The Avon Longitudinal Study of Parents and Children (ALSPAC) is an ongoing population based birth cohort study examining influences on health and development across the life course. The core enrolled sample consists of 14 541 pregnant women resident in the former county of Avon in south west England (United Kingdom) with expected delivery dates between 1 April 1991 and 31 December 1992.21 Of the 14 062 live births, 13 798 were singletons or first born of twins, and were alive at 1 year of age. Participants have been followed up regularly since recruitment through questionnaires and attendance at research clinics. Information about ALSPAC is available on the study website (www.bristol.ac.uk/alspac), which includes details of all available data through a fully searchable data dictionary (www.bris.ac.uk/alspac/researchers/data-access/data-dictionary). Written informed consent was obtained from participants after the procedures had been fully explained.
