 years. Cognitive skills, including executive function and academic achievement, were measured at age 11. The results suggest that gross motor skills were positively associated with spatial working memory, whereas fine motor skills were predictive of good English and science outcomes. Moderate-to-vigorous activity was found to be negatively associated with English performance, although self-reported activity frequency was positively linked to math. Our results highlight the significant role of both gross and fine motor skills in cognitive development. This study also elucidates the limitations of using activity intensity to assess the impact of motor activity on children's cognitive development, suggesting that attention to the effects of specific types of physical activity would better elucidate the motor/cognition link.

Risk factors of persistent adolescent thinness: findings from the UK Millennium Cohort Study

BackgroundThinness during adolescence can increase the risk of adverse health outcomes across the life-course and impede development. There is limited research examining the prevalence and determinants of persistent adolescent thinness in the United Kingdom (UK). We used longitudinal cohort data to investigate determinants of persistent adolescent thinness.MethodsWe analyzed data from 7,740 participants in the UK Millennium Cohort Study at ages 9 months, 7, 11, 14 and 17 years. Persistent thinness was defined as thinness at ages 11, 14 and 17; thinness was defined as an age- and sex-adjusted Body Mass Index (BMI) of less than 18.5 kg/m2. In total, 4,036 participants, classified either as persistently thin or at a persistent healthy weight, were included in the analyses. Logistic regression analyses were conducted to examine associations between 16 risk factors and persistent adolescent thinness by sex.ResultsThe prevalence of persistent thinness among adolescents was 3.1% (n = 231). Among males (n = 115), persistent adolescent thinness was significantly associated with non-white ethnicity, low parental BMI, low birthweight, low breastfeeding duration, unintended pregnancy, and low maternal education. Among females (n = 116), persistent adolescent thinness was significantly associated with non-white ethnicity, low birthweight, low self-esteem, and low physical activity. However, after adjusting for all risk factors, only low maternal BMI (OR: 3.44; 95% CI:1.13, 10.5), low paternal BMI (OR: 22.2; 95% CI: 2.35, 209.6), unintended pregnancy (OR: 2.49; 95% CI: 1.11, 5.57) and low self-esteem (OR: 6.57; 95% CI: 1.46,29.7) remained significantly associated with persistent adolescent thinness among males. After adjustment for all risk factors, not reaching the recommended physical activity levels (OR: 4.22; 95% CI: 1.82, 9.75) remained significantly associated with persistent adolescent thinness among females. No appreciable associations were found between persistent adolescent thinness and sex, premature birth, smoking during pregnancy, income, maternal postnatal depression, mother-infant attachment or socio-emotional difficulties (p > 0.05).ConclusionPersistent adolescent thinness is not rare and appears to be associated with both physical and mental health factors, with some sex specific differences. Healthy weight initiatives should consider the full weight spectrum. Further research is required to understand thinness at a population level, including among those whose BMI changes during child and adolescent development.

The role of energy balance related behaviors in socioeconomic inequalities in childhood body mass index: A comparative analysis of Germany, the Netherlands, the United Kingdom, and the United States

Socioeconomic inequalities in childhood Body Mass Index (BMI) are becoming increasingly more pronounced across the world. Although countries differ in the direction and strength of these inequalities, cross-national comparative research on this topic is rare. This paper draws on harmonized longitudinal cohort data from four wealthy countries—Germany, the Netherlands, the United Kingdom (UK), and the United States (US)—to 1) map cross-country differences in the magnitude of socioeconomic inequalities in childhood BMI, and 2) to examine cross-country differences in the role of three energy-balance-related behaviors—physical activity, screen time, and breakfast consumption—in explaining these inequalities. Children were aged 5–7 at our first timepoint and were followed up at age 8–11. We used data from the German National Educational Panel Study, the Dutch Generation R study, the UK Millennium Cohort Study and the US Early Childhood Longitudinal-Kindergarten Study. All countries revealed significant inequalities in childhood BMI. The US stood out in having the largest inequalities. Overall, inequalities between children with low versus medium educated parents were smaller than those between children with high versus medium educated parents. The role of energy-balance-related behaviors in explaining inequalities in BMI was surprisingly consistent. Across countries, physical activity did not, while screen time and breakfast consumption did play a role. The only exception was that breakfast consumption did not play a role in the US. Cross-country differences emerged in the relative contribution of each behavior in explaining inequalities in BMI: Breakfast consumption was most important in the UK, screen time explained most in Germany and the US, and breakfast consumption and screen time were equally important in the Netherlands. Our findings suggest that what constitutes the most effective policy intervention differs across countries and that these should target both children from medium as well as low educated families.

