Socioeconomic position, family context, and child cognitive development.

Socioeconomic position (SEP) may have different effects on cognitive development and family context could play a role in this association. This work aimed to analyse the role of socioeconomic positions, measured via various indicators collected longitudinally, in cognitive development at 7-11 years of age, evaluating the role of family context as a potential mediator. The study sample included 394 and 382 children from the INMA Gipuzkoa and Valencia cohorts, respectively. SEP indicators were assessed during pregnancy (family social class, parental education, employment, and disposable income) and at 7 (Gipuzkoa) and 11 (Valencia) years of age (At Risk of Poverty or Social Exclusion (AROPE)). Family context and cognitive development were measured with the Haezi-Etxadi Family Assessment Scale 7-11 (HEFAS 7-11) and Raven's Coloured Progressive Matrices (Raven's CPM), respectively. Linear regression models were developed to assess the relationships between (a) SEP-family context, (b) SEP-cognitive development, and (c) family context-cognitive development, adjusting for a priori-selected confounders. Simple and multiple mediation analyses were performed to explore the role of family context in the SEP-cognitive development relationship. Lower SEP was related with a lower cognitive score, this association being particularly robust for family social class. SEP indicators were related to subscales of family context, in particular those regarding cognitive stimulation, parental stress, and parenting. A relationship was also found between these three subscales and child cognitive development, mediating the effect of family social class on child cognition by 5.2, 5.5, and 10.8%, respectively, and 12.0% jointly.    Conclusion: Both family SEP and context contribute to a child's cognitive development. Equalising policies and positive parenting programmes could contribute to improving cognitive development in children. What is Known: • Parental social class, education, and employment status have been widely employed to measure socioeconomic position. What is New: • This work focuses on standard measurements of socioeconomic position but also other economic indicators such as the EHII and AROPE, and their effect on child cognitive development and family context. • Promotion of cognitive and linguistic development, parental stress and conflict, and parental profile fostering child development mediated the effect of family social class on cognitive development.

Exploration of thyroglobulin as a biomarker of iodine status in iodine-sufficient and mildly iodine-deficient pregnant women.

PURPOSE: Urinary iodine-to-creatinine ratio (UI/Creat) reflects recent iodine intake but has limitations for assessing habitual intake. Thyroglobulin (Tg) concentration, which increases with thyroid size, appears to be an indicator of longer-term iodine status in children and adults, however, less is known in pregnancy. This study investigated the determinants of serum-Tg in pregnancy and its use as an iodine-status biomarker in settings of iodine-sufficiency and mild-to-moderate deficiency. METHODS: Stored blood samples and existing data from pregnant women from the Netherlands-based Generation R (iodine-sufficient) and the Spain-based INMA (mildly-to-moderately iodine-deficient) cohorts were used. Serum-Tg and iodine status (as spot-urine UI/Creat) were measured at median 13 gestational weeks. Using regression models, maternal socio-demographics, diet and iodine-supplement use were investigated as determinants of serum-Tg, as well as the association between UI/Creat and serum-Tg. RESULTS: Median serum-Tg was 11.1 ng/ml in Generation R (n = 3548) and 11.5 ng/ml in INMA (n = 1168). When using 150 µg/g threshold for iodine deficiency, serum-Tg was higher in women with UI/Creat < 150 vs ≥ 150 µg/g (Generation R, 12.0 vs 10.4 ng/ml, P = 0.010; INMA, 12.8 vs 10.4 ng/ml, P < 0.001); after confounder adjustment, serum-Tg was still higher when UI/Creat < 150 µg/g (regression coefficients: Generation R, B = 0.111, P = 0.050; INMA, B = 0.157, P = 0.010). Iodine-supplement use and milk intake were negatively associated with serum-Tg, whereas smoking was positively associated. CONCLUSION: The association between iodine status and serum-Tg was stronger in the iodine-deficient cohort, than in the iodine-sufficient cohort. Serum-Tg might be a complementary (to UI/Creat) biomarker of iodine status in pregnancy but further evidence is needed.

Sleep problems at ages 8-9 and ADHD symptoms at ages 10-11: evidence in three cohorts from INMA study.

