Maternal smoking during pregnancy and offspring smoking initiation: assessing the role of intrauterine exposure

Assessing Causality Between Second-Hand Smoking and Potentially Associated Diseases in Multiple Systems: A Two-Sample Mendelian Randomization Study

INTRODUCTION

The global disease burden may be exacerbated by exposure to passive smoking (SHS), with the workplace being a primary location for such exposure. Numerous epidemiological studies have identified SHS as a risk factor for diseases affecting various systems, including cardiovascular, respiratory, immune, endocrine, and nervous systems. The conventional observational study has certain methodological constraints that can be circumvented through a Mendelian randomization (MR) study. Our MR study intends to investigate the causal link between workplace exposure to SHS and the potential associated diseases.

AIM AND METHODS

Summary statistics data involving European participants were sourced from three databases: the UK Biobank, the FinnGen study, and the European Bioinformatics Institute. Genetic variants linked with exposure to SHS in the workplace were identified as instrumental variables. The MR was carried out using inverse variance weighted (IVW), MR-Egger, and weighted median methods. Sensitivity tests were also undertaken within the MR to evaluate the validity of the causality.

RESULTS

According to the IVW model, genetically determined atrial fibrillation (AF) and stroke (p = 6.64E-04 and 5.68E-07, odds ratio = 2.030 and 2.494, 95% confidence interval = 1.350 to 3.051 and 1.743 to 3.569) were robustly associated with exposure to SHS in the workplace. Suggestive associations were found between workplace SHS and myocardial infarction (MI), asthma, and depression.

CONCLUSIONS

The MR study demonstrates that exposure to SHS in the workplace is a significant risk factor for AF and stroke in European individuals. Whether workplace exposure to SHS influences other diseases and the causality between them requires further exploration.

IMPLICATIONS

This study explored the causality between exposure to SHS in the workplace and potential associated diseases in multiple systems, including MI, AF, stroke, lung cancer, asthma, allergic disease, type 2 diabetes, and depression, using an MR study. The MR study can circumvent the methodological constraints of observational studies and establish a causal relationship. The two-sample MR analysis provides evidence supporting the causal association of frequent workplace SHS with AF and stroke. Individuals exposed to SHS in the workplace may also have a heightened risk of MI, asthma, and depression. However, whether SHS affects other diseases and the causality between them requires further investigation. To our knowledge, this is the first two-sample MR study to determine the causal relationship between SHS and potential diseases. Exposure to SHS in the workplace is a prevalent issue and may contribute to a global disease burden. The reduction of exposure following the introduction of smoke-free laws has led to a decrease in the admission rate for cardiac events and an improvement in health indicators. It is crucial to further advance smoke-free policies and their implementation.

Methodological approaches, challenges, and opportunities in the application of Mendelian randomisation to lifecourse epidemiology: A systematic literature review

Diseases diagnosed in adulthood may have antecedents throughout (including prenatal) life. Gaining a better understanding of how exposures at different stages in the lifecourse influence health outcomes is key to elucidating the potential benefits of disease prevention strategies. Mendelian randomisation (MR) is increasingly used to estimate causal effects of exposures across the lifecourse on later life outcomes. This systematic literature review explores MR methods used to perform lifecourse investigations and reviews previous work that has utilised MR to elucidate the effects of factors acting at different stages of the lifecourse. We conducted searches in PubMed, Embase, Medline and MedRXiv databases. Thirteen methodological studies were identified. Four studies focused on the impact of time-varying exposures in the interpretation of "standard" MR techniques, five presented methods for repeat measures of the same exposure, and four described methodological approaches to handling multigenerational exposures. A further 127 studies presented the results of an applied research question. Over half of these estimated effects in a single generation and were largely confined to the exploration of questions regarding body composition. The remaining mostly estimated maternal effects. There is a growing body of research focused on the development and application of MR methods to address lifecourse research questions. The underlying assumptions require careful consideration and the interpretation of results rely on select conditions. Whilst we do not advocate for a particular strategy, we encourage practitioners to make informed decisions on how to approach a research question in this field with a solid understanding of the limitations present and how these may be affected by the research question, modelling approach, instrument selection, and data availability.

Intergenerational transmission of tobacco smoking: The role of the child's behavioral difficulties. Data from the Danish National Birth cohort (DNBC)

AIMS

This study explores the role of offspring behavioral difficulties in the intergeneration transmission of tobacco smoking.

METHODS

This longitudinal cohort study is based on children born in Denmark in 1996-2003 participating in the Danish National Birth Cohort (DNBC), followed-up until 18years of age. We included mother-child pairs with complete data regarding the exposure (4 trajectories of maternal daily smoking quantity during pregnancy: low, intermediate/stable, intermediate/decreasing and high), outcome (offspring daily smoking status at 18 years) and mediator (offspring symptoms of hyperactivity-inattention at 11 years), that is 24,588 mother-child pairs.

RESULTS

In our study population, during pregnancy respectively 86.2%, 6.80%, 4.08% and 2.97% mothers belonged to the low, intermediate/stable, intermediate/decreasing and high smoking trajectory groups. After controlling for covariates using propensity scores, the direct effect of maternal smoking in pregnancy on offspring smoking in adolescence was statistically significant, especially when the mother belonged to the intermediate/stable smoking trajectory group (ORIPW = 2.09, 95% CI: 1.70 - 2.61) or to the high smoking trajectory group (ORIPW = 2.08, 95% CI: 1.52 - 3.11) compared to the low smoking trajectory group. None of the indirect effects of maternal smoking in pregnancy were statistically significant, and neither were the proportions mediated.

CONCLUSION

Maternal pregnancy smoking seems to have an influence on offspring smoking in early adulthood, which does not appear to be mediated by offspring behavioral difficulties. Women should be strongly encouraged to quit smoking in pregnancy to reduce both short and long-term health risks among their offspring.

Associations of timing, level, and pattern of secondhand smoke exposure with early alcohol initiation: A cohort study

BACKGROUND

Few studies explored the longitudinal link between early-life secondhand smoke (SHS) exposure and later alcohol initiation despite its risk for child behavioral difficulties. We examined the associations of the timing, level, and pattern of SHS exposure from pregnancy to childhood with early alcohol initiation and evaluated the sex differences in these associations.

METHODS

Data were from 16,440 participants of the Taiwan Birth Cohort Study conducted when the children were aged 6 months, 18 months, 3 years, 5.5 years, 8 years, and 12 years. Group-based trajectory modeling was applied to identified patterns of SHS exposure. A series of multiple logistic regression were conducted to examine study hypotheses.

RESULTS

Exposure to prenatal SHS was associated with an increased risk of early alcohol initiation (adjusted odds ratio [aOR] = 1.17, 95% confidence interval [CI] = 1.06, 1.30). Compared with the adolescents with a persistent-low-exposure trajectory, those who exhibited prenatal-high-decreasing (aOR = 1.18, 95% CI = 1.04, 1.35) or persistent-high-exposure (aOR = 1.27, 95% CI = 1.12, 1.45) patterns exhibited increased risks of early alcohol initiation. Those with higher cumulative levels of SHS exposure also exhibited an increased risk of early alcohol initiation (aOR = 1.03, 95% CI = 1.01, 1.04). Sex differences were also observed.

