Geospatial associations of traffic density and neighborhood stress with birth outcomes in Milwaukee, 2005-2010

Traffic density has recently been associated with a modest increased risk of preterm birth and low birth weight independent of many other known risk factors. This multilevel study used innovative methods to measure traffic burden and neighborhood stress and their effect on these birth outcomes. We examined these and other factors in a metropolitan area that is highly segregated by race and ethnicity. We estimated traffic density patterns by calculating normalized cumulative average daily traffic (CADT) in relation to the mother’s census block of residence at the time of birth. An index of food inaccessibility was used as an indicator of neighborhood-level stress. The index, created at the census tract-level, is comprised of distance to supermarket, access to a vehicle, and poverty. We examined the spatial associations between traffic density, neighborhood stress, and birth outcomes using ArcGIS (Version 10.1) software and SAS Version 9.4 for all other statistics. Electronic birth records were obtained for all singleton births in Milwaukee County that occurred between January 1, 2005 and December 31, 2010. There were 85,038 singleton births with gestational age and maternal street address available. Addresses were coded by the Wisconsin Vital Statistics Office to the census block level to maintain confidentiality. We depicted CADT and neighborhood stress across the county in relation to birth outcomes. The overall prevalence of preterm birth and low birth weight were 11.72% and 7.48%, respectively, but varied substantially by race-ethnicity and geography. Policy implications of the findings will be discussed.