Sleep problems and attention deficit hyperactivity disorder (ADHD) are interrelated during childhood and preadolescence. The objective of this work is assessing if sleep problems at ages 8-9 represent an alarm sign for presenting ADHD problems at ages 10-11 in three cohorts from INMA Study. Participants were 1244 children from Gipuzkoa, Sabadell, and Valencia cohorts. Sleep problems were assessed (ages 8-9) with the sleep items of the Child's Behaviour Checklist (CBCL), and ADHD problems were collected through the Conner's Parent Rating Scales-Revised: Short Form (CPRS-R:S) (age 10-11). Minimally and fully adjusted negative binomial models were fitted for each CPRS-R:S scale. Linearity of the relationship was assessed with generalized additive models (cubic smoothing splines with 2, 3, and 4 knots). For sensitivity analyses, children with previous symptoms, those born preterm and small for gestational age, and cases with extreme values, were excluded. Sleep problems presented IRR (95% CI) of 1.14 (1.10-1.19), 1.20 (1.14-1.26), 1.18 (1.11-1.25), and 1.18 (1.13-1.23) for opposition, inattention, hyperactivity, and ADHD scales, respectively. Fully adjusted models slightly decreased the IRR, but the association remained similar and significant. Sensitivity analyses showed similar results to fully adjusted models with only hyperactivity shown a slight decrease on significance (p = 0.051) when ADHD cases at age 9 were excluded.   Conclusion: Sleep problems are an alarm sign for later neurodevelopment problems such as ADHD. Healthcare systems could take advantage implementing policies to pay special attention on the sleep habits and sleep hygiene. This could contribute to add evidence to public health programmes such as the Healthy Child Programme.

Poverty, social exclusion, and mental health: the role of the family context in children aged 7-11 years INMA mother-and-child cohort study.

Mental health problems are common in childhood and tend to be more frequent in populations at risk of poverty or social exclusion (AROPE). The family environment can play a role in reducing the impact of economic hardship on these problems. The aim of this study was to assess the effect of multidimensional poverty on the mental health of children aged 7-11 years and the role of the family environment in two areas of Spain. Participants were 395 and 382 children aged 7 and 11 from Gipuzkoa and Valencia, respectively. Internalizing and externalizing problem scales of the child behaviour checklist (CBCL) were used. AROPE indicators were obtained by questionnaire, and three dimensions of the family context (Organization of the Physical Environment and Social Context, Parental Stress and Conflict, and Parental Profile Fostering Development) were measured through subscales 3, 4 and 5 of the Haezi-Etxadi family assessment scale (7-11) (HEFAS 7-11), respectively. Data were analysed using negative binomial regression and Structural Equation Modelling. AROPE prevalence was 7.1 and 34.5% in Gipuzkoa and Valencia, respectively. In both cohorts, there was a significant increase in internalizing and externalizing problems among participants with a higher AROPE score. However, AROPE did not affect internalizing problems in children from families living in a better physical environment and with social support (Subscale 3). The AROPE effect was jointly mediated by subscales 4 and 5 in 42 and 62% of internalizing and externalizing problems, respectively. Preventing economic inequities by economic compensation policies, improving the neighbourhood and immediate environment around the school, and promoting positive parenting programmes can improve mental health in childhood.

Maternal occupational exposure to chemicals and child cognitive function.