CONCLUSIONS

Varying timing, levels, and longitudinal patterns of SHS exposure during early life had differential effects on early alcohol initiation, with the effects differing by sex. Targeting SHS exposure while considering the nature of exposure and sex differences could help prevent and curb alcohol use in adolescents.

Family functioning and nicotine dependence among smoking fathers: a cross-sectional study

BACKGROUND

Nicotine dependence is a significant public health issue, and understanding the factors associated with nicotine dependence in this population is crucial for developing effective interventions. This study examined the association between family functioning and nicotine dependence levels of smoking fathers based on the McMaster model of family functioning (MMFF), providing evidence for future interventions.

METHODS

In this study, we selected fathers of first- to fifth-grade students from 10 pilot elementary schools in Qingdao whose families smoked. We used the Fagerstrom test to assess nicotine dependence and the Family Assessment Device to evaluate family functioning. We performed univariate analysis to compare differences among those with different levels of nicotine dependence, and we used an ordinal logistic regression analysis to investigate the influences related to nicotine dependence.

RESULTS

This study included 874 smokers, with 78.5% having mild nicotine dependence, 11.7% having moderate dependence, and 9.84% having severe dependence. Univariate analysis showed that smokers with severe dependence had lower education levels, higher prevalence of chronic diseases, more frequent alcohol consumption, and poorer family functioning compared to those with mild to moderate dependence. Ordinal logistic regression analysis showed that poorer general functioning scores (OR = 1.087, 95% CI: 1.008-1.173, P = 0.030), poorer behavioral control (OR = 1.124, 95% CI: 1.026-1.232, P = 0.012), more quit attempts, frequent alcohol consumption, and longer smoking duration may be associated with a higher likelihood of developing severe nicotine dependence. The older age of starting smoking and higher education level may be associated with a lower likelihood of developing severe nicotine dependence. However, it is important to note that the cross-sectional nature of this study precludes the determination of causal relationships.

CONCLUSIONS

This study finds that heavy nicotine dependence in smoking fathers is associated with risky behaviors and demographics such as longer smoking duration and frequent alcohol consumption. Targeted smoking cessation interventions are crucial for this group, taking these specific factors into consideration. Family functioning, particularly general functioning and behavioral control, may also be linked to nicotine dependence, indicating the need for further research in this area.

The association of maternal sugary beverage consumption during pregnancy and the early years with childhood sugary beverage consumption

OBJECTIVES

A woman's food choices during pregnancy may be associated with her offspring's food choices. Several studies support an association between childhood sugary beverage (SB) consumption and poor cardiometabolic health. This study aimed to assess the association of maternal SB consumption during pregnancy and later, with her offspring's SB consumption in early infancy and childhood.

METHODS

A total of 1945 women and 1595 children participating in 3 Canadian studies reported SB consumption during pregnancy, at 2 years of age, and/or at school age (5 to 8 years old). Mother and offspring SB intakes were self-reported by mothers. Multivariable linear regression analyses were conducted within each cohort and cohort data were combined using fixed effect meta-analyses.

RESULTS

Maternal SB consumption during pregnancy was associated with higher offspring SB consumption at 2 years of age (standardized β = 0.19 predicted change in the number of standard deviations of offspring SB intake for an increase of 1 standard deviation in maternal serving [95% CI: 0.16 to 0.22]). Concurrent maternal SB consumption was associated with higher offspring SB intake when children were aged 5 to 8 years (standardized β= 0.25 [95% CI: 0.10 to 0.40]).

CONCLUSION

Maternal SB consumption during pregnancy is associated with a marginally higher SB intake among their offspring at age 2, and concurrent maternal consumption is associated with a higher SB intake among school-aged offspring (5 to 8 years old). Future interventions tailored for pregnancy and early childrearing years to reduce SB intakes of mothers may reduce young children's SB intake.

The Relationship of Tobacco Use and Migraine: A Narrative Review

PURPOSE OF REVIEW

Tobacco use is associated with significant health consequences especially for people with medical conditions. Although lifestyle strategies (e.g., sleep, diet) are commonly recommended as part of migraine treatment, tobacco-related strategies (e.g., smoking cessation) are rarely included. This review is aimed at elucidating what is known about tobacco use and migraine and at identifying gaps in the research.

RECENT FINDINGS

The prevalence of smoking is higher among people with migraine, and people with migraine believe that smoking makes migraine attacks worse. There is also evidence that smoking may exacerbate migraine-related consequences (e.g., stroke). Very few studies have examined other aspects of smoking and migraine or tobacco products other than cigarettes. There are significant gaps in our knowledge of smoking and migraine. More research is needed to understand the relationship of tobacco use to migraine and potential benefits of adding smoking cessation efforts into migraine care.

Maternal smoking around birth may lower the protective effects of breastfeeding on anxiety, depression and neuroticism in adult offspring: a UK biobank study

We aim to explore the combined effects of the smoking and breastfeeding on offspring mental health outcomes. We used data from UK biobank (N = 342,846) to evaluate joint effect of breastfeeding and maternal smoke during pregnancy (MSDP) on seven adult offspring mental health outcomes (self-reported depression, depression score, self-reported anxiety, anxiety score, neuroticism score, self-harm, suicide). We stratified individuals to MSDP group and non-MSDP group as well as breastfeeding group and non-breastfeeding group. Multiple linear regression and logistic regressions analysis were performed between independent variables (MSDP or breastfeeding) and dependent variables separately (seven mental health outcomes) in each stratum. Effect estimates were expressed as β values and OR values. Sex, age, 10 principle components of population structure, smoking, alcohol use, and Townsend deprivation index were examined as covariates. At MSDP grouping level, coefficients (odds ratio [OR]) for association of breastfed as a baby with self-reported anxiety (category variable) were 0.87 (95%CI, (0.82-0.93), P = 1.74 × 10^-5) in the MSDP group and 0.83 (95%CI, (0.79-0.87), P = 2.76 × 10^-17) in the non-MSDP group. At breastfeeding grouping level, OR for association of MSDP and self-reported anxiety were 1.15 (95%CI, (1.10-1.20), P = 5.36 × 10^-11) in breastfeeding group and 1.12(95%CI, (1.06-1.20), P = 2.02 × 10^-4) in non-breastfeeding group. At MSDP grouping level, negatively associations were found for breastfeeding and anxiety score (continuable variable) in MSDP group (-0.04 SD change per SD change in MSDP, 95% CI, (- 0.06, - 0.02), P = 2.42 × 10^-3) and non-MSDP group (-0.06 SD change per SD change in MSDP, 95%CI, (- 0.07, - 0.04), P = 1.70 × 10^-11). At breastfeeding grouping level, positive association was found for MSDP and anxiety score in the breastfeeding group (0.07 SD change per SD change in MSDP, 95%CI, (0.06-0.09), P = 1.49 × 10^-20) and non-breastfeeding group (0.07 SD change per SD change in MSDP, 95%CI, (0.05-0.09), P = 7.19 × 10^-8). Compared with non-MSDP group, the protective effect (reflected by coefficients) of breastfeeding on anxiety in the MSDP decreased. Our preliminary study found MSDP may lower the protective effect of breastfeeding on the adult offspring anxiety, depression and neuroticism, providing useful recommendations for health care service via quitting smoking during pregnancy and encouraging prolonged breastfeeding.

