Box 1.

Avon longitudinal study of parents and children

• This is a World Health Organization initiative and is an ongoing, geographically based, population birth cohort study. Sister studies in other European countries (collectively known as ELSPAC) are also in progress⁹
• The cohort study was open to all pregnant women with an estimated date of delivery between 1 April 1991 and 31 December 1992, who were resident in the area formerly known as Avon, in southwest England
• Approximately 14 000 women were recruited (85% of those eligible) while they were still pregnant
• Demographic data for the sample are very similar to data from the 1991 UK census for Avon, but the sample contains fewer very deprived families, families of Asian extraction, and families in which the mother was a teenager when her child was born
• Data collection is prospective and by diverse means, including self completion questionnaires to the mothers, their partners, and (after age 5) the children; physical samples such as mother's antenatal blood, cord blood, teeth, nails, placentas, and blood on subsets of the children; environmental samples; linkage to the hospital and educational records; and a recently established DNA library and cell lines (for the children, the mothers, and their partners)
• The results of a variety of physical and psychometric examinations are available for a random sample of children who were examined between 4 months and 5 years of age and for the whole cohort who have been invited to yearly examinations since the age of 7 (examinations at age 9 are currently taking place)
• Substudies (including the one reported here) covering a range of outcomes in the children have been nested within the main study, and further projects are ongoing