BACKGROUND: Limited data exist regarding child neurodevelopment in relation to maternal occupational exposure to endocrine-disrupting chemicals (EDCs). METHODS: We included 1058 mother-child pairs from the INfancia y Medio Ambiente (INMA) project (2003-2008). Using a job-exposure matrix, exposure probability scores for ten EDC groups were assigned to each mother based on her longest held job during pregnancy. At the child's 5-year visit, the McCarthy Scales of Children's Abilities was administered, yielding the general cognitive index and scales for specific cognitive domains. We analyzed region-specific associations between EDC exposures and each outcome separately using adjusted linear regression and combined region-specific effect estimates using random-effects meta-analyses. RESULTS: Approximately 24% of women were exposed to at least one EDC group, but exposure to most individual EDC groups was low (<5%). Maternal organic solvent exposure was associated with lower quantitative scores among children (-5.8 points, 95% confidence interval: -11.0, -0.5). Though statistically non-significant, exposures to polycyclic aromatic hydrocarbons, phthalates, alkylphenolic compounds, and miscellaneous chemicals were associated with poorer offspring performance for most or all cognitive domains. CONCLUSIONS: This study found limited evidence for a role of maternal occupational EDC exposures on child cognition. Further research is needed to better characterize exposures among pregnant workers. IMPACT: Using data from a prospective birth cohort, we help fill an important research gap regarding the potential consequences of work-related exposure to endocrine-disrupting chemicals (EDCs) among pregnant women on child neurodevelopment. We expand on existing literature-largely limited to pesticide and organic solvent exposures-by using a job-exposure matrix to estimate exposure to several EDC groups. We found limited evidence of an association between maternal occupational EDC exposure and children's overall cognition. We did observe specific associations between exposure to organic solvents and lower quantitative reasoning scores.

Postnatal exposure to mercury and neuropsychological development among preschooler children.

The objective of this study was to describe the postnatal exposure to Hg and to evaluate its association with neuropsychological development among preschool children. The study population are 4-5 years old children (n = 1252) participant in the Spanish INMA Project. Total Hg was measured in cord blood and in hair samples taken at 4 years of age (2008-2012). Neuropsychological development was assessed using the McCarthy Scales of Children's Abilities (MSCA). Information on covariates and possible confounders was obtained by questionnaires during pregnancy and childhood. Generalized additive and linear regression models were built in order to assess the relationship between MSCA scores and Hg exposure. We also evaluated the magnitude of the possible bias generated from measurement error in seafood intake estimate from questionnaire and Hg determination. The geometric mean of hair Hg was 0.98 µg/g [95% confidence interval (CI) 0.94, 1.03]. In the regression analysis, the association between Hg and the MSCA scores was positive for all the scales and statistically significant for the verbal (ß = 0.89; 95%CI 0.38, 1.39), memory (ß = 0.42; 95%CI 0.09, 0.76) and general cognitive scales (ß = 1.35; 95%CI 0.45, 2.25). However, these associations were clearly attenuated when we adjusted by the children's fish intake variables or when took into account theoretical scenarios of low precision in fish intake and Hg measurements. Hg levels in this Spanish population were high in comparison with other European countries; however, we did not observe adverse effects on child neuropsychological development associated with this postnatal exposure to Hg.

Prenatal Omega-6:Omega-3 Ratio and Attention Deficit and Hyperactivity Disorder Symptoms.

OBJECTIVE: To evaluate whether higher omega-6:omega-3 (n-6:n-3) long-chain polyunsaturated fatty acid ratio in cord plasma is associated with more symptoms of attention deficit and hyperactivity disorder (ADHD) at 4 and 7 years of age. STUDY DESIGN: This study was based on a population-based birth cohort in Spain. N-6 arachidonic acid and n-3 eicosapentaenoic and docosahexaenoic acid concentrations were measured in cord plasma. At 4 years old, ADHD symptoms were reported by teachers through the ADHD Diagnostic and Statistical Manual of Mental Disorders, 4th ed checklist (n = 580). At 7 years old, ADHD symptoms were reported by parents through the Conners' Rating Scale-Revised (short form; n = 642). The ADHD variable was treated as continuous (score) and as dichotomous (symptom diagnostic criteria). Child and family general characteristics were prospectively collected through questionnaires. We applied pooled zero-inflated negative binomial and logistic regressions adjusted for covariates. RESULTS: A higher omega-6:omega-3 long-chain polyunsaturated fatty acid ratio in cord plasma was associated with a higher ADHD index (incidence rate ratio, 1.13; 95% CI, 1.03, 1.23) at 7 years old. The association was not observed at 4 years old (incidence rate ratio, 1.04; 95% CI, 0.92-1.18). No associations were found using ADHD symptom diagnostic criteria. CONCLUSIONS: High prenatal omega-6:omega-3 long-chain polyunsaturated fatty acid ratio preceded the appearance of subclinical ADHD symptoms during mid-childhood. Our findings suggest that maternal diet during pregnancy may modulate the risk to develop long-term ADHD symptoms in the offspring.