Is Motor Milestone Assessment in Infancy Valid and Scaled Equally Across Sex, Birth Weight, and Gestational Age? Findings From the Millennium Cohort Study.

Is the assessment of motor milestones valid and scaled equivalently for all infants? It is not only important to understand if the way we use gross and fine motor scores are appropriate for monitoring motor milestones but also to determine if these scores are confounded by specific infant characteristics. Therefore, the aim of the study is to investigate the latent structure underlying motor milestone assessment in infancy and measurement invariance across sex, birth weight, and gestational age. For this study, the birth cohort data from the United Kingdom Millennium Cohort Study (MCS) was used, which includes the assessment of eight motor milestone tasks from the Denver Developmental Screening Test in 9-month-old infants (N = 18,531), depicting early motor development of the first children of generation Z. Confirmatory factor analyses showed a better model fit for a two-factor structure (i.e., gross and fine motor development) compared to a one-factor structure (i.e., general motor development), and multiple indicators multiple causes modeling revealed no differential item functioning related to sex, birth weight, and gestational age. The study provides support for the use of gross and fine motor scores when assessing motor milestones in infants—both boys and girls with different birth weights and of varying gestational ages. Further investigation into widely adopted assessment tools is recommended to support the use of valid composite scores in early childhood research and practice.

Early-life maternal attachment and risky health behaviours in adolescence: findings from the United Kingdom Millennium Cohort Study

BackgroundEarly uptake of multiple risky behaviours during adolescence, such as substance use, antisocial and sexual behaviours, can lead to poor health outcomes without timely interventions. This study investigated how early-life maternal attachment, or emotional bonds between mothers and infants, influenced later risky behaviours in adolescence alongside other potential explanatory pathways using the United Kingdom Millennium Cohort Study.MethodsTotal maternal attachment scores measured at 9 months using the Condon (1998) Maternal Postnatal Attachment Scale compared higher and lower attachment, where mothers in the lowest 10th percentile represented lower attachment. Multiple risky behaviours, defined as two or more risky behaviours (including smoking cigarettes, vaping, alcohol consumption, illegal drug use, antisocial behaviour, criminal engagement, unsafe sex, and gambling), were scored from 0 to 8 at age 17. Five multivariate logistic regression models examined associations between maternal attachment and multiple risky behaviours among Millennium Cohort Study members (n = 7796). Mediation analysis sequentially adjusted for blocks of explanatory mechanisms, including low attachment mechanisms (multiple births, infant prematurity, sex, breastfeeding, unplanned pregnancy and maternal age at birth), maternal depression, and social inequalities (single-parent status, socioeconomic circumstance by maternal education and household income) at 9 months and poor adolescent mental health at 14 years.ResultsChildren of mothers with lower maternal attachment at 9 months had 23% increased odds of multiple risky behaviours at 17 years (OR: 1.23, 95% CI: 1.00–1.50) in the unadjusted baseline model. All five explanatory blocks attenuated baseline odds. Low attachment mechanisms attenuated 13%, social inequalities 17%, and poor mental health 17%. Maternal depression attenuated the highest proportion (26%) after fully adjusting for all factors (30%).ConclusionsLower maternal attachment in early life predicted increased adolescent multiple risky behaviours. Almost a third of the excess risk was attributable to child, maternal and socioeconomic factors, with over a quarter explained by maternal depression. Recognising the influence of early-life risk factors on adolescent health could innovate current policies and interventions addressing multiple risky behaviour uptake affecting health inequalities across the life course.

