Study Population

This study was conducted within the Human Early Life Exposome (HELIX) project (Maitre et al. 2018; Vrijheid et al. 2014), which draws resources from six existing European longitudinal population-based birth cohorts: Born in Bradford (United Kingdom; BiB) (Wright et al. 2013); Étude des Déterminants pré et postnatals du développement et de la santé de l’ENfant (France; EDEN) (Drouillet et al. 2009); INfancia y Medio Ambiente (Spain; INMA) (Guxens et al. 2012); Kaunas Cohort (Lithuania; KANC) (Grazuleviciene et al. 2009); Norwegian Mother and Child Cohort Study (Norway; MoBa) (Magnus et al. 2016), and Rhea (Greece) (Chatzi et al. 2017). Our study consisted of 818 mothers and 1,288 children and included information on maternal diet, child’s diet, and measured levels of environmental contaminants during pregnancy and childhood. This subsample, called the HELIX subcohort, is nested within the entire HELIX cohort (n=32,000 mother–child pairs) by inclusion of approximately 200 pairs from each cohort (Maitre et al. 2018). The detailed description of the study design and population is provided by Maitre et al. (2018). In brief, the included children were between 6 and 11 y of age, and the data and biological sample collection was conducted from 2013 to 2015. Eligibility criteria for inclusion in the subcohort were a) age 6–11 y at the time of the visit, with a preference for ages 7–9 y if possible; b) sufficient stored pregnancy blood and urine samples available for analysis of prenatal exposure biomarkers; c) complete address history available from first to last follow-up point; and d) no serious health problems that may affect the performance of the clinical testing or impact the volunteer’s safety (e.g., acute respiratory infection). Each cohort selected participants at random from the eligible pool within the entire cohort and invited them to participate in this subcohort until the required number of participants was reached.