Exposure misclassification due to residential mobility during pregnancy

Objectives: Pregnant women are a highly mobile group, yet studies suggest exposure error due to migration in pregnancy is minimal. We aimed to investigate the impact of maternal residential mobility on exposure to environmental variables (urban fabric, roads and air pollution (PM10 and NO2)) and socio-economic factors (deprivation) that varied spatially and temporally. Methods: We used data on residential histories for deliveries at >= 24 weeks gestation recorded by the Northern Congenital Abnormality Survey, 2000-2008 (n = 5399) to compare: (a) exposure at conception assigned to maternal postcode at delivery versus maternal postcode at conception, and (b) exposure at conception assigned to maternal postcode at delivery versus mean exposure based on residences throughout pregnancy. Results: In this population, 24.4% of women moved during pregnancy. Depending on the exposure variable assessed, 1-12% of women overall were assigned an exposure at delivery >1SD different to that at conception, and 2-25% assigned an exposure at delivery >1SD different to the mean exposure throughout pregnancy. Conclusions: To meaningfully explore the subtle associations between environmental exposures and health, consideration must be given to error introduced by residential mobility. (C) 2015 The Authors. Published by Elsevier GmbH.