Early environmental quality and life-course mental health effects: The Equal-Life project.

BACKGROUND: There is increasing evidence that a complex interplay of factors within environments in which children grows up, contributes to children's suboptimal mental health and cognitive development. The concept of the life-course exposome helps to study the impact of the physical and social environment, including social inequities, on cognitive development and mental health over time. METHODS: Equal-Life develops and tests combined exposures and their effects on children's mental health and cognitive development. Data from eight birth-cohorts and three school studies (N = 240.000) linked to exposure data, will provide insights and policy guidance into aspects of physical and social exposures hitherto untapped, at different scale levels and timeframes, while accounting for social inequities. Reasoning from the outcome point of view, relevant stakeholders participate in the formulation and validation of research questions, and in the formulation of environmental hazards. Exposure assessment combines GIS-based environmental indicators with omics approaches and new data sources, forming the early-life exposome. Statistical tools integrate data at different spatial and temporal granularity and combine exploratory machine learning models with hypothesis-driven causal modeling. CONCLUSIONS: Equal-Life contributes to the development and utilization of the exposome concept by (1) integrating the internal, physical and social exposomes, (2) studying a distinct set of life-course effects on a child's development and mental health (3) characterizing the child's environment at different developmental stages and in different activity spaces, (4) looking at supportive environments for child development, rather than merely pollutants, and (5) combining physical, social indicators with novel effect markers and using new data sources describing child activity patterns and environments.

Growth patterns from birth to overweight at age 5-6 years of children with various backgrounds in socioeconomic status and country of origin: the ABCD study.

INTRODUCTION: Children from minority groups are at increased risk of overweight. This study compared BMI growth patterns from birth onwards of boys and girls with overweight at 5-6 years, according to socioeconomic status (SES) and country of origin, in order to gain more insight into the critical periods of growth to overweight. METHODS: A total of 3714 singletons of the multi-ethnic ABCD study were included. Within children with overweight at age 5-6 years (N = 487, prevalence boys: 11.6%, girls: 14.6%), BMI growth patterns from birth onwards (12.8 serial measurements; SD = 3.1) were compared between children from European (69.4%) and non-European mothers (30.6%), and between children from low (20.8%), mid (37.0%) or high SES (42.2%), based on maternal educational level. RESULTS: BMI growth to overweight did not differ between children of European or non-European mothers, but it did differ according to maternal SES. Children with overweight in the low and mid SES group had a lower BMI in the first 2 years of life, an earlier adiposity rebound and increased in BMI more rapidly after age 2, resulting in a higher BMI at age 7 years compared to children with overweight in the high SES group [∆BMI (kg/m2 ) between high and low SES: boys 1.43(95%CI:0.16;3.01) and girls 1.91(0.55;3.27)]. CONCLUSION: Children with overweight from low SES have an early adiposity rebound and accelerated growth to a higher BMI at age 5-6 years compared to children with overweight from the high SES group. These results imply that timing of critical periods for overweight development is earlier in children with a low socioeconomic background as compared to other children.

Shedding Some Light in the Dark-A Comparison of Personal Measurements with Satellite-Based Estimates of Exposure to Light at Night among Children in the Netherlands.

BACKGROUND: Exposure to light at night (LAN) can perturb the biological clock and affect sleep and health. Previous epidemiological studies have evaluated LAN levels measured by satellites, but the validity of this measure as a proxy for personal LAN exposure is unclear. In addition, outdoor satellite-measured LAN levels are higher in urban environments, which means that this measure could potentially represent a proxy for other, likely urban, environmental exposures. OBJECTIVES: We evaluated correlations of satellite-assessed LAN with measured bedroom light levels and explored correlations with other environmental exposures, in particular, air pollution, green space, and area-level socioeconomic position (SEP). METHODS: We compared satellite measurements with evening and nighttime bedroom measurements of illuminance (in units of lux) for 256 children, and we evaluated correlations between satellite-based measures and other urban exposures such as air pollution, area-level SEP, and surrounding green space for 3,021 children. RESULTS: Satellite-measured LAN levels (nanowatts per centimeter squared per steradian) were not correlated with measured evening or nighttime lux levels [Spearman correlation coefficients ([Formula: see text]) [Formula: see text] to 0.04]. There was a weak correlation with measurements during the darkest time period if parents and their children reported that outdoor light sometimes or usually influenced indoor light levels ([Formula: see text], [Formula: see text]). In contrast, satellite-measured LAN levels were correlated with air pollution ([Formula: see text] with [Formula: see text], [Formula: see text] with [Formula: see text]), and surrounding green space ([Formula: see text] for green space within [Formula: see text] of the home). A weak correlation with area-level SEP was also observed ([Formula: see text]). CONCLUSIONS: Outdoor satellite-assessed outdoor LAN exposure levels were correlated with urban environmental exposures, but they were not a good proxy for indoor evening or nighttime personal exposure as measured in our study population of 12-y-old children. Studies planning to evaluate potential risks from LAN should consider such modifying factors as curtains and indoor lighting and the use of electronic devices and should include performing indoor or personal measurements to validate any exposure proxies. The moderate-to-strong correlation of outdoor LAN with other environmental exposures should be accounted for in epidemiological investigations. https://doi.org/10.1289/EHP3431.

