The current study was part of a large prospective population-based birth cohort, the Amsterdam Born Children and their Development (ABCD) study. The main goal of this study is to assess the extent to which maternal conditions during pregnancy and early-life conditions explain the child's health at birth as well as in later life (http://www.abcd-study.nl). This study was conducted according to the guidelines laid down in the Declaration of Helsinki and all procedures involving human subjects were approved by the Central Committee on Research Involving Human Subjects, the Medical Research Ethics Committees of the participating hospitals, and the Registration Committee of the municipality of Amsterdam. Written informed consent was obtained from all subjects.