Birth weight reflects intrauterine growth and wellbeing and is recognised globally as an indicator of perinatal and infant health. A number of studies have suggested that occupation, air pollution and chlorination by-products in drinking water may be associated with low birth weight/intra uterine growth retardation (Nieuwenhuijsen et al 2000, Sram et al 2005, Farrow et al 1998, Chia et al 2004, Rylander and Kallen 2005), but the evidence is inconclusive, partly as a result of limited exposure assessments in the epidemiological studies that have been conducted. A large prospective birth cohort study is required to provide conclusive evidence about the link between occupation, chlorination by-products and air pollution on birth weight. The overall aim of this study is to bring together a multi-disciplinary team of physicians, epidemiologists, geneticists, environmental scientists, social scientists and statistical modellers to build capacity and lay the ground work for further studies to investigate the relationship, if any, between occupational factors, traffic related air pollution and chlorination disinfection by-products (DBPs) in drinking water and intra uterine growth retardation/low birth weight, taking into account known potential confounders such as smoking and ethnicity in the Born in Bradford study of 10,000 pregancies. The main focus of the work is the collection of information for the validation of exposure estimates, together with the initiation of data collection for the exposure modelling and preparing a strategy for linking them to health data.