Socioeconomic inequalities in psychosocial problems of children: mediating role of maternal depressive symptoms.

Background: Socioeconomically disadvantaged children often have psychosocial problems. This study examined the mediating role of maternal depressive symptoms during pregnancy, infancy and early childhood in the association between maternal education, as indicator of socioeconomic status (SES), and child's psychosocial problems. Methods: Included were 3410 children from the Amsterdam Born Children and their Development (ABCD) study. To assess the child's psychosocial problems at age 5-6 years, mothers and teachers completed the Strengths and Difficulties Questionnaire (SDQ). Maternal depressive symptoms were assessed using the Center for Epidemiologic Studies Depression Scale and the Depressive Anxiety and Stress Scale 21. Mediation analysis was performed to calculate the direct effect of maternal education on SDQ score and indirect effects through maternal depressive symptoms. Results: The mean mother-reported SDQ total score was significantly higher (P < 0.001) for children of low-educated mothers (6.74 ± 4.41) compared with children of highly educated mothers (4.47 ± 3.73). Levels of maternal depressive symptoms were also higher in low-educated mothers during pregnancy, infancy and early childhood. Maternal depressive symptoms explained 27.5% of the association between maternal education and mother-reported SDQ scores and 22.9% for combined mother/teacher SDQ scores. Maternal depressive symptoms during pregnancy had the strongest indirect effect. Conclusion: Maternal depressive symptoms during pregnancy mediate the association between low maternal education and child's psychosocial problems. Early recognition and treatment of maternal depressive symptoms is important to prevent psychosocial problems in children, especially in those with low education.

Determinants of cortisol during pregnancy - The ABCD cohort.

BACKGROUND: Psychosocial stress during pregnancy has been proposed as a major contributor of glucocorticoid-mediated programming of the fetal hypothalamic-pituitary adrenal (HPA) axis, with later adverse health consequences. However, evidence linking maternal stress to maternal cortisol values during pregnancy is inconclusive. A possible explanation for this is that other maternal factors overshadow any potential effects of stress on cortisol levels. We studied a large cohort of pregnant women with extensive data on pregnancy characteristics to determine the respective contributions of biological, environmental and psychosocial stress factors to cortisol levels in pregnancy. METHODS: We used data from 3039 women from the Amsterdam Born Children and their Development-study cohort. Serum cortisol was measured in blood, collected at the first prenatal visit, at different gestational ages (median=91days, range=40-256days), and at various time points during the day (median=11:45h, range=08:00-18:30h). We assessed associations between maternal serum cortisol in pregnancy and biological factors, lifestyle factors and stress factors, including depression, anxiety, pregnancy-related anxiety, work stress, parenting stress and fatigue. RESULTS: In multivariable analysis, variables that were associated with higher cortisol levels in pregnancy were lower maternal age [1.5nmol/l, 95%CI (0.6-2.4)], being nulliparous [21.5 nmol/l (15.9-27.1)], lower pre-pregnancy body mass index (BMI) [1.3nmol/l (0.3-2.4)], higher C-reactive protein (CRP) [1.0nmol/l (0.4-1.5)], carrying a female fetus [9.2nmol/l (1.8-16.5)], non-smoking [14.2nmol/l (0.6-27.7)], sufficient sleep [8.5nmol/l (0.9-16.1)], and being unemployed [12.7nmol/l (2.2-23.2)]. None of the psychosocial stressors was significantly associated with serum cortisol levels in pregnancy. A total of 32% of all variance in cortisol was explained by gestational age, maternal age, time of day, parity, pre-pregnancy BMI, CRP, fetal sex, smoking behavior, self-reported sleep sufficiency, and employment. CONCLUSIONS: Our data suggest that maternal cortisol during pregnancy is mainly affected by biological and lifestyle factors, but not by psychosocial factors. We suggest that psychosocial stress in pregnancy might program the fetus through other mechanisms than through altering maternal cortisol levels.