High doses of folic acid in the periconceptional period and risk of low weight for gestational age at birth in a population based cohort study.

PURPOSE: We investigated the association between maternal use of folic acid (FA) during pregnancy and child anthropometric measures at birth. METHODS: We included 2302 mother-child pairs from a population-based birth cohort in Spain (INMA Project). FA dosages at first and third trimester of pregnancy were assessed using a specific battery questionnaire and were categorized in non-user, < 1000, 1000-4999, and ≥ 5000 µg/day. Anthropometric measures at birth (weight in grams, length and head circumference in centimetres) were obtained from medical records. Small for gestational age according to weight (SGA-w), length (SGA-l) and head circumference (SGA-hc) were defined using the 10th percentile based on Spanish standardized growth reference charts. Multiple linear and logistic regression analyses were used to explore the association between FA dosages in different stages of pregnancy and child anthropometric measures at birth. RESULTS: In the multiple linear regression analysis, we found a tendency for a negative association between the use of high dosages of FA (≥ 5000 µg/day) in the periconceptional period of pregnancy and weight at birth compared to mothers who were non-users of FA (ß = - 73.83; 95% CI - 151.71, 4.06). In the multiple logistic regression, a greater risk of SGA-w was also evident among children whose mothers took FA dosages of 1000-4999 (OR = 2.21; 95% CI 1.17, 4.19) and of ≥ 5000 µg/day (OR = 2.32; 95% CI 1.06, 5.08) compared to mothers non-users of FA in the periconceptional period of pregnancy. CONCLUSION: Our findings suggest that a high dosage of FA (≥ 1000 µg/day) may be associated with an increased risk of SGA-w at birth.

Poor mothers, unhealthy children: the transmission of health inequalities in the INMA study, Spain.

BACKGROUND: The health of pregnant women and their fetuses are especially sensitive to socioeconomic conditions. This study analyzes the impact of maternal socioeconomic status (SES), evaluated by occupation and maternal education level, in preterm births (PTBs) and in small for gestational age (SGA) fetuses, considering the effect of the potential mediating factors on the SES and birth outcomes. METHODS: A total of 2497 mother/newborn dyads from the INMA-Spain project were studied. We examined maternal occupation and education in relation to PTB and SGA along with covariate data, using logistic regression analysis. Adjusted models for each of the outcome variables in relation to SES indicators were estimated, considering potential mediating factors. RESULTS: About 4.7% of babies were PTB and 9.7% SGA. Full adjusted logistic regression models showed similar odds ratio (OR) for SGA in both SES indicators. Manual working women or without university studies had higher risk of SGA than their counterpart groups (OR = 1.39% CI = 1.03-1.88 and OR = 1.39% CI = 1.00-2.00, respectively). Likewise, mothers with a manual occupation were at more risk of PTB than those with a non-manual occupation (OR = 1.74 95% CI = 1.13-2.74), but there was no association between education and PTB. Smoking, pre-pregnancy BMI and underweight gain during pregnancy were significantly associated to SGA births. The mother's age, presence of complications and overweight gain during pregnancy were related to PTB. CONCLUSION: The mother's socioeconomic disadvantage was consistently associated with birth outcomes giving rise to intergenerational transmission of health inequalities. Reducing inequalities requires eliminating the upstream causes of poverty itself.

Comparison of urinary iodine levels in women of childbearing age during and after pregnancy.