Internalized weight bias in the relationship between mental health and obesity in UK adolescents

Abstract Background It is crucial to promote mental and physical health during adolescence to protect against lifetime risks of mental health problems and obesity. Internalized weight bias (self-directed stigmatizing attitudes about perceived weight status) and bullying are implicated as potential mechanisms in the relationship between mental health and obesity in adolescence. We examined internalized weight bias and bullying as potential mediators of the relationship between mental health and weight status across adolescence in the United Kingdom (UK). Methods We analysed data on 8,688 adolescents from the UK Millennium Cohort Study. Weight status was defined using sex and age specific International Obesity Taskforce cut points for body-mass index (not overweight/obese; overweight; obese) at 11 and 17 years. Mental health was defined using parental reported emotional (anxiety and depression), and externalizing (aggression and impulsivity) symptoms at 11 and 17 years (low; moderate; high). Self-reported measures of internalized weight bias captured via body-dissatisfaction and self-esteem and bullying at 14 years were tested as mediators. We used Generalized Structural Equation Models to examine longitudinal pathways between weight status and mental health across 11 and 17 years, whilst accounting for concurrent associations and potential confounders. Results Adolescents with high emotional (relative risk (RR) 1.98, 95% CI 1.28 to 3.07) or externalizing symptoms (RR 2.07, 95% CI 1.23 to 3.48) at 11 years were twice as likely to be obese at 17 years compared with those who had low symptoms. The impact of emotional and externalizing symptoms on weight status was found to be partially attributable to internalized weight bias, but not bullying, with significant mediation for body-dissatisfaction and low self-esteem. Conclusions Internalized weight bias partially explains the relationship between mental health and weight status across adolescence. Key messages There is a need for a holistic, early prevention strategy to focus on reducing weight stigma to encourage healthy mental and physical development of children. The relationship between mental health and weight status across adolescence is partly attributable to internalized weight bias.

Police Stops and Adolescent Substance Use: Findings From the United Kingdom Millennium Cohort Study

PurposeThe aim of this study is to investigate associations between police stops and adolescent substance use among a large, representative sample of adolescents in the United Kingdom (UK). MethodsData from the three most recent sweeps of the UK Millennium Cohort Study, a nationally representative contemporary birth cohort of children born in the UK between September 2000 and January 2002, were analyzed in 2021 (N = 10,345). Lifetime police stops are assessed at age 14 (Sweep 6, 2015) and a diverse set of adolescent substance use behaviors are assessed at age 17 (Sweep 7, 2018). Weights are used to account for sample design and multiple imputation for missing data. ResultsYouth experiencing police stops by the age of 14 (14.72%) reported significantly higher engagement in substance use behaviors at age 17, including frequent binge drinking (adjusted relative risk ratio [ARRR] = 3.56, confidence interval [CI] = 2.80–4.03), cigarette use (ARRR = 3.97, CI = 3.26–4.84), e-cigarette use (ARRR = 2.22, CI = 1.69–2.93), cannabis use (ARRR = 3.63, CI = 2.88–4.57), and illicit drug use (adjusted incidence rate ratio = 3.06, CI = 2.45–3.81). Ancillary analyses revealed that findings linking police stops to substance use emerge across distinct stop features (e.g., questioned vs. warned), following adjustment for substance use at age 14, and when examining substance use initiation after the age of 14. ConclusionsPolice officers should be trained to effectively communicate and interact with youth to mitigate adverse sequelae of stops. Youth may also benefit from mental health and substance use screenings as well as counseling care following these events.

Pubertal Timing and Adolescent Alcohol Use: The Mediating Role of Parental and Peer Influences.

Using intergenerational, prospective data at ages 9months, 7, 11, and 14years from the nationally representative United Kingdom Millennium Cohort Study, this interdisciplinary study unpacks why 14-year-old adolescents with early perceived pubertal timing (PT) were more likely to drink alcohol (ever, frequent, and binge drinking) compared to those whose PT was on-time or late (5,757 girls, 5,799 boys; 80% White, 10% Asian, 3% Black, and 7% Other British). Parents allowed drinking among 22% (18%) of early PT girls (boys) compared to 11% of late PT adolescents; formal mediation models showed differences by PT in parent permissiveness and gains in alcohol-using friends primarily explained age 14 PT-drinking associations. Parental alcohol permissiveness should be a key prevention target for early PT adolescents.