Are E-cigarettes associated with postpartum return to smoking? Secondary analyses of a UK pregnancy longitudinal cohort

OBJECTIVES

Postpartum return to smoking (PPRS) is an important public health problem. E-cigarette (EC) use has increased in recent years, and in a contemporary UK pregnancy cohort, we investigated factors, including ECs use, associated with PPRS.

DESIGN

Secondary analyses of a longitudinal cohort survey with questionnaires at baseline (8-26 weeks' gestation), late pregnancy (34-36 weeks) and 3 months after delivery.

SETTING

17 hospitals in England and Scotland in 2017.

PARTICIPANTS

The cohort recruited 750 women who were current or recent ex-smokers and/or EC users. A subgroup of women reported being abstinent from smoking in late pregnancy (n=162, 21.6%), and of these 137 (84.6%) completed the postpartum questionnaire and were included in analyses.

OUTCOME MEASURES

Demographics, smoking behaviours and beliefs, views and experience of ECs and infant feeding.

RESULTS

35.8% (95% CI 28% to 44%) of women reported PPRS. EC use in pregnancy (adjusted OR 0.34, 95% CI 0.13 to 0.85) and breast feeding (adjusted OR 0.06, 95% CI 0.02 to 0.24) were inversely associated with PPRS, while household member smoking at 3 months post partum was positively associated with PPRS (adjusted OR 11.1, 95% CI 2.47 to 50.2).

CONCLUSION

EC use in pregnancy could influence PPRS. Further research is needed to confirm this and investigate whether ECs could be used to prevent PPRS.

A systematic review of mental health professionals, patients and carers' perceived barriers and enablers to supporting smoking cessation in mental health settings

Introduction

Evidence-based smoking cessation and temporary abstinence interventions to address smoking in mental health settings are available, but the impact of these interventions is limited.

Aims and Methods

We aimed to identify and synthesize the perceived barriers and enablers to supporting smoking cessation in mental health settings. Six databases were searched for articles reporting the investigation of perceived barriers and enablers to supporting smoking cessation in mental health settings. Data were extracted and coded using a mixed inductive/deductive method to the theoretical domains framework, key barriers and enablers were identified through the combining of coding frequency, elaboration, and expressed importance.

Results

Of 31 included articles, 56 barriers/enablers were reported from the perspectives of mental healthcare professionals (MHPs), 48 from patient perspectives, 21 from mixed perspectives, and 0 from relatives/carers. Barriers to supporting smoking cessation or temporary abstinence in mental health settings mainly fell within the domains: environmental context and resources (eg, MHPs lack of time); knowledge (eg, interactions around smoking that did occur were ill informed); social influences (eg, smoking norms within social network); and intentions (eg, MHPs lack positive intentions to deliver support). Enablers mainly fell within the domains: environmental context and resources (eg, use of appropriate support materials) and social influences (eg, pro-quitting social norms).

Conclusions

The importance of overcoming competing demands on staff time and resources, the inclusion of tailored, personalized support, the exploitation of patients wider social support networks, and enhancing knowledge and awareness around the benefits smoking cessation is highlighted.

Implications

Identified barriers and enablers represent targets for future interventions to improve the support of smoking cessation in mental health settings. Future research needs to examine the perceptions of the carers and family/friends of patients in relation to the smoking behavior change support delivered to patients.

Prenatal Tobacco Exposure and the Risk of Tobacco Smoking and Dependence in Offspring: a Systematic Review and Meta-Analysis

BACKGROUND

There is some compelling, though not comprehensive, epidemiological evidence which suggests an association between prenatal tobacco exposure and tobacco smoking/dependence in offspring. We conducted a systematic review and meta-analysis to identify the magnitude and consistency of associations reported between prenatal tobacco exposure and subsequent tobacco smoking/dependence in offspring.

METHODS

Using the PRISMA guideline, we systematically searched PubMed, SCOPUS, EMBASE and Psych-INFO to identify relevant studies. The methodological quality of all identified studies was checked by the Newcastle-Ottawa Scale. Inverse variance weighted random effects meta-analysis was used to estimate pooled risk ratio (RR) and 95 % confidence intervals (CI). We stratified outcomes by tobacco smoking initiation, lifetime tobacco smoking, current tobacco smoking and tobacco dependence. We further performed subgroup and leave-one-out sensitivity analyses. The protocol of this review was registered in the PROSPERO.

RESULTS

Twenty-six cohort and one case-control study were included in the final meta-analysis. We found elevated pooled risks of tobacco smoking initiation [RR = 2.08, (95 % CI: 1.18-3.68)], ever tobacco smoking [RR = 1.21, (95 % CI: 1.05-1.38)], current tobacco smoking [RR = 1.70, (95 % CI: 1.48-1.95)] and tobacco dependence [RR = 1.50, (95 % CI: 1.31-1.73)] in offspring exposed to maternal prenatal tobacco use compared to non-exposed. We also noted higher risk estimate of current tobacco smoking in offspring exposed to heavy prenatal tobacco smoking [RR = 1.68, (95 % CI: 1.26-2.23)] when compared to prenatal exposure to lighter tobacco use [RR = 1.39, (95 % CI: 1.09-1.78)]. There was no association observed between paternal smoking during pregnancy and tobacco smoking in offspring.

CONCLUSION

Offspring exposed to maternal prenatal tobacco smoking are at an increased risk of tobacco smoking/dependence, indicating that tobacco smoking cessation during gestation may be imperative to reduce these risks in offspring.

Estimating causal and time-varying effects of maternal smoking on youth smoking

INTRODUCTION

Maternal smoking is a well-known risk factor for youth smoking, yet whether this relationship is causal remains unresolved. This study utilizes propensity score methods for causal inference to robustly account for shared risk factors between maternal and offspring smoking.

METHODS

An 8-year longitudinal cohort of 900 adolescents in the Chicago area were followed starting from approximately age 15.6. The effects of maternal lifetime smoking (MLS) and prenatal tobacco exposure (PTE) (among participants reporting MLS) on offspring's past 30-day smoking, daily smoking status and smoking frequency were examined using logistic regression and Poisson regression after nearest-neighbor propensity matching. Age dependency of this relationship was then examined across the age range of 15-25 using time-varying effect modeling.

RESULTS

Propensity matching yielded 438 and 132 pairs for MLS and PTE study samples, respectively. MLS demonstrated significant associations with past 30-day smoking (RR 1.09; 95% CI 1.04-1.14), daily smoking (RR 1.08; 95% CI 1.05-1.12), and smoking frequency of offspring (RR 1.32; 95% CI 1.15-1.52), with stable effects across age. Among participants reporting MLS, having PTE showed significant additional effects on daily smoking (RR 1.09; 95% CI 1.02-1.17) and age-dependency that showed significance during young adulthood but not adolescence.

CONCLUSION

The relationship between maternal and offspring smoking was not fully accounted for by shared risk factors, suggesting possible causation with PTE having a delayed effect across age. Targeted prevention efforts should be made on maternal smoking-exposed adolescents to mitigate their risks of developing heavy smoking habits in adulthood.