Inclusion of migrants and ethnic minorities in European birth cohort studies-a scoping review.

BACKGROUND: Migrant and ethnic minority groups constitute substantial parts of European populations. They frequently experience health disadvantages relative to the respective majority populations. Birth cohort studies can help to disentangle social and biological factors producing these health inequalities over the life course. We investigated whether birth cohorts in European countries (i) assess migration history and ethnicity in the study design; and (ii) use this information in data analyses. METHODS: A scoping review was performed in which European birth cohort studies were identified using dedicated web-based registries, MEDLINE and EMBASE. Two reviewers systematically assessed all identified birth cohorts and selected those fulfilling defined inclusion criteria (e.g. enrolment after 1980). Publications and websites were screened for information on the inclusion of migrants and ethnic minorities. To obtain more detailed information, researchers of enrolled birth cohorts were contacted individually. RESULTS: Eighty-eight birth cohorts were identified in 20 European countries, with more than 486 250 children enrolled in total. Sixty-two studies (70.5%) reported collecting data about migration history or ethnic background. Twenty-three studies (26%) used information on migration history or ethnicity for data analyses or plan to do so in future. CONCLUSION: The majority of European birth cohorts assessed participants' migration history or ethnic background; however, this information was seldom used for comparative analyses in trying to disentangle reasons for health inequalities. Also, heterogeneous indicators were used. Better use of data already available, as well as harmonization of data collection on migration history and ethnicity, could yield interesting insights into the production of health inequalities.

Effect of socioeconomic status on psychosocial problems in 5- to 6-year-old preterm- and term-born children: the ABCD study.

This study aimed at analysing the association between socioeconomic status (SES) and psychosocial problems in preterm- and term-born children. Scores of mothers and teachers on the Strengths and Difficulties Questionnaire (SDQ) regarding 217 preterm-born children (<37 weeks' gestation, mean 34 weeks) were compared with 4336 term-born children in the Amsterdam Born Children and their Development (ABCD) cohort at age 5-6 years. Associations between SDQ scores and SES (maternal education and perceived income adequacy) were examined with multivariate linear regression analysis. The mean mother-reported total difficulties score was significantly higher for preterm children (6.1 ± 4.7) than for term children (5.2 ± 4.1). After covariate adjustment, this difference was 0.5 (95 % CI 0.0-1.0). For preterm children 16.1 % of the mothers reported psychosocial problems compared with 10.1 % for term children. Lower maternal education and lower income adequacy were significantly related to higher SDQ scores of mothers and teachers. Differences in mothers' SDQ score between preterm and term children were larger in the high-education (Δ0.9, 95 % CI 0.2-1.5) and high-income group (Δ0.9, 95 % CI 0.3-1.6). No significant differences were found between preterm and term children in the SDQ scores reported by teachers. Low level of maternal education and inadequate income showed a much stronger association with psychosocial problems than preterm birth. No combined effect of low SES and preterm birth was found. This study corroborates the evidence for the strength of the disadvantageous effects of low SES on early psychosocial development.

Exploring educational disparities in risk of preterm delivery: a comparative study of 12 European birth cohorts.

BACKGROUND: An association between education and preterm delivery has been observed in populations across Europe, but differences in methodology limit comparability. We performed a direct cross-cohort comparison of educational disparities in preterm delivery based on individual-level birth cohort data. METHODS: The study included data from 12 European cohorts from Denmark, England, France, Lithuania, the Netherlands, Norway, Italy, Portugal, and Spain. The cohorts included between 2434 and 99 655 pregnancies. The association between maternal education and preterm delivery (22-36 completed weeks of gestation) was reported as risk ratios, risk differences, and slope indexes of inequality with 95% confidence intervals (CIs). RESULTS: Singleton preterm live delivery proportion varied between 3.7% and 7.5%. There were large variations between the cohorts in the distribution of education and maternal characteristics. Nevertheless, there were similar educational differences in risk of preterm delivery in 8 of the 12 cohorts with slope index of inequality varying between 2.2 [95% CI 1.1, 3.3] and 4.0 [95% CI 1.4, 6.6] excess preterm deliveries per 100 singleton deliveries among the educationally most disadvantaged, and risk ratio between the lowest and highest education category varying from 1.4 [95% CI 1.1, 1.8] to 1.9 [95% CI 1.2, 3.1]. No associations were found in the last four cohorts. CONCLUSIONS: Educational disparities in preterm delivery were found all over Europe. Despite differences in the distributions of education and preterm delivery, the results were remarkably similar across the cohorts. For those few cohorts that did not follow the pattern, study and country characteristics did not explain the differences.