Caesarean section delivery and childhood obesity in a British longitudinal cohort study.

Several studies reported an association between Caesarean section (CS) birth and childhood obesity. However, there are several limitations in the current literature. These include an inability to distinguish between planned and emergency CS, small study sample sizes and not adjusting for pre-pregnancy body-mass-index (BMI). We examined the association between CS delivery and childhood obesity using the United Kingdom Millennium Cohort Study (MCS). Mother-infant pairs were recruited into the MCS. Use of sampling weights ensured the sample was representative of the population. The exposure was categorised as normal vaginal delivery (VD) [reference], assisted VD, planned CS and emergency CS. Childhood obesity prevalence, at age three, five, seven, eleven and fourteen years was calculated using the International Obesity Taskforce criteria. Mixed-effects linear regression models were fitted with associations adjusted for several potential confounders like maternal age, pre-pregnancy BMI, education and infant macrosomia. Linear regression models were fitted evaluating body fat percentage (BF%), at age seven and fourteen years. Of the 18,116 infants, 3872 (21.4%) were delivered by CS; 9.2% by planned CS. Obesity prevalence was 5.4%, 5.7%, 6.5%, 7.1% and 7.6% at age three, five, seven, eleven and fourteen years respectively. The mixed-effects linear regression model showed no association between planned (adjusted mean difference = 0.00; [95% confidence interval (CI) -0.10; 0.10], p-value = 0.97) or emergency CS (adjusted mean difference = 0.08; [95% CI -0.01; 0.17], p-value = 0.09) and child BMI. At age seven years, there was no association between planned CS and BF% (adjusted mean difference = 0.13; [95% CI -0.23; 0.49]); there was no association at age fourteen years. Infants born by planned CS did not have a significantly higher BMI or BF% compared to those born by normal VD. This may suggest that the association, described in the literature, could be due to the indications/reasons for CS birth or residual confounding.

Household income and sticky floors in children’s cognitive development: Evidence from the United Kingdom Millennium Cohort Study

While there is a rich literature on the socio-economic gaps in children’s average cognitive test scores in the United Kingdom, there is less evidence on the differences in children’s transitions along the ability distribution. Using data from five sweeps of the UK Millennium Cohort Study at the ages of 9 months, 3 years, 5 years, 7 years and 11 years, this paper analyses the role of household income, relative to other socio-economic factors, in influencing children’s chances of moving up or down the age-specific cognitive ability distribution as they grow older. Descriptive findings indicate a high level of variability between ages 3 and 11, but children from income-poor households are more likely to get trapped in the bottom of the age-specific cognitive ability distribution. Event history analysis shows that household income protects children from falling into the lowest-performing group without necessarily helping existing low performers improve. In contrast, parental education both protects children from slipping into low performance and helps them move up if they fall into it. While this is, perhaps, disheartening because household income is more amenable to policy than parental education, there is potential for income-enhancing policies to protect children from scoring poorly in the first place.

Arts engagement and self-esteem in children: results from a propensity score matching analysis.

Self‐esteem is regarded as vital to children's social and cognitive development and emotional well‐being. To date, a few studies have suggested that arts activities can improve self‐esteem in young people. However, such studies mainly focused on small, nonrepresentative samples. In this study, data from 6209 children included in the United Kingdom Millennium Cohort Study were analyzed using propensity score matching to investigate the association between children's arts engagement ((1) listening to or playing music; (2) drawing, painting, or making things; and (3) reading for enjoyment) and self‐esteem at age 11. All three activities were associated with higher levels of self‐esteem when matching for all identified demographic, socioeconomic, and familial confounders. Additionally, the relationship was more prominent when children engaged in these activities with their parents on a regular basis. However, there was no clear evidence that ability in either music or arts activities moderated the relationship with self‐esteem, although English language ability may moderate the association between reading and self‐esteem. These results suggest that initiatives to promote arts engagement in children may provide a practical and efficient way to improve children's self‐esteem. This is the key given self‐esteem in childhood tends to decline as children enter adolescence, yet is linked to lifelong development and well‐being.