Pre- and postnatal maternal smoking and offspring smoking trajectories: Evidence from a 20-year birth cohort

Maternal smoking is associated with increased risk of smoking in the offspring. However, it remains unclear whether this association depends on the timing of exposure to maternal smoking. We investigated the association between prenatal and/or postnatal maternal smoking and offspring smoking during adolescence. Participants (N = 1661) were from the Québec Longitudinal Study of Child Development cohort. We identified longitudinal trajectories of maternal smoking from before pregnancy to child age 12 years using group-based trajectory modeling (GBTM). Adolescent (12-19 years) smoking trajectories were also identified using GBTM. Associations between maternal smoking and offspring smoking trajectories were estimated using multinomial logistic regressions. We used propensity score inverse probability weighting (IPW) to account for the differential distribution of maternal and familial characteristics across exposure groups. We identified four distinct groups for maternal smoking: no (66.1%), decreasing (5.6%), increasing (9.5%) and persistent (18.8%) smoking, and three adolescent smoking trajectories: abstinent, early-onset (before age 15) and late-onset (after age 15). In IPW-adjusted models, youth with mothers with decreasing, increasing and persistent smoking had higher risk of being early-onset smokers compared with youth with mothers in the non-smoking group. We also found that only youth whose mothers were persistent smokers had an increased risk of late-onset smoking. Regardless of timing, offspring exposure to maternal smoking is associated with increased risk of smoking during adolescence. More research is needed on how to create effective smoking cessation campaigns that span preconception, prenatal, and postnatal periods to help prevent intergenerational transmission of smoking behaviors.

The effect of maternal smoking on offspring smoking is unrelated to heritable personality traits or initial subjective experiences

INTRODUCTION

Maternal smoking is a risk factor for offspring smoking. Lifetime maternal smoking vs. prenatal tobacco exposure (PTE) appear to act through different mechanisms. This study tested the hypothesis that maternal smoking measures' effects on offspring smoking could be attributable to hereditary mechanisms: personality traits (novelty-seeking, impulsivity, neuroticism, self-esteem) and initial subjective smoking experiences (pleasurable, unpleasurable, dizziness).

METHODS

Data were drawn from the Social and Emotional Contexts of Adolescent Smoking Patterns (SECASP) study, an 8-year longitudinal study of 9 th or 10 th graders at baseline (≈age 15) who experiment with smoking (<100 lifetime cigarettes; N=594) at baseline. Young adult smoking frequency at the 8-year follow-up (≈age 23) was examined as a function of baseline characteristics (heritable trait, maternal smoking, PTE, sex) and baseline smoking frequency and nicotine dependence. Structural equation models determined whether inclusion of each heritable trait among offspring confounded the effects of maternal smoking (PTE or maternal smoking) on offspring smoking and nicotine dependence.

RESULTS

Impulsiveness was associated with intermediate adolescent smoking frequency (B=0.135, SD=0.043 p=0.002) and nicotine dependence (B=0.012, SD=0.003, p<0.001). Unpleasurable first experience (B=0.886, SD=0.374, p=0.018) and dizziness (B=0.629, SD=0.293, p=0.032) showed a trend with intermediate smoking frequency that was non-significant after correcting for multiple comparisons. These traits did not confound maternal smoking's effects.

CONCLUSIONS

None of the heritable traits examined in this model explained the effect of maternal smoking measures on adolescence or young adulthood offspring smoking. Further research is needed to elucidate the mechanism by which PTE and maternal smoking are linked to offspring smoking.

Mendelian randomisation approaches to the study of prenatal exposures: A systematic review

BACKGROUND

Mendelian randomisation (MR) designs apply instrumental variable techniques using genetic variants to study causal effects. MR is increasingly used to evaluate the role of maternal exposures during pregnancy on offspring health.

OBJECTIVES

We review the application of MR to prenatal exposures and describe reporting of methodologic challenges in this area.

DATA SOURCES

We searched PubMed, EMBASE, Medline Ovid, Cochrane Central, Web of Science, and Google Scholar.

STUDY SELECTION AND DATA EXTRACTION

Eligible studies met the following criteria: (a) a maternal pregnancy exposure; (b) an outcome assessed in offspring of the pregnancy; and (c) a genetic variant or score proposed as an instrument or proxy for an exposure.

SYNTHESIS

We quantified the frequency of reporting of MR conditions stated, techniques used to examine assumption plausibility, and reported limitations.

RESULTS

Forty-three eligible studies were identified. When discussing challenges or limitations, the most common issues described were known potential biases in the broader MR literature, including population stratification (n = 29), weak instrument bias (n = 18), and certain types of pleiotropy (n = 30). Of 22 studies presenting point estimates for the effect of exposure, four defined their causal estimand. Twenty-four studies discussed issues unique to prenatal MR, including selection on pregnancy (n = 1) and pleiotropy via postnatal exposure (n = 10) or offspring genotype (n = 20).

CONCLUSIONS

Prenatal MR studies frequently discuss issues that affect all MR studies, but rarely discuss problems specific to the prenatal context, including selection on pregnancy and effects of postnatal exposure. Future prenatal MR studies should report and attempt to falsify their assumptions, with particular attention to issues specific to prenatal MR. Further research is needed to evaluate the impacts of biases unique to prenatal MR in practice.

Maternal prenatal thyroid function and trajectories of offspring emotional and behavioural problems: findings from the ALSPAC cohort

Maternal thyroid hormone may have impact on fetal brain development and consequently lead to offspring mental health problems. This study examined the role of maternal prenatal thyroid function on trajectories of offspring emotional and behavioural problems. Data were taken from the Avon Longitudinal Study of Parents and Children. A total of 4839 mother-child pairs were included. Thyroid-stimulating hormone (TSH) levels, free thyroxine (FT4), and thyroid peroxidase antibodies (TPO-Ab) were assessed during the first trimester of pregnancy. Childhood emotional and behavioural problems were assessed using the Strengths and difficulties questionnaire. A group-based modelling approach was used to identify the different trajectories of offspring emotional and behavioural problems reported by parents over four waves of measurement at age 3.5 (42 months), 6.75 (81 months), 9 and 11 years. Multinomial logistic regression was then used to test for an association between hormone levels and class membership. We identified four trajectories of offspring emotional and behavioural problems; normative-decreasing (49.7%), moderate-decreasing (35.7%), moderate-static (8.4%), and high-decreasing (6.2%) trajectory. There were no significant differences in the mean values of mother's FT4, TSH, and the proportion of mothers with positive TPO-Ab between trajectories. Univariable and multivariable multinomial logistic models showed no association between maternal thyroid function (FT4, TSH, and TPO-Ab) and the trajectories of offspring emotional and behavioural problems. The results of our study show that maternal thyroid parameters in a community population are not associated with trajectories of offspring emotional and behavioural problems.