PURPOSE: Median urinary iodine concentration (UIC) is used to describe the iodine status of a population. However, the link between UIC and iodine intake may vary during pregnancy. The aim of this study was to compare UIC during and after pregnancy, adjusting for factors that affect iodine intake. METHODS: Two repeated measures of UIC and data on maternal iodine intake estimated through questionnaires were collected during pregnancy and 1-4 years after pregnancy in a subsample of women (n = 598) from a mother and child cohort study in Spain. Random-effects interval regression was used to assess the changes in UIC according to pregnancy status. RESULTS: Median UIC was similar during (133 µg/L) and after pregnancy (139 µg/L). After adjusting for iodised salt, iodine supplement consumption, and socio-demographic related variables, UIC was 24.0% (95% CI 11.3, 38.2) higher after than during pregnancy. This difference was maintained in a subsample of women with exhaustive information on diet (n = 291): 26.2%, 95% CI 10.3, 44.4. CONCLUSIONS: In an iodine sufficient area for the general population, iodine excretion was lower during than after pregnancy when factors affecting iodine intake were controlled for. Current recommendations of median UIC during pregnancy are based on the equivalence between iodine intake and UIC estimated from studies in non-pregnant populations, which might lead to overestimation of iodine deficiency during gestation. Further studies should evaluate the equivalence between iodine intake and its urinary excretion during pregnancy.

Prenatal exposure to mercury and longitudinally assessed fetal growth: Relation and effect modifiers.

BACKGROUND: Prenatal mercury exposure has been related to reductions in anthropometry at birth. Levels of mercury have been reported as being relatively elevated in the Spanish population. OBJECTIVE: To investigate the relation between prenatal exposure to mercury and fetal growth. METHODS: Study subjects were pregnant women and their newborns (n:1867) participating in a population-based birth cohort study set up in four Spanish regions from the INMA Project. Biparietal diameter (BPD), femur length (FL), abdominal circumference (AC), and estimated fetal weight (EFW) were measured by ultrasounds at 12, 20, and 34 weeks of gestation. Size at and growth between these points were assessed by standard deviation (SD) scores adjusted for constitutional characteristics. Total mercury (T-Hg) was determined in cord blood. Associations were investigated by linear regression models, adjusted by sociodemographic, environmental, nutritional - including four seafood groups - and lifestyle-related variables in each sub-cohort. Final estimates were obtained using meta-analysis. Effect modification by sex, seafood intake and polychlorinated biphenyl (PCB) congener 153 concentration was assessed. RESULTS: Geometric mean of cord blood T-Hg was 8.2µg/L. All the estimates of the association between prenatal Hg and growth from 0 to 12 weeks showed reductions in SD-scores, which were only statistically significant for BPD. A doubling of cord blood T-Hg was associated with a 0.58% reduction in size of BPD at week 12 (95% confidence interval -CI-: - 1.10, - 0.07). Size at week 34 showed estimates suggestive of a small reduction in EFW, i.e., a doubling of T-Hg levels was associated with a reduction of 0.38% (95% CI: - 0.91, 0.15). An interaction between PCB153 and T-Hg was found, with statistically significant negative associations of T-Hg with AC and EFW in late pregnancy among participants with PCB153 below the median. CONCLUSIONS: Exposure to mercury during pregnancy was associated with early reductions in BPD. Moreover, an antagonism with PCB 153 was observed with noteworthy reductions late in pregnancy in AC and EFW in the group with lower PCB153.

Maternal selenium status and neuropsychological development in Spanish preschool children.

BACKGROUND: The relationship between maternal selenium (Se) status and child neurodevelopment has been scarcely assessed. In a previous study we observed an inverse U-shaped association between maternal Se concentrations and infant neurodevelopment at 12 months of age. In this study, this non-linear association was explored at preschool age. The effect modification by breastfeeding, child's sex and cord blood mercury was also evaluated. METHODS: Study subjects were 490 mother-child pairs from the Spanish Childhood and Environment Project (INMA, 2003-2012). Child neuropsychological development was assessed at around 5 years of age by the McCarthy Scales of Children's Abilities (MSCA). Sociodemographic and dietary characteristics were collected by questionnaire at the first and third trimester of gestation and at 5 years of age. Se was measured in serum samples by ICP-MS at the end of the first trimester of pregnancy (mean ±â€¯standard deviation (SD) = 12.4 ±â€¯0.6 weeks of gestation). RESULTS: The mean ±â€¯SD of maternal serum Se concentrations was 79.9 ±â€¯8.1 µg/L. In multivariate analysis, no linear association was found between Se concentrations and the nine MSCA scales. Generalized additive models indicated inverted U-shaped relationships between Se concentrations and the verbal and global memory scales. When assessing the influence of effect modifiers, breastfeeding played a role: the association between Se and neuropsychological development was inverted U-shaped for the quantitative, general cognitive, working memory, fine motor, global motor and executive function scales only for non-breastfed children. CONCLUSION: Low and high maternal Se concentrations seem to be harmful for child neuropsychological development, however further studies should explore this non-linear relationship.