Social Disadvantage, Maternal Psychological Distress, and Difficulties in Children's Social-Emotional Well-Being.

This study used data from wave four of the United Kingdom (U.K.) Millennium Cohort Study to examine whether there is an individual (i.e., maternal education) and area-level social disadvantage (i.e., neighborhood deprivation) gradient to difficulties in social-emotional well-being (SEW) in 7-year-old English children. We then investigated to what extent maternal psychological distress (Kessler 6 score) explains the relationship between social disadvantage indicators and boys’ and girls’ SEW difficulties. Subjects consisted of 3661 child–mother dyads (1804 boys and 1857 girls). Results discerned gender differences in the effect social disadvantage indicators have on child SEW difficulties. Maternal education had a comparable effect on boys’ and girls’ SEW difficulties, but a steeper neighborhood deprivation gradient was evident for boys’ SEW difficulties compared to girls’ SEW difficulties. The effect of each social disadvantage indicator on boys’ and girls’ SEW difficulties was for most part direct and strong (p ≤ 0.001) rather than through maternal psychological distress, suggesting that the theoretical framework was incomplete. Here we demonstrate that where children are positioned on the social disadvantage gradient matters greatly to their SEW. Improving the living conditions and health of mothers with psychological distress may offer a pathway to improve child SEW.

Air Pollution and Cognitive Development in Children of United Kingdom Millennium Cohort Study

Background/Aim: There is increasing interest in the possible link between air pollution and cognitive development, but the evidence remains inconclusive. We investigated the association between long-term exposure to air pollution and cognitive development in children in the United Kingdom’s Millennium Cohort Study (MCS). Methods: The MCS follows children born in 2000-01, ~13,000 of whom (England 63%, Wales 15%, Scotland 11% and Northern Ireland 10%) were assessed for cognitive development. We linked each child to the annual mean concentration of PM2.5, PM10, NO2 and SO2 at the postcode centroid for his/her home address at the time of assessment. Cognitive function was assessed at age 3, 5 and 7 years using the British Ability Scales (BAS) and National Foundation for Education Research methods. Age-normalized T-scores of each domain (two domains at age 3, three each at ages 5 and 7), and their changes over time, were analysed by multiple linear regression with adjustment for sex, ethnicity, socioeconomic status and country/region, and allowing for clustering by local authority or district. Results: In England, a 10µg/m3 increase in PM2.5, PM10 and NO2 was associated with a change of -5.2 (95%CI: -7.4, -2.9), -3.7 (-5.2, -2.3) and -1.1 (-1.6, -0.5) in Naming Vocabulary score at age 5, but small (not statistically significant) changes in the two other domains. At age 7, a 10µg/m3 increase in PM2.5 was associated with a change of -2.8 (-5.5, -0.1) in Pattern Construction scores, but no other pollutant-outcome combination showed evidence of adverse association. Results for Scotland were broadly similar to those for England, but somewhat different in Wales and Northern Ireland. Conclusions: Higher PM2.5, PM10 and NO2 concentration was associated with lower cognitive ability in selected cognitive assessments at ages 5 and 7, but not consistently so in all countries of the United Kingdom and at all ages.

Parental breakup and children’s development: the role of time and of post-separation conditions

In recent years, the relationship between parental separation and child outcomes has received massive attention. This extraordinary level of interest stems from the rise in divorce rates in almost all developed countries. The aim of the paper is to identify the effect of parental separation on child cognitive and behavioural outcomes. It uses data on a sample of around 9000 children up to age 11, drawn from five waves of the United Kingdom Millennium Cohort Study. We use fixed-effects models to control for unobservable characteristics that do not vary over time, and explore the role of time and of post-separation conditions in mitigating these effects. We find that parental separation has detrimental but small effects on children’s behaviours, and that these effects appear stronger after a couple of years from separation. An intimate relationship between the child and the non-resident father, the presence of a new mother’s partner and of other relatives also play a role. No effect is found on cognitive development.