The role of maternal prenatal thyroid function on offspring depression: Findings from the ALSPAC cohort

Maternal thyroid dysfunction during pregnancy may contribute to offspring neurobehavioral disorders. In this paper, we investigate the relationship between maternal thyroid function during pregnancy and offspring depression and anxiety. Data were taken from the Avon Longitudinal Study of Parents and Children. A total of 2,920 mother-child pairs were included. Thyroid-stimulating hormone levels, free thyroxine (FT4), and thyroid peroxidase antibodies were assessed during the first trimester of pregnancy because maternal supply is the only source of thyroid hormone for the fetus during the first 12 weeks of gestation. Child symptoms of depression and anxiety were assessed using the Development and Well-Being Assessment at ages 7.5 and 15 years. The odds of presenting with depression and anxiety were estimated using the generalized estimating equation. The level of FT4 during the first trimester of pregnancy was associated with child depression combined at ages 7.5 and 15 (odds ratio = 1.21, 95% confidence interval [1.00, 1.14]. An increase of 1 standard deviation of FT4 during pregnancy increased the odds of child depression by 28% after adjustment made for potential confounders. No association was found among maternal levels of thyroid-stimulating hormone, FT4, and thyroid peroxidase antibodies and childhood anxiety. In conclusion, increased levels of FT4 during the first trimester of pregnancy appear be linked to greater risk of offspring depression.

DNA methylation links prenatal smoking exposure to later life health outcomes in offspring

BACKGROUND

Maternal smoking during pregnancy is associated with adverse offspring health outcomes across their life course. We hypothesize that DNA methylation is a potential mediator of this relationship.

METHODS

We examined the association of prenatal maternal smoking with offspring blood DNA methylation in 2821 individuals (age 16 to 48 years) from five prospective birth cohort studies and perform Mendelian randomization and mediation analyses to assess whether methylation markers have causal effects on disease outcomes in the offspring.

RESULTS

We identify 69 differentially methylated CpGs in 36 genomic regions (P value < 1 × 10-7) associated with exposure to maternal smoking in adolescents and adults. Mendelian randomization analyses provided evidence for a causal role of four maternal smoking-related CpG sites on an increased risk of inflammatory bowel disease or schizophrenia. Further mediation analyses showed some evidence of cg25189904 in GNG12 gene mediating the effect of exposure to maternal smoking on schizophrenia-related outcomes.

CONCLUSIONS

DNA methylation may represent a biological mechanism through which maternal smoking is associated with increased risk of psychiatric morbidity in the exposed offspring.

Comparison of nicotine exposure during pregnancy when smoking and abstinent with nicotine replacement therapy: systematic review and meta-analysis

BACKGROUND AND AIMS

Smoking during pregnancy is strongly associated with negative pregnancy and perinatal outcomes. Some guidelines recommend nicotine replacement therapy (NRT) for smoking cessation during pregnancy, but adherence with NRT is generally poor and could be partially explained by nicotine-related safety concerns. We compared pregnant women's cotinine and nicotine exposures from smoking with those when they were abstinent from smoking and using NRT.

DESIGN

Systematic review with meta-analysis and narrative reporting. Twelve studies were included: in most, only one type of NRT was used. Seven were quality-assessed and judge of variable quality.

SETTING

Studies from any setting that reported nicotine or cotinine levels when smoking and later when abstinent and using NRT.

PARTICIPANTS

Pregnant women who smoked and became abstinent but used NRT either in a cessation study or in a study investigating other impacts of NRT.

MEASUREMENTS

We quality-assessed longitudinal cohort studies using a modified version of the Newcastle-Ottawa scale. For meta-analysis, we used mean within-person differences in cotinine or nicotine levels when smoking and at later follow-up when abstinent and using NRT. Where such data were not available, we calculated differences in group mean levels and reported these narratively, indicating where data were not completely longitudinal.

FINDINGS

Of the 12 included studies, four cotinine-measuring studies (n = 83) were combined in a random effects meta-analysis; the pooled estimate for the mean difference (95% confidence intervals) in cotinine levels between when women were smoking and abstinent but using NRT was 75.3 (57.1 to 93.4) ng/ml (I2  = 42.1%, P = 0.11). Of eight narratively-described studies, six reported lower cotinine and/or nicotine levels when abstinent and using NRT; two had mixed findings, with higher levels when abstinent but using NRT reported from at least one assay time-point.

CONCLUSIONS

Pregnant women who use nicotine replacement therapy instead of smoking reduce their nicotine exposure.

Toward an Intergenerational Model for Tobacco-Focused CBPR: Integrating Youth Perspectives via Photovoice

The growing prominence of community-based participatory research (CBPR) presents as an opportunity to improve tobacco-related intervention efforts. CBPR collaborations for tobacco/health, however, typically engage only adults, thus affording only a partial understanding of community context as related to tobacco. This is problematic given evidence around age of tobacco use initiation and the influence of local tobacco environments on youth. The CEASE and Resist youth photovoice project was developed as part of the Communities Engaged and Advocating for a Smoke-free Environment (CEASE) CBPR collaboration in Southwest Baltimore. With the broader CEASE initiative focused on adult smoking cessation, CEASE and Resist had three aims: (1) elucidate how youth from a high-tobacco-burden community perceive/interact with their local tobacco environment, (2) train youth as active change agents for tobacco-related community health, and (3) improve intergenerational understandings of tobacco use/impacts within the community. Fourteen youth were recruited from three schools and trained in participatory research and photography ethics/guiding principles. Youth met at regular intervals to discuss and narrate their photos. This article provides an overview of what their work revealed/achieved and discusses how including participatory youth research within traditionally adult-focused work can facilitate intergenerational CBPR for sustainable local action on tobacco and community health.

Maternal smoking during pregnancy and autism: using causal inference methods in a birth cohort study

An association between maternal smoking in pregnancy and autism may be biologically plausible, but the evidence to date is inconsistent. We aimed to investigate the causal relationship between maternal smoking during pregnancy and offspring autism using conventional analysis and causal inference methods. In the Avon Longitudinal Study of Parents and Children we investigated the association of maternal smoking during pregnancy (exposure) with offspring autism spectrum disorder (ASD) or possible ASD diagnosis (n = 11,946) and high scores on four autism-related traits (outcomes) (n = 7402-9152). Maternal smoking was self-reported and also measured using an epigenetic score (n = 866-964). Partner's smoking was used as a negative control for intrauterine exposure (n = 6616-10,995). Mendelian randomisation (n = 1002-2037) was carried out using a genetic variant at the CHRNA3 locus in maternal DNA as a proxy for heaviness of smoking. In observational analysis, we observed an association between smoking during pregnancy and impairments in social communication [OR = 1.56, 95% CI = 1.29, 1.87] and repetitive behaviours, but multivariable adjustment suggested evidence for confounding. There was weaker evidence of such association for the other traits or a diagnosis of autism. The magnitude of association for partner's smoking with impairments in social communication was similar [OR = 1.56, 95% CI = 1.30, 1.87] suggesting potential for shared confounding. There was weak evidence for an association of the epigenetic score or genetic variation at CHRNA3 with ASD or any of the autism-related traits. In conclusion, using several analytic methods, we did not find enough evidence to support a causal association between maternal smoking during pregnancy and offspring autism or related traits.