[Preterm birth and low socioeconomic status: more psychosocial problems at age 5-6?]. / Prematuur geboren en lage sociaal-economische status: meer psychosociale problemen op 5- en 6-jarige leeftijd?

OBJECTIVE: Comparison of the association between socioeconomic status (SES) and psychosocial problems in preterm-born and term-born children. DESIGN: Cohort study (Amsterdam Born Children and their Development (ABCD) cohort). METHOD: For 217 preterm-born children (mean gestation 34 weeks), Strengths and Difficulties Questionnaire (SDQ) scores were compared with 4336 term-born children at age 5-6 years. Associations between SDQ scores and SES (maternal education and perceived income adequacy) were examined with multivariate linear regression analysis. RESULTS: Mothers of preterm-born children often had a lower level of education. The mean SDQ total score was significantly higher for preterm-born children (6.1; SD: 4.7) than for term-born children (5.2; SD: 4.1). No significant differences were found between preterm-born and term-born children in the SDQ scores reported by teachers. For preterm-born children, 16.1% of the mothers reported psychosocial problems compared with 10.1% for term-born children. Lower maternal education and lower income adequacy were significantly related to higher SDQ scores. Differences in SDQ score between preterm-born and term-born children were most pronounced in the group with highly educated mothers (Δ0.9; 95%-CI: 0.2-1.5) and high income (Δ0.9; 95%-CI: 0.3-1.6). CONCLUSION: There was no additional effect of preterm birth on psychosocial problems in children with a low level of maternal education or inadequate income. This study corroborates earlier evidence regarding the disadvantageous effects of low SES on psychosocial development.

[Ethnic differences in uptake of professional maternity care assistance]. / Etnische verschillen in het gebruik van kraamzorg.

OBJECTIVE: To examine the ethnic differences in the uptake of professional maternity care assistance (MCA) in the Netherlands, and the factors that may explain these differences. Additionally the effect of MCA on health risk behaviour around infants is examined. DESIGN: Questionnaire survey. METHOD: Questionnaire data from 3967 mothers from the ABCD study (Amsterdam Born Children and their Development) included during pregnancy in 2003-2004, were used. We examined the explanatory role of ethnicity, age, socioeconomic status, mastery of the Dutch language, parity, housing situation and place of giving birth on MCA uptake, and the effect of MCA uptake on health risk behaviour around infants, such as smoking indoors, infant sleep behaviour, infant nutrition, and response to infant crying. RESULTS: Mothers of non-Western origin less often used MCA than Dutch mothers (Ghanaian: 70%; Turkish: 75%; Moroccan: 79%; Surinamese: 81%; Dutch Caribbean: 85% vs. Dutch: 95%). Higher educational level, better mastery of the Dutch language, having a paid job and home delivery were all independently associated with the uptake of MCA, and also partially explained ethnic differences in the uptake of MCA. Mothers who received MCA more often breastfed, more often gave vitamin K when not breastfeeding, and more often lived in smoke-free homes. The protective effect of MCA was stronger for non-Western mothers than for Dutch mothers. CONCLUSION: Mothers of non-Western origin make less use of professional MCA. Given that the use of MCA is associated with a less risk behaviour around infants, efforts should be made to improve the accessibility of professional MCA for mothers of non-Western origin.

Low maternal education is associated with increased growth velocity in the first year of life and in early childhood: the ABCD study.