Support for new mothers and fertility in the United Kingdom: Not all support is equal in the decision to have a second child

Low fertility across Europe highlights the need to understand reproductive decisions in high-income countries better. Availability of support may be one factor influencing reproductive decisions, though within high-income countries availability varies between environments, including socio-economic environments. We test whether receiving higher levels of support, from different sources (informal and formal) and of different types (practical and emotional), is positively correlated with second births in the United Kingdom (UK) Millennium Cohort Study, and whether these relationships differ by socio-economic position (SEP). Our hypothesis is only partially supported: receiving emotional support correlates with higher likelihood of second birth, but the opposite is true for practical support. Availability of different types of support varies across SEP, but relationships between support and fertility are similar, with one exception: kin-provided childcare increases the likelihood of birth only among lower-SEP women. Our results highlight that not all support is equal in the decision to have a second child.

Bi-directional relationships between body mass index and height from three to seven years of age: an analysis of children in the United Kingdom Millennium Cohort Study

Adiposity and height are known to correlate in childhood but it is less clear whether height and weight gain occur in synergy. We investigate the bidirectional relationships between measures of height and body mass index (BMI) – an indicator of adiposity – and their rates of change. The sample comprises singleton children in the Millennium Cohort Study (N = 11,357). Child anthropometrics measured by trained interviewers at ages three, five and seven years (2003-2009) were transformed to standardised scores based on 1990 British Growth Reference data from which piecewise linear models for height and BMI were jointly fitted. At three years of age, zHeight was positively related to subsequent zBMI velocities, whereas zBMI at three years was positively related to zHeight velocity to age five but inversely related to zHeight velocity from five to seven years of age. Age three zBMI predicted zHeight velocity from three to five years more strongly than age three zHeight predicted zBMI velocity over the same period. The rate of change in zHeight was positively correlated with subsequent zBMI velocity and vice versa. This new evidence on the bidirectional relationships between height and BMI velocities sheds light on the early childhood origins of obesity in adulthood and the need to monitor growth as well as weight gain.

Involvement With Past‐Union Children and Couple Childbearing Intentions

Parents with children from both past and current unions create complex stepfamilies. The author investigated the association of past‐union children with intentions for a second or third child in the current union of 1,739 couples in the United Kingdom Millennium Cohort Study. Both partners' reports of their own resident and nonresident past‐union children as well as fathers' reports of involvement with nonresident past‐union children create a comprehensive measurement of past‐union children. The analysis revealed that coresident past‐union children were more closely associated with childbearing intentions than were nonresident past‐union children and that weekly contact with nonresident children had a stronger link to intentions than did payments. These results suggest that the value of the past‐union children as siblings and the time commitment made to these children are particularly salient to parents' decisions about further childbearing in their current union.

Timing of Prenatal Smoking Cessation or Reduction and Infant Birth Weight: Evidence from the United Kingdom Millennium Cohort Study

Smoking during pregnancy is a key contributor to poor infant health. Our study presents a dynamic relationship between the timing of prenatal smoking cessation or reduction and infant birth weight. Using a large representative dataset of a birth cohort in the United Kingdom, we apply regression analysis to examine the influences of cessation in smoking or reduction in smoking intensity at different months or trimesters on infant birth weight. For robustness checks, we use a rich set of additional covariates, a series of variable selection procedures, alternative birth outcome measures, and stratified samples. We find robust evidence that mothers who quit smoking by the third month of pregnancy or the end of the first trimester have infants of the same weight as those infants of nonsmokers. However, we find smoking cessation in the fourth month or any time beyond is associated with substantially lower infant birth weights. Two-thirds of the total adverse smoking impact on infant birth weight occurs in the second trimester. Our study also shows mothers who smoke throughout pregnancy but cut smoking intensity by the third month in pregnancy deliver infants of the same weight as those infants born to persistent light smokers. Our research suggests the efficacy of prenatal smoking cessation services can be significantly improved, if health professionals can encourage more pregnant women to quit smoking or reduce smoking intensity timely by the end of the first trimester.