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Prenatal exposure to organophosphate (OP) pesticides associate with impaired neurodevelopment in humans and animal models. However, much uncertainty exists about the brain structural alterations underlying these associations. The objective of this study was to determine whether maternal OP pesticide metabolite concentrations in urine repeatedly measured during gestation are associated with brain morphology and white matter microstructure in 518 preadolescents aged 9–12 years. Data came from 518 mother–child pairs participating in the Generation R Study, a population-based birth cohort from Rotterdam, the Netherlands. Maternal urine concentrations were determined for 6 dialkylphosphates (DAPs) including 3 dimethyl (DM) and 3 diethyl (DE) alkyl phosphate metabolites, collected at early, mid, and late pregnancy. At child's age 9–12 years, magnetic resonance imaging was performed to obtain T1-weighted images for brain volumes and surface-based cortical thickness and cortical surface area, and diffusion tensor imaging was used to measure white matter microstructure through fractional anisotropy (FA) and mean diffusivity (MD). Linear regression models were fit for the averaged prenatal exposure across pregnancy. DM and DE metabolite concentrations were not associated with brain volumes, cortical thickness, and cortical surface area. However, a 10-fold increase in averaged DM metabolite concentrations across pregnancy was associated with lower FA (B = −1.00, 95%CI = −1.80, −0.20) and higher MD (B = 0.13, 95%CI = 0.04, 0.21). Similar associations were observed for DE concentrations. This study provides the first evidence that OP pesticides may alter normal white matter microstructure in children, which could have consequences for normal neurodevelopment. No associations were observed with structural brain morphology, including brain volumes, cortical thickness, and cortical surface area. • Little is known about the effect of prenatal OP pesticide exposure on offspring brain morphology and white matter. • Maternal urinary concentrations of 6 DAP metabolites were measured during early, mid, and late pregnancy. • MRI was performed to obtain brain volumes, cortical thickness, and cortical surface area in 518 preadolescents. • DTI was used to measure white matter microstructure through fractional anisotropy (FA) and mean diffusivity (MD). • Prenatal exposure to OP pesticides was predictive of lower FA and higher MD, indicating atypical white matter microstructure. [ABSTRACT FROM AUTHOR]

Animal studies suggest that organophosphate (OP) pesticides exposure affects thyroid function, but evidence in humans remains sparse and inconclusive. Gestational exposure is of particular interest, since thyroid hormone is essential for fetal brain development. OP pesticides are able to cross the placental and blood-brain barrier and may interfere with fetal development processes regulated by thyroid hormone. To investigate the association of gestational OP pesticides exposure during pregnancy with maternal and cord blood thyroid hormone concentrations. This study was embedded within Generation R (Rotterdam, the Netherlands), a prospective population-based birth cohort. Mother-child pairs with OP pesticides assessment and maternal (N = 715) or cord blood (N = 482) thyroid hormone measurements were included. OP pesticides exposure was assessed at <18, 18–25, and >25 weeks gestation by measuring six urinary dialkylphosphate (DAP) metabolites. Thyroid stimulating hormone (TSH) and free thyroxine (FT4) were measured in maternal and cord blood. Maternal measures also included total thyroxine (TT4) and TPO antibodies (TPOAbs). To study the association of creatinine-adjusted DAP metabolite concentrations with thyroid function and TPO antibodies, multivariable linear regression models including relevant confounders were used. There was no association of DAP metabolites with maternal TSH, FT4, TT4 or TPOAb concentrations during pregnancy. Similarly, there was no association of DAP metabolites with cord blood TSH or FT4. Results did not change when DAP concentrations were analyzed at individual time points or as mean gestational exposure. Gestational OP pesticides exposure, as assessed by repeatedly measured urinary DAP metabolite concentrations in an urban population, was not associated with maternal or cord blood thyroid hormone concentrations. These findings do not support a mediating role for serum thyroid hormone availability in the relation of early life exposure to low levels of OP pesticides with child neurodevelopment. However, disruption of the thyroid system at tissue level cannot be excluded. In addition, this is one of the first studies on this subject and measurement error in DAP metabolites might have resulted in imprecise estimates. Future studies should use more urine samples to increase precision and should investigate specific OP pesticide metabolites. • We explored whether gestational OP pesticide exposure is associated with maternal or cord thyroid parameters. • Maternal urinary concentrations of six DAP metabolites were measured during early, mid, and late pregnancy. • DAP metabolite concentrations were 2–3 times higher than those in most other birth cohorts. • Thyroid hormones were measured during early pregnancy and in cord blood. • Maternal DAP concentrations were not associated with maternal or cord blood thyroid hormone concentrations. [ABSTRACT FROM AUTHOR]

Prenatal exposure to organophosphate (OP) pesticides has been associated with altered neuronal cell development and behavioral changes in animal offspring. However, the few studies investigating the association between prenatal OP pesticide exposure and neurodevelopmental outcomes such as Attention-Deficit Hyperactivity Disorder (ADHD) and autistic traits in children produced mixed findings. The objective of the present study was to examine whether maternal urinary concentrations of OP pesticide metabolites are associated with ADHD and autistic traits in children participating in the Generation R Study, a population-based birth cohort from Rotterdam, the Netherlands. Maternal concentrations of 6 dialkylphosphates (DAPs) were measured using gas chromatography coupled with tandem mass spectrometry in urine samples collected at <18 weeks, 18‐25 weeks, and > 25 weeks of gestation in 784 mother-child pairs. DAP metabolite concentrations were expressed as molar concentrations divided by creatinine levels and log 10 transformed. ADHD traits were measured at ages 3, 6, and 10 years using the Child Behavior Checklist (CBCL) (n = 781) and autistic traits were measured at age 6 years using the Social Responsiveness Scale (SRS) (n = 622). First, regression models were fit for the averaged prenatal exposure across pregnancy. Second, we investigated associations for each collection phase separately, and applied a mutually adjusted model in which the effect of prenatal DAP concentrations from each time period on ADHD and autistic traits were jointly estimated. All associations were adjusted for relevant confounders. Median DAP metabolite concentration was 309 nmol/g creatinine at <18 weeks, 316 nmol/g creatinine at 18–25 weeks, and 308 nmol/g creatinine at >25 weeks of gestation. Overall, DAP metabolite concentrations were not associated with ADHD traits. For instance, a log10 increase in averaged total DAP concentrations across gestation was not associated with a lower ADHD score (-0.03 per SD 95 CI: −0.28 to 0.23). Similarly, no associations between maternal DAP concentrations and autistic traits were detected. In this study of maternal urinary DAP metabolite concentrations during pregnancy, we did not observe associations with ADHD and autistic traits in children. These are important null observations because of the relatively high background DAP concentrations across pregnancy, the relatively large sample size, and the 10-year follow-up of the offspring. Given the measurement error inherent in our OP pesticide exposure biomarkers, future studies using more urine samples are needed to accurately measure OP pesticide exposure over pregnancy in relation to ADHD and autistic traits. • We explored whether prenatal exposure to OP pesticides is associated with ADHD and autistic traits in children • Maternal urinary concentrations of six DAP metabolites were measured during early, mid, and late pregnancy • DAP metabolite concentrations in this study were 2-3 times higher compared with concentrations measured in most other studies • Maternal DAP concentrations were not associated with ADHD and autistic traits in children. [ABSTRACT FROM AUTHOR]