Maternal pre-pregnancy obesity and neuropsychological development in pre-school children: a prospective cohort study.

BackgroundMaternal pre-pregnancy obesity may impair infant neuropsychological development, but it is unclear whether intrauterine or confounding factors drive this association.MethodsWe assessed whether maternal pre-pregnancy obesity was associated with neuropsychological development in 1,827 Spanish children. At 5 years, cognitive and psychomotor development was assessed using McCarthy Scales of Children's Abilities, attention deficit hyperactivity disorder (ADHD) symptoms using the Criteria of Diagnostic and Statistical Manual of Mental Disorders, and autism spectrum disorder symptoms using the Childhood Asperger Syndrome Test. Models were adjusted for sociodemographic factors and maternal intelligence quotient. We used paternal obesity as negative control exposure as it involves the same source of confounding than maternal obesity.ResultsThe percentage of obese mothers and fathers was 8% and 12%, respectively. In unadjusted models, children of obese mothers had lower scores than children of normal weight mothers in all McCarthy subscales. After adjustment, only the verbal subscale remained statistically significantly reduced (ß: -2.8; 95% confidence interval: -5.3, -0.2). No associations were observed among obese fathers. Maternal and paternal obesity were associated with an increase in ADHD-related symptoms. Parental obesity was not associated with autism symptoms.ConclusionMaternal pre-pregnancy obesity was associated with a reduction in offspring verbal scores at pre-school age.

Association between breastfeeding duration and cognitive development, autistic traits and ADHD symptoms: a multicenter study in Spain.

BACKGROUND: Several studies have related longer breastfeeding duration to better intellectual performance in children. By contrast, few studies have investigated the potential protective effects of breastfeeding against behavioral problems such as attention deficit hyperactivity disorder (ADHD) symptoms, and even fewer on autism spectrum disorders (ASD) traits. METHODS: We examined the association between breastfeeding duration and cognitive development, attention, ADHD symptoms, and autistic traits using data from the INMA Project, a Spanish multicenter birth-cohort study, and taking into account the intensity of breastfeeding. Duration of any, predominant, and exclusive breastfeeding was documented during infancy through maternal questionnaires. Children (N = 1,346; mean age = 4.9 y) were assessed using the McCarthy Scales of Children's Abilities, Conners' Kiddie Continuous Performance Test, criteria of the DSM-ADHD symptoms form list, and the Childhood Autism Spectrum Test. RESULTS: After adjustment for several confounders, longer duration of breastfeeding was independently associated with better cognitive development and with fewer autistic traits. CONCLUSION: This study provides further evidence of a positive association of breastfeeding with cognitive function apart from socio-environmental factors, and also suggests a protective role against autistic traits. Results are in agreement with recommendations for prolonged breastfeeding duration to promote child development.

Distributions and determinants of urinary biomarkers of organophosphate pesticide exposure in a prospective Spanish birth cohort study.