Maternal Prenatal Thyroid Function and Offspring ADHD: Findings From the ALSPAC Cohort

Thyroid hormone plays a pivotal role in the developing brain and may affect the development of attention deficit hyperactivity disorder (ADHD). This study aimed to examine the role of maternal thyroid function during pregnancy on offspring ADHD. A total of 2912 mother-child pairs were included from the Avon Longitudinal Study of Parents and Children. Thyroid parameters were assessed during the first trimester of pregnancy. Offspring ADHD was assessed using the Development and Well-Being Assessment at the ages of 7.5 and 15 years. The odds of presenting with ADHD were estimated using generalized estimating equations. Levels of thyroid-stimulating hormone (odds ratio [OR], 0.92; 95% confidence interval [CI], 0.48-1.75), free thyroxine (OR, 1.07; 95% CI, 0.87-1.32), and thyroid peroxidase antibodies (OR, 1.00; 95% CI, 0.80-1.25) were not associated with ADHD in children aged 7.5 and 15 years. This study showed no association between maternal thyroid function and offspring ADHD.

The role of nicotinic receptor genes (CHRN) in the pathways of prenatal tobacco exposure on smoking behavior among young adult light smokers

BACKGROUND

Prenatal tobacco exposure (PTE) is associated with more frequent smoking among young, light smokers. Little is known about how nicotinic acetylcholine receptor (CHRN) genes may contribute to this relationship.

METHODS

Data were drawn from a longitudinal cohort of young light smokers of European ancestry (N = 511). Three single nucleotide polymorphisms (SNPs) among offspring, rs16969968 and rs6495308 in CHRNA5A3B4 and rs2304297 in CHRNB3A6, were analyzed with respect to whether they 1) predict PTE status; 2) confound the previously-reported effects of PTE on future smoking; 3) have effects on youth smoking frequency that are mediated through PTE; and 4) have effects that are moderated by PTE.

RESULTS

rs2304297 and rs6495308 were associated with increased likelihood and severity of PTE, respectively. In a path analysis, rs16969968 directly predicted more frequent smoking in young adulthood (B = 1.50, p = .044); this association was independent of, and not mediated by, PTE. The risk of rs16969968 (IRR = 1.07, p = .015) and the protective effect of rs2304297 (IRR = 0.84, p < .001) on smoking frequency were not moderated by PTE. PTE moderated the effect of rs6495308, such that these alleles were protective against later smoking frequency only among non-exposed youth (IRR = 0.85, p < .001).

CONCLUSIONS

The association between offspring CHRNB3A6 and PTE is a novel finding. The risk of rs16969968 on youth smoking is independent and unrelated to that of PTE among young, light smokers. PTE moderates the protective effect of rs6495308 on youth smoking frequency. However, PTE's pathway to youth smoking behavior was not explained by these genetic factors, leaving its mechanism(s) of action unclear.

DNA methylation as a marker for prenatal smoke exposure in adults

Background

Prenatal smoke exposure is known to be robustly associated with DNA methylation among offspring in early life, but whether the association persists into adulthood is unclear. This study aimed to investigate the long-term effect of maternal smoke exposure on DNA methylation in 754 women (mean age 30 years); to replicate findings in the same women 18 years later and in a cohort of 230 men (mean age 53 years); and to assess the extent to which a methylation score could predict prenatal smoke exposure.

Methods

We first carried out an epigenome-wide association analysis for prenatal smoke exposure and performed replication analyses for the top CpG sites in the other samples. We derived a DNA methylation score based on previously identified CpG sites and generated receiver operating characteristic (ROC) curves to assess the performance of these scores as predictors of prenatal smoke exposure.

Results

We observed associations at 15 CpG sites in 11 gene regions: MYO1G, FRMD4A, CYP1A1, CNTNAP2, ARL4C, AHRR, TIFAB, MDM4, AX748264, DRD1, FTO (false discovery rate <5%). Most of these associations were specific to exposure during pregnancy, were present 18 years later and were replicated in a cohort of men. A DNA methylation score could predict prenatal smoke exposure (30 years previously) with an area under the curve of 0.72 (95% confidence interval 0.69, 0.76).

Conclusions

The results of this study provide robust evidence that maternal smoking in pregnancy is associated with changes in DNA methylation that persist in the exposed offspring for many years after prenatal exposure.

Improving Behavioral Support for Smoking Cessation in Pregnancy: What Are the Barriers to Stopping and Which Behavior Change Techniques Can Influence These? Application of Theoretical Domains Framework

Behavioral support interventions are used to help pregnant smokers stop; however, of those tested, few are proven effective. Systematic research developing effective pregnancy-specific behavior change techniques (BCTs) is ongoing. This paper reports contributory work identifying potentially-effective BCTs relative to known important barriers and facilitators (B&Fs) to smoking cessation in pregnancy; to detect priority areas for BCTs development. A Nominal Group Technique with cessation experts (n = 12) elicited an expert consensus on B&Fs most influencing women's smoking cessation and those most modifiable through behavioral support. Effective cessation interventions in randomized trials from a recent Cochrane review were coded into component BCTs using existing taxonomies. B&Fs were categorized using Theoretical Domains Framework (TDF) domains. Matrices, mapping BCT taxonomies against TDF domains, were consulted to investigate the extent to which BCTs in existing interventions target key B&Fs. Experts ranked "smoking a social norm" and "quitting not a priority" as most important barriers and "desire to protect baby" an important facilitator to quitting. From 14 trials, 23 potentially-effective BCTs were identified (e.g., information about consequences). Most B&Fs fell into "Social Influences", "Knowledge", "Emotions" and "Intentions" TDF domains; few potentially-effective BCTs mapped onto every TDF domain. B&Fs identified by experts as important to cessation, are not sufficiently targeted by BCT's currently within interventions for smoking cessation in pregnancy.

Factors associated with the effectiveness and reach of NHS stop smoking services for pregnant women in England

BACKGROUND

The UK National Health Service provides Stop Smoking Services for pregnant women (SSSP) but there is a lack of evidence concerning how these are best organised. This study investigates influences on services' effectiveness and also on their propensity to engage pregnant smokers with support in stopping smoking.

METHODS

Survey data collected from 121/141 (86%) of SSSP were augmented with data from Hospital Episode Statistics and the 2011 UK National Census. 'Reach' or propensity to engage smokers with support was defined as the percentage of pregnant smokers setting a quit date with SSSP support, and 'Effectiveness' as the percentage of women who set a quit date who also reported abstinence at four weeks later. A bivariate (i.e. two outcome variable) response Markov Chain Monte Carlo model was used to identify service-level factors associated with the Reach and Effectiveness of SSSP.

RESULTS

Beta coefficients represent a percentage change in Reach and Effectiveness by the covariate. Providing the majority of one-to-one contacts in a clinic rather than at home increased both Reach (%) (β: 6.97, 95% CI: 3.34, 10.60) and Effectiveness (%) (β: 7.37, 95% CI: 3.03, 11.70). Reach of SSSP was also increased when the population served was more deprived (β for increase in Reach with a one unit increase in IMD score: 0.55, 95% CI: 0.25, 0.85), had a lower proportion of people with dependent children (β: -2.52, 95% CI: -3.82, -1.22), and a lower proportion of people in managerial or professional occupations (β: -0.31, 95% CI: -0.59, -0.03). The Effectiveness of SSSP was decreased in those areas that had a greater percentage of people >16 years with no educational qualifications (β: -0.51, 95% CI: -0.95, -0.07).

