While some causes of birth defects are known (i.e., chromosomal damage), researchers believe that unidentified environmental factors may also contribute to their development. In North Carolina, birth defect rates exhibit a significant amount of spatial variation. Traditional environmental health studies assume that these patterns are due to factors in a mother's environment, such as proximity to a hazardous waste site, that cause birth defects to occur. However, there is also evidence that birth defects are related to behavioral and economic risk factors, such as smoking and poor prenatal care. Spatial patterns of birth defects may therefore be due to the fact that individuals with similar backgrounds and risk factors live in the same geographic area, producing larger area-level patterns of disease. Traditional environmental health studies ignore geographic clustering of people with similar risk factors and use very simple methods to determine exposure to an environmental contaminant. Thus, they may incorrectly attribute spatial patterns of birth defects to environmental hazards rather than socioeconomic factors. This study will develop new theories and methods for examining which of these factors are most important in explaining the geographic variation of two birth defects in North Carolina: orofacial clefts and gastroschisis. Specific study questions include: 1) Is the clustering of birth defects a consequence of compositional factors (i.e. people with similar socioeconomic backgrounds living near each other)? 2) If compositional factors are controlled for, what additional environmental factors explain spatial variability in birth defects (i.e. proximity to hazardous waste)? 3) Do models using hydrogeography to define areas of high contamination risk estimate the risk of birth defects better than models using Euclidean distance? Seven years of data from the NC Birth Defects Monitoring Program and Office of Vital Statistics will be used to examine these questions. Individual-level birth data will be integrated with area-level socioeconomic data and the location of environmental hazards using a Geographic Information System (GIS). Analytical methods include a statistical cluster analysis and a case-control study with spatial multi-level regression models to determine which socioeconomic and environmental factors explain variation in birth defect outcomes.
The presence or absence of environmental contaminants and socioeconomic characteristics and the geographic extent of such factors can offer important insights into the causes of birth defects. However, the complex interactions between people and their environment make it difficult to determine the relative importance of different social, economic and environmental factors. This study offers an interdisciplinary opportunity to merge geographic and epidemiological theories and methods for birth defects research. It applies geographical theories and methods (i.e. disease ecology, hydrological modeling and spatial statistics) to traditional epidemiological research in order to further our understanding of how human-environment interactions affect chronic conditions such as birth defects. The methodologies employed are innovative; they have not been used in this subject area before and will provide a model for conducting future environmental research. Ultimately, this study will provide new findings about the environmental and socioeconomic determinants of orofacial clefts and gastroschisis. Such findings have important policy implications and can be integrated into health promotion programs seeking to prevent birth defects.