BACKGROUND: Prenatal exposure to organophosphate pesticides (OPs) has been associated with impaired child development. Pesticide exposure determinants need to be studied in order to identify sources and pathways of pesticide exposure. The aim of this paper is to describe prenatal exposure to OPs and evaluate the associated factors in pregnant women. METHODS: The study population consisted of pregnant women (n = 573) who participated in the INMA birth cohort study in Valencia (Spain, 2003-2006). OP metabolites were analyzed in maternal urine at the 32nd week of gestation using a liquid chromatography-high resolution mass spectrometry method. The analysis included non-specific (diethyl phosphate [DEP], diethyl thiophosphate [DETP], dimethyl thiophosphate [DMTP], dimethyl dithiophosphate [DMDTP]) and specific metabolites (2-diethylamino-6-methyl-4-pyrimidinol [DEAMPY], 2-isopropyl-4-methyl-6-hydroxypyrimidine [IMPY], para-nitrophenol [PNP], and 3,5,6-trichloro-2-pyridinol [TCPY]). Information about the sociodemographic, environmental, and dietary characteristics was obtained by questionnaire. The association between log-transformed OPs and covariates was analyzed using multivariable interval censored regression. RESULTS: The detection frequencies were low, DMTP and TCPY being the most frequently detected metabolites (53.8% and 39.1%, respectively). All the OP metabolites were positively associated with maternal intake of fruits and vegetables. Other maternal characteristics related to the OPs were body mass index (BMI) before pregnancy and smoking habit during pregnancy. Women with lower BMI and those who did not smoke presented higher OP concentrations. Moreover, mothers who had a yard or garden with plants at home or who lived in an urban area were also more exposed to OPs. CONCLUSIONS: The OP detection frequencies and the concentrations observed in our study population were low, compared with most of the previously published studies. Given the high vulnerability of the fetus to neurotoxicant exposure, further research on the determinants of the body burden of OPs during pregnancy would be necessary. The knowledge gained from such studies would enhance the effectiveness of public health control and future recommendations in order to reduce the risk to both the health of pregnant women and the health and development of their children.

Prenatal mercury exposure and birth outcomes.

BACKGROUND: Results regarding the association between mercury exposure and anthropometry at birth, gestational length and placental weight are inconsistent, as is the role of seafood intake in these associations. OBJECTIVE: We assessed whether prenatal mercury exposure is associated with anthropometry at birth, placental weight and gestational length in a population with a relatively high exposure to mercury from seafood consumption. METHODS: Total mercury (T-Hg) was determined in cord blood from 1869 newborns with birth outcome measures, within the Spanish multicenter INMA cohort from 2004 to 2008. We adjusted cohort specific linear and Cox regression models to evaluate the association between T-Hg and birth anthropometry (weight, length, and head circumference), placental weight and gestational length. Non-spontaneous labor was taken to be censoring in the survival analysis. Final estimates were obtained using meta-analysis. RESULTS: Geometric mean T-Hg was 8.2µg/L. A doubling of T-Hg was associated with a 7.7g decrease in placental weight (95% CI: -13.6, -1.8) and marginally with head circumference (beta: -0.052cm, 95% CI: -0.109, 0.005). T-Hg was also inversely related to weight and length, although with weaker estimates. Mercury exposure was not associated with the length of gestation. The inverse relation between T-Hg and growth was enhanced when the intake of different seafood groups was adjusted for in the models. CONCLUSIONS: Prenatal mercury exposure may be associated with reduced placental and fetal growth. Confounding by fish intake should be considered when assessing these relationships.

Second-hand smoke exposure in 4-year-old children in Spain: Sources, associated factors and urinary cotinine.

INTRODUCTION: Second-hand smoke exposure (SHS) in children remains as a major pollution problem, with important consequences for children's health. This study aimed to identify the sources of exposure to SHS among 4-year-old children, comparing self-reports to a urinary biomarker of exposure, and characterize the most important variables related to SHS exposure in this population. METHODS: 4-year-old children's exposure to SHS was assessed by a parental-reported questionnaire and by urinary cotinine (UC) measurements in 1757 participants from 4 different areas of the Spanish INMA (INfancia y Medio Ambiente - Environment and Childhood) Project. The questionnaire about SHS included information about smoking habits at home by household members, and about exposure to SHS in other places including other homes, bars, restaurants or transportation. The association between quantified UC levels (>4ng/ml) and sociodemographic variables and the different sources of SHS exposure was examined using logistic regression. RESULTS: Based on parental reports, 21.6% of the children were exposed to SHS at home and 47.1% elsewhere; making a total 55.9% of the children exposed to SHS. In addition, 28.2% of the children whose parents reported being not regularly exposed to SHS had quantified UC values. Children from younger mothers (<34 vs. ≥39.4 y) had a higher odds of exposure to SHS [OR (95% CI): 2.28 (1.70-3.05) per year], as well as from families with a lower educational level [OR secondary: 2.12 (1.69-2.65); primary or less: 2.91 (2.19-3.88)]. The odds of quantifiable UC in children dropped after the smoking ban in public places [OR=0.59 (0.42-0.83)]. Regarding the sources of SHS exposure we observed that quantifiable UC odds was increased in children whose parents smoked at home in their presence [OR mother occasionally: 13.39 (7.03-25.50); mother often: 18.48 (8.40-40.66); father occasionally: 10.98 (6.52-18.49); father often: 11.50 (5.96-22.20)] or in children attending other confined places, mainly other houses where people smoked [OR: 2.23 (1.78-2.80)]. CONCLUSIONS: Children's SHS exposure is nowadays an unresolved major public health problem in Spain. After the ban of smoking in public places health care professionals should put more emphasis to the parents on the importance of controlling the exposure of their children in private spaces.