CONCLUSIONS

To engage pregnant smokers and to encourage them to quit, it may be more efficient for SSSP support to be focussed around clinics, rather than women's homes. Reach of SSSP is inversely associated with disadvantage and efforts should be made to contact these women as they are less likely to achieve abstinence in the short and longer term.

The effect of prenatal smoking exposure on daily smoking among teenage offspring

AIMS

To study the predictive associations between maternal smoking and the impact of quitting smoking during pregnancy and offspring daily smoking at age 15-16 years.

DESIGN

The Northern Finland Birth Cohort 1986 (NFBC86) includes 99% of all births in the region and has an ongoing follow-up. Data were collected using questionnaires at 24th gestational week during pregnancy and after delivery, and at follow-up in 2001-02, when the offspring were aged 15-16 years.

SETTING

Northern Finland.

PARTICIPANTS

NFBC86 included 9432 live born children. Data regarding maternal smoking during pregnancy and offspring smoking at age 15-16 years were available for 4462 subjects (47.3% of the original sample).

MEASUREMENTS

The outcome was offspring's self-reported daily smoking. Maternal smoking during pregnancy was considered using a four-class variable: (1) no smoking, (2) mother had smoked, but had quit smoking before becoming pregnant, (3) mother quit smoking during the 1st trimester and (4) mother quit smoking after the 1st trimester or continued smoking throughout the pregnancy. Information regarding paternal smoking during pregnancy, maternal and paternal smoking and education level, family structure and dwelling at offspring's age 15-16 years were considered potential confounding variables.

FINDINGS

Continuing smoking after the 1st trimester increased the odds of daily smoking among offspring, independently of confounding factors [odds ratio (OR) = 1.8, 95% confidence interval (CI) = 1.3-2.5]. Continuing to smoke after the 1st trimester was associated with higher odds compared with quitting smoking during the 1st trimester. Also, parental smoking at offspring age 15-16 years increased the odds of offspring daily smoking, independently of prenatal smoking exposure.

CONCLUSIONS

Prenatal smoking exposure increases the risk for offspring adolescent daily smoking. Quitting smoking during the early stages of pregnancy may decrease the odds for offspring smoking.

A systematic review and narrative summary of family-based smoking cessation interventions to help adults quit smoking

BACKGROUND

Smoking is the most significant preventable cause of morbidity and early mortality in the world. The family is an influential context in which smoking behaviour occurs.

METHODS

A systematic review and narrative summary of family-based interventions to help adults quit smoking was conducted.

RESULTS

Eight controlled trials were included. Risk of bias was high. The smoking-related outcome of the intervention was self-reported smoking status/abstinence, validated by objective measures (including saliva thiocynate or breath carbon monoxide). Follow-up ranged from 6 weeks to 5 years. The main target groups were: pregnant women (1), pregnant women who smoked (2), men at risk of cardiovascular disease (2), adult smokers (1), parents who smoked (1) and couples who both smoked (1). Interventions included family members but most did not go further by drawing on family, systemic or relational theories to harness the influence of family on smoking behaviour. Only three studies directly compared the effects on smoking behaviour of a family-based (i.e., interventions that involve a member of the family) versus an individual-based (i.e., interventions that use behaviour change techniques that focus on the individual) intervention. None of these studies found significant differences between groups on the smoking behaviour of the main target group.

CONCLUSIONS

We have yet to develop family-based smoking cessation interventions that harness or re-direct the influence of family members on smoking behaviour in a positive way. Thus, it is likely that individualised-approaches to smoking cessation will prevail.

'Opt-out' referrals after identifying pregnant smokers using exhaled air carbon monoxide: impact on engagement with smoking cessation support

Background

In the UK, free smoking cessation support is available to pregnant women; only a minority accesses this. ‘Opt-out’ referrals to stop smoking services (SSS) are recommended by UK guidelines. These involve identifying pregnant smokers using exhaled carbon monoxide (CO) and referring them for support unless they object.

Methods

To assess the impact of ‘opt-out’ referrals for pregnant smokers on SSS uptake and effectiveness, we conducted a ‘before–after’ service development evaluation. In the 6-month ‘before’ period, there was a routine ‘opt-in’ referral system for self-reported smokers at antenatal ‘booking’ appointments. In the 6-month ‘after’ period, additional ‘opt-out’ referrals were introduced at the 12-week ultrasound appointments; women with CO≥4 ppm were referred to, and outcome data were collected from, local SSS.

Results

Approximately 2300 women attended antenatal care in each period. Before the implementation, 536 (23.4%) women reported smoking at ‘booking’ and 290 (12.7%) were referred to SSS. After the implementation, 524 (22.9%) women reported smoking at ‘booking’, an additional 156 smokers (6.8%) were identified via the ‘opt-out’ referrals and, in total, 421 (18.4%) were referred to SSS. Over twice as many women set a quit date with the SSS after ‘opt-out’ referrals were implemented (121 (5.3%, 95% CI 4.4% to 6.3%) compared to 57 (2.5%, 95% CI 1.9% to 3.2%) before implementation) and reported being abstinent 4 weeks later (93 (4.1%, 95% CI 3.3% to 4.9%) compared to 46 (2.0%, 1.5% to 2.7%) before implementation).

Conclusions

In a hospital with an ‘opt-in’ referral system, adding CO screening with ‘opt-out’ referrals as women attended ultrasound examinations doubled the numbers of pregnant smokers setting quit dates and reporting smoking cessation.

Geographic Variation in Maternal Smoking during Pregnancy in the Missouri Adolescent Female Twin Study (MOAFTS)

Objective

Despite well-known adverse health effects of maternal smoking during pregnancy (MSP), it is still unclear if MSP varies geographically and if neighborhood socioeconomic deprivation (SED) plays an important role in MSP. This study aims to investigate small-area geographic variation in MSP and examine the association of SED with MSP.

Methods

The Missouri Adolescent Female Twin Study (MOAFTS) is a cohort study of female like-sex twins born in Missouri to Missouri-resident parents during 1975–1985. Biological mothers completed a baseline interview in 1995–1998 and reported MSP with the twins. Residential address of the mother at birth was geocoded. We developed a census tract-level SED index using a common factor approach based on 21 area-level socioeconomic variables from the 1980 Census data. Multilevel logistic regressions estimated geographic heterogeneity (random effect) in MSP and the odds ratios (ORs, fixed effects) of neighborhood SED associated with MSP.

Results

Of 1658 MOAFTS mothers, 35.2% reported any MSP and 21.9% reported MSP beyond the first trimester. Neighborhood SED was associated with any MSP (the highest vs. the lowest quartile: OR = 1.90, 95% confidence interval [CI] = 1.40–2.57, P_trend<0.001) and MSP beyond the first trimester (OR = 1.98, 95% CI = 1.38–2.85, P_trend = 0.002) in unadjusted analyses. After adjusting for individual covariates (demographics, socioeconomic conditions, alcohol use, and parents’ cohabitation), neighborhood SED was not associated with MSP, but geographic variation still persisted in MSP (variance = 0.41, P = 0.003) and in MSP beyond the first trimester (variance = 0.82, P<0.001).