UNLABELLED: The objective of this study is first to examine the relation of maternal education and growth velocity during the first year of life and early childhood (1-5 years). The second objective is to determine the potential explanatory role of standardized birth weight, maternal smoking during pregnancy, maternal prepregnancy body mass index (BMI), and infant feeding practice in this relation. We used longitudinal growth data of 1,684 participants with Dutch ethnicity participating in a population-based cohort study (Amsterdam Born Children and their Development study). Growth velocity of weight and of weight-for-length were calculated by subtracting the weight and weight-for-length standard deviation scores (SDS), respectively of two time periods. In the first year of life, children with low-educated mothers had an increase in SDS of 0.26 (95 % confidence interval (CI) 0.08-0.45) for weight compared to children with high-educated mothers. In early childhood, children with low-educated mothers had a 0.27 SDS (95 % CI 0.11-0.42) increase for weight-for-length, compared to children with high-educated mothers. Using path analysis, these inequalities could partly be explained by maternal smoking, duration of breastfeeding, maternal age, and maternal BMI. CONCLUSION: Children with low-educated mothers had an increased weight gain during the first year of life and an increased weight-for-length gain in early childhood compared to children with high-educated mothers. Although underlying mechanisms were not completely clarified, an optimal duration of breastfeeding, cessation of maternal smoking, and reduction of maternal BMI seem to reduce these educational inequalities in early growth and possible adverse consequences of accelerated growth.

Smoking overrules many other risk factors for small for gestational age birth in less educated mothers.

BACKGROUND: Although there is convincing evidence for the association between small for gestational age (SGA) and socioeconomic status (SES), it is not known to what extent explanatory factors contribute to this association. AIM: To examine to what extent risk factors could explain educational inequalities in SGA. STUDY DESIGN: In this study fully completed data were available for 3793 pregnant women of Dutch origin from a population-based cohort (ABCD study). Path-analysis was conducted to examine the role of explanatory factors in the relation of maternal education to SGA. RESULTS: Low-educated pregnant women had a higher risk of SGA offspring compared to the high-educated women (OR 1.98, 95% CI 1.35-2.89). In path-analysis, maternal cigarette smoking and maternal height explained this association. Maternal age, hypertension, chronic disease, late entry into antenatal care, neighborhood income, underweight, environmental cigarette smoking, drug abuse, alcohol use, caffeine intake, fish intake, folic acid intake, anxiety, and depressive symptoms did not play a role in the association between maternal education and SGA birth. CONCLUSION: Among a large array of potential factors, the elevated risk of SGA birth among low-educated women appeared largely attributable to maternal smoking and to a lesser extent to maternal height. To reduce educational inequalities more effort is required to include low-educated women especially in prenatal intervention programs such as smoking cessation programs instead of effort into reducing other SGA-risk factors, though these factors might still be relevant at the individual level.

Explaining socioeconomic inequalities in childhood blood pressure and prehypertension: the ABCD study.

Much remains to be understood about the socioeconomic inequalities in hypertension that continue to exist. We investigated the association of socioeconomic status with blood pressure and prehypertension in childhood. In a prospective cohort, 3024 five- to six-year-old children had blood pressure measurements and available information on potential explanatory factors, namely birth weight, gestational age, smoking during pregnancy, pregnancy-induced hypertension, familial hypertension, maternal body mass index, breastfeeding duration, domestic tobacco exposure, and body mass index. The systolic and diastolic blood pressures of children from mid-educated women were 1.0-mm Hg higher (95% CI, 0.4-1.7) and 0.9-mm Hg higher (95% CI, 0.3-1.4), and the blood pressures of children with low-educated women were 2.2-mm Hg higher (95% CI, 1.4-3.0) and 1.7-mm Hg higher (95% CI, 1.1-2.4) compared with children with high-educated women. Children with mid- (odds ratio, 1.50; 95% CI, 1.18-1.92) or low-educated mothers (odds ratio, 1.80; 95% CI, 1.35-2.42) were more likely to have prehypertension compared with children with high-educated mothers. Using path analyses, birth weight, breastfeeding duration, and body mass index were determined as having a role in the association of maternal education with offspring blood pressure and prehypertension. The socioeconomic gradient in hypertension appears to emerge from childhood as the results show a higher blood pressure and more prehypertension in children from lower socioeconomic status families. Socioeconomic disparities could be reduced by improving 3 factors in particular, namely birth weight, breastfeeding duration, and body mass index, but other factors might also play a role.

Association between body size and blood pressure in children from different ethnic origins.