Maternal thyroid dysfunction during gestation, preterm delivery, and birthweight. The Infancia y Medio Ambiente Cohort, Spain.

BACKGROUND: Maternal clinical thyroid disorders can cause reproductive complications. However, the effects of mild thyroid dysfunctions are not yet well established. The aim was to evaluate the association of maternal thyroid function during the first half of pregnancy with birthweight and preterm delivery. METHODS: We analysed data on 2170 pregnant women and their children from a prospective population-based cohort study in four Spanish areas. Mid-gestation maternal serum and urine samples were gathered to determine thyroid-stimulating hormone (TSH), free thyroxine (fT4 ), and urinary iodine concentration (UIC). Thyroid status was defined according to percentile distribution as: euthyroid (TSH and fT4 >5th and <95th percentiles); hypothyroxinaemia (fT4 < 5 th percentile and TSH normal), hypothyroidism (TSH > 95th percentile and fT4 normal or <5th percentile), hyperthyroxinaemia (fT4 > 95 th percentile and TSH normal), and hyperthyroidism (TSH < 5 th percentile and fT4 normal or >95th percentile). Response variables were birthweight, small and large for gestational age (SGA/LGA), and preterm delivery. RESULTS: An inverse association of fT4 and TSH with birthweight was found, the former remaining when restricted to euthyroid women. High fT4 levels were also associated with an increased risk of SGA [odds ratio, 95% confidence interval (CI) 1.28 (95% CI 1.08, 1.51)]. Mean birthweight was higher in the hypothyroxinaemic group (ß = 109, P < 0.01). Iodine intake and UIC were not associated with birth outcomes. CONCLUSIONS: High maternal fT4 levels during the first half of pregnancy were related to lower birthweight and increased risk of SGA newborns, suggesting that maternal thyroid function may affect fetal growth, even within the normal range.

Synergism between exposure to mercury and use of iodine supplements on thyroid hormones in pregnant women.

OBJECTIVE: To evaluate the association between mercury exposure and thyroid-stimulating hormone (TSH), total triiodothyronine (TT3) and free thyroxine (FT4) levels during pregnancy as well as to explore if there is any synergic action between mercury and intake of iodine from different sources. METHODS: The study population was 1407 pregnant women participating in the Spanish INMA birth cohort study. Total mercury concentrations were analyzed in cord blood. Thyroid hormones (THs) were measured in serum samples collected at 13.2±1.5 weeks of gestation. The association between mercury and TH levels was evaluated with multivariate linear regression models. Effect modification caused by iodine intake from supplements and diet was also evaluated. RESULTS: The geometric means of TSH, TT3, FT4 and mercury were 1.1µU/L, 2.4nmol/L, 10.5pmol/L and 7.7µg/L, respectively. Mercury levels were marginally significantly associated with TT3 (ß: -0.05; 95%CI: -0.10, 0.01), but were neither associated with TSH nor FT4. The inverse association between mercury and TT3 levels was stronger among the iodine supplement consumers (-0.08; 95%CI: -0.15, -0.02, interaction p-value=0.07). The association with FT4 followed the same pattern, albeit not significant. CONCLUSION: Prenatal mercury exposure was inversely associated with TT3 levels among women who took iodine supplements during pregnancy. These results could be of public health concern, although further research is needed.