Conclusions

Neighborhood SED was associated with MSP in unadjusted analyses but this association could be explained by individual socioeconomic conditions. Nonetheless, significant geographic variation in MSP persisted and was not accounted for by differences in neighborhood SED. To develop effective interventions to reduce MSP, further studies are necessary to explore underlying reasons for its geographic variation.

Elevated risk of nicotine dependence among sib-pairs discordant for maternal smoking during pregnancy: evidence from a 40-year longitudinal study

BACKGROUND

Compelling evidence links maternal smoking during pregnancy with elevated risk of nicotine dependence among the offspring. However, no study to date has examined the maternal smoking during pregnancy-nicotine dependence link among sibling-pairs discordant for maternal smoking during pregnancy. We tested two hypotheses that, if supported, suggest that the maternal smoking during pregnancy-nicotine dependence link may be physiologically mediated.

METHODS

Study participants were adult offspring of women enrolled in the Providence and Boston sites of the Collaborative Perinatal Project (1959-1966). Approximately 10% of these adult offspring (average age: 39.6 years) were enrolled in the New England Family Study (n = 1,783), a follow-up study that oversampled families with multiple siblings. Logistic regression models predicting maternal smoking during pregnancy risk on various prospectively collected smoking and marijuana use outcomes, including nicotine dependence, were fit using models that allowed between-mother effects of maternal smoking during pregnancy exposure to differ from within-mother effects. In the absence of significant effect heterogeneity, we calculated a combined estimate.

RESULTS

Maternal smoking during pregnancy predicted progression from weekly smoking to nicotine dependence (odds ratio = 1.4 [95% confidence interval = 1.2, 1.8]), but not weekly smoking or progression to marijuana dependence.

CONCLUSIONS

Current evidence from sibling-pairs discordant for maternal smoking during pregnancy is consistent with previous reports of a dose-response association between maternal smoking during pregnancy and nicotine dependence, as well as of up-regulation of nicotine receptors among animals exposed to maternal smoking during pregnancy. Together, they provide support for the existence of a physiologically mediated link between maternal smoking during pregnancy and nicotine dependence.

Is grand-parental smoking associated with adolescent obesity? A three-generational study

BACKGROUND/OBJECTIVES

Data from previous studies consistently suggest that maternal smoking is positively associated with obesity later in life. Whether this association persists across generations is unknown. We examined whether grand-parental smoking was positively associated with overweight status in adolescence.

SUBJECT/METHODS

Participants were grandmother-mother-child triads in the Nurses' Health Study II (NHS II), the Nurses Mothers' Cohort Study and the Growing up Today Study (GUTS). Grandmothers provided information on their and their partner's smoking during pregnancy with the child's mother. Information on child's weight and height at ages 12 (N=3094) and 17 (N=3433) was obtained from annual or biennial GUTS questionnaires. We used logistic regression to estimate the odds ratios (ORs) of being overweight or obese, relative to normal weight.

RESULTS

Grand-maternal smoking during pregnancy was not associated with overweight status in adolescence. After adjusting for covariates, the OR of being overweight or obese relative to normal weight at age 12 years in girls whose grandmothers smoked 15+ cigarettes daily during pregnancy was 1.21 (95% confidence interval (CI) 0.74-1.98; P(trend)=0.31) and 1.07 (0.65-1.77; P(trend)=0.41) in boys. Grand-paternal smoking during pregnancy was associated with being overweight or obese at age 12 in girls only, but not at age 17 for either sex: the OR for being overweight or obese at age 12 was 1.38 (95% CI 1.01-1.89; P(trend)=0.03) in girls and 1.31 (95% CI 0.97-1.76; P(trend)=0.07) in boys. Among children of non-smoking mothers, the OR for granddaughter obesity for grand-paternal smoking was attenuated and no longer significant (OR 1.28 (95% CI 0.87-1.89; P(trend)=0.18)).

CONCLUSIONS

Our findings suggest that the association between maternal smoking and offspring obesity may not persist beyond the first generation. However, grand-paternal smoking may affect the overweight status of the granddaughter, likely through the association between grand-paternal smoking and maternal smoking.

Prenatal exposure to maternal smoking and offspring DNA methylation across the lifecourse: findings from the Avon Longitudinal Study of Parents and Children (ALSPAC)

Maternal smoking during pregnancy has been found to influence newborn DNA methylation in genes involved in fundamental developmental processes. It is pertinent to understand the degree to which the offspring methylome is sensitive to the intensity and duration of prenatal smoking. An investigation of the persistence of offspring methylation associated with maternal smoking and the relative roles of the intrauterine and postnatal environment is also warranted. In the Avon Longitudinal Study of Parents and Children, we investigated associations between prenatal exposure to maternal smoking and offspring DNA methylation at multiple time points in approximately 800 mother–offspring pairs. In cord blood, methylation at 15 CpG sites in seven gene regions (AHRR, MYO1G, GFI1, CYP1A1, CNTNAP2, KLF13 and ATP9A) was associated with maternal smoking, and a dose-dependent response was observed in relation to smoking duration and intensity. Longitudinal analysis of blood DNA methylation in serial samples at birth, age 7 and 17 years demonstrated that some CpG sites showed reversibility of methylation (GFI1, KLF13 and ATP9A), whereas others showed persistently perturbed patterns (AHRR, MYO1G, CYP1A1 and CNTNAP2). Of those showing persistence, we explored the effect of postnatal smoke exposure and found that the major contribution to altered methylation was attributed to a critical window of in utero exposure. A comparison of paternal and maternal smoking and offspring methylation showed consistently stronger maternal associations, providing further evidence for causal intrauterine mechanisms. These findings emphasize the sensitivity of the methylome to maternal smoking during early development and the long-term impact of such exposure.

Partner smoking and maternal cotinine during pregnancy: implications for negative control methods

BACKGROUND

Comparison of the associations of maternal and mother's partner smoking with offspring outcomes is, in theory, a useful method for assessing whether there may be an intrauterine effect of tobacco exposure on these outcomes. However, this approach assumes that the effects of passive smoking from exposure to partner smoking during pregnancy are minimal. We evaluated this assumption using a biochemical measure of tobacco exposure in pregnant women.

METHODS

Cotinine levels taken during the first trimester of pregnancy were measured in a sample of 3928 women from the Avon Longitudinal Study of Parents and Children. Median cotinine values were compared across categories of smoking heaviness (cigarettes per day) of the women during the first trimester and in non-smoking women by the smoking heaviness of their partner.

RESULTS

Cotinine levels were substantially higher in women who smoked compared to non-smokers (range of medians across smoking heaviness categories: 900-5362 ng/ml versus 20 ng/ml, interquartile range (IQR) (0-63) for non-smokers). In contrast, cotinine levels in non-smoking women were only very weakly related to partner smoking status (range of medians in women with smoking partners: 34-69 ng/ml versus 12 ng/ml, IQR (0-48) in women with non-smoking partners).

CONCLUSIONS

Levels of tobacco exposure from partner smoking, as assessed by cotinine, were low in non-smoking pregnant women. This suggests that using mother's partner's smoking as a negative control for investigating intrauterine effects is valid.