OBJECTIVE: To assess associations between body size and blood pressure in children (5-6 years) from different ethnic origins. METHOD: Five ethnic groups of the ABCD cohort were examined: Dutch (n=1 923), Turkish (n=99), Moroccan (n=187), Black-African (n=67) and Black-Caribbean (n=121). Data on body-mass-index (BMI), waist-to-height ratio (WHtR), fat-mass-index (FMI), and systolic blood pressure (SBP) and diastolic blood pressure (DBP), were collected. Linear regression analysis with restricted cubic splines was used to examine non-linear associations between body size and blood pressure, adjusted for age, sex, height and birth weight. RESULTS: Ethnic differences were found in associations of BMI with SBP and DBP (SBP: p=0.001 and DBP: p=0.01) and FMI with SBP (p=0.03). BMI and FMI had a relatively large positive association with SBP in Turkish children (BMI: ß=2.46mmHg; 95%CI:1.20-3.72; FMI: ß=2.41mmHg; 95%CI:1.09-3.73) compared to Dutch (BMI: ß=1.31mmHg; 95%CI:0.71-1.92; FMI: ß=0.84mmHg; 95%CI:0.23-1.45). Black-Caribbean and Moroccan children showed high blood pressure with low BMI and FMI. Moroccan children showed higher SBP with high BMI and FMI. WHtR was positively associated with SBP and DBP, similar in all ethnic groups. Generally, strongest associations with blood pressure were found for BMI in all ethnic groups. CONCLUSION: Ethnic-specific associations between BMI, and FMI and blood pressure are present at young age, with Turkish children showing the highest increase in blood pressure with increasing body size. The higher blood pressure in the Black-Caribbean and Moroccan children with low BMI needs further research. WHtR or FMI do not seem to be associated more strongly to blood pressure than BMI in any ethnic group.

Socioeconomic inequalities in lipid and glucose metabolism in early childhood in a population-based cohort: the ABCD-Study.

BACKGROUND: Socioeconomic inequalities in cardiovascular disease are pervasive, yet much remains to be understood about how they originate. The objective of this study was to explore the relations of socioeconomic status to lipid and glucose metabolism as indicators of cardiovascular health in 5-6 year olds. Additionally to explore the explanatory role of maternal factors, birth outcome, and child factors. METHODS: In 1308 5-6 year old ethnic Dutch children from the ABCD cohort study, lipids (cholesterol, LDL, HDL, triglycerides), glucose and C-peptide were measured after an overnight-fast. RESULTS: There were no differences in cholesterol, HDL, LDL, and triglycerides between socioeconomic groups, as indicated by maternal education and income adequacy. However, children of low educated mothers had on average a higher glucose (ß = 0.15; 95% confidence interval (CI) 0.03 - 0.27), logC-peptide (ß = 0.07; 95% CI 0.04 - 0.09), and calculated insulin resistance (HOMA-IR) (ß = 0.15; 95% CI 0.08 - 0.22) compared to children of high educated mothers. Only childhood BMI partly explained these differences (models controlled for age, height, and sex). CONCLUSIONS: The socioeconomic gradient in cardiovascular risk factors seems to emerge in early childhood. In absence of underlying mechanisms these empirical findings are relevant for public health care and further explanatory research.

Educational inequalities in perinatal outcomes: the mediating effect of smoking and environmental tobacco exposure.

OBJECTIVE: Socioeconomic status (SES) is adversely associated with perinatal outcomes. This association is likely to be mediated by tobacco exposure. However, previous studies were limited to single perinatal outcomes and devoted no attention to environmental tobacco exposure. Therefore, this study aimed firstly to explain the role of maternal smoking in the association between maternal education and preterm birth (PTB), low birth weight (LBW) and small for gestational age (SGA), and secondly to explain whether environmental tobacco smoke mediates these associations further. STUDY DESIGN: This study was nested in a population-based cohort study in the Netherlands, the Amsterdam Born Children and their Development (ABCD) study. Analyses were done in a sample of 3821 pregnant women of Dutch origin, using logistic regression analysis. RESULTS: Least educated women, who were more often smoking and exposed to environmental tobacco smoke, had a significantly higher risk of PTB (OR 1.95 [95% CI: 1.19-3.20]), LBW (OR 2.41 [95% CI: 1.36-4.27]) and SGA (OR 1.90 [95% CI 1.32-2.74]) than highly educated women. The mediating effect of smoking in the least educated women was 43% for PTB, 55% for LBW and 66% for SGA. Environmental tobacco smoke did not explain these associations further. After adjustment for maternal smoking, the association between lower maternal education and pregnancy outcomes was no longer significant. CONCLUSIONS: Smoking explains to a considerable extent the association between lower maternal education and adverse perinatal outcomes. Therefore, tobacco-interventions in lower educated women should be primarily focussed on maternal smoking to reduce PTB, LBW, and SGA. Additional attention to environmental tobacco exposure does not seem to reduce educational inequalities in perinatal outcomes.