title: Exposure misclassification due to residential mobility during pregnancy.
abstract: OBJECTIVE
  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 >1 SD different to that at conception, and 2-25% assigned an exposure at delivery >1 SD 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.
authors.affiliation: MRC-PHE Centre for Environment & Health, Department of Epidemiology & Biostatistics, Imperial College London, United Kingdom; Institute of Health & Society, Newcastle University, Newcastle upon Tyne, United Kingdom. Electronic address: susan.hodgson@imperial.ac.uk.
authors.forename: Susan
authors.initials: S
authors.lastname: Hodgson
authors.affiliation: School of Biology, Newcastle University, Newcastle upon Tyne, United Kingdom; Royal (Dick) School of Veterinary Studies, University of Edinburgh, Edinburgh, United Kingdom. Electronic address: lurzpww@gmail.com.
authors.forename: Peter W W
authors.initials: PW
authors.lastname: Lurz
authors.affiliation: School of Biology, Newcastle University, Newcastle upon Tyne, United Kingdom. Electronic address: mark.shirley@ncl.ac.uk.
authors.forename: Mark D F
authors.initials: MD
authors.lastname: Shirley
authors.affiliation: Regional Maternity Survey Office, Newcastle upon Tyne, United Kingdom. Electronic address: marybythell@gmail.com.
authors.forename: Mary
authors.initials: M
authors.lastname: Bythell
authors.affiliation: Institute of Health & Society, Newcastle University, Newcastle upon Tyne, United Kingdom; Regional Maternity Survey Office, Newcastle upon Tyne, United Kingdom. Electronic address: judith.rankin@newcastle.ac.uk.
authors.forename: Judith
authors.initials: J
authors.lastname: Rankin
mesh_terms: D000328:Adult; D000397:Air Pollution / Q000706:statistics & numerical data; D000013:Congenital Abnormalities; D004739:England; D005260:Female; D006306:Health Surveys / Q000706:statistics & numerical data; D063426:Human Migration / Q000706:statistics & numerical data*; D006801:Humans; D018811:Maternal Exposure / Q000145:classification* / Q000706:statistics & numerical data; D011247:Pregnancy; D011256:Pregnancy Outcome; D011446:Prospective Studies; D012042:Registries; D012959:Socioeconomic Factors
keywords: Environmental exposure; Exposure assessment; Exposure error; Maternal exposure; Residential mobility