The collection of child urine at 9 and 4.5 y of age and maternal urine in early pregnancy (on average at GW8) has been described in detail elsewhere (Ahmed et al. 2014 (link); Raqib et al. 2017 (link); Vahter et al. 2006 (link)). In short, spot urine samples were collected in trace element–free 24-mL polyethylene bottles either at health care facilities in Matlab or at home. Samples were stored in refrigerators until the end of the day when they were transferred to the hospital laboratory for further storage at −70°C . Blood collection was performed at the health care facilities. Children’s blood samples at 9 y of age were collected in sodium heparin tubes (Vacuette; Greiner Bio-One International AG), whereas the children’s blood samples at 4.5 y of age and the mothers’ blood samples at GW14 were collected in lithium heparin tubes (Monovette, Sarstedt AG & Co.). The blood samples were kept cold and they were transported to the hospital laboratory within a couple of hours for immediate separation of plasma and erythrocytes; the different aliquots were thereafter stored at −70°C .