Urban versus rural residence and occurrence of septal heart defects in Texas

There is conflicting information on the association between urban/rural residence of mothers and atrial septal defect (ASD) or ventricular septal defect (VSD) in their offspring. Few studies have compared multiple measures of urban/rural residence.

Data were taken from the Texas Birth Defects Registry, 1999-2003. Poisson regression was used to compare crude and adjusted birth prevalence.

Three broad urban/rural measures, namely, the rural urban continuum code (RUCC), urban influence code (UIC), and rural urban commuting area (RUCA), were correlated with each other, but much less correlated with percentage of land in crops. ASD showed few consistent patterns with RUCC, UIC, and RUCA but was more prevalent in counties with higher cropland percentage. For example, counties with > or =50% cropland had a prevalence ratio (PR) for isolated ASD of 3.49 (95% confidence interval [CI]: 2.85-4.24) compared to counties with <15% cropland. VSD was less prevalent in rural areas using RUCC, UIC, and RUCA. For example, for isolated VSD, small towns/rural areas had a PR of 0.64 (95% CI: 0.51-0.78) compared to urban core areas using RUCA. The pattern was seen among mild cases of VSD but not among severe cases. VSD was not associated with percentage cropland.

The measure of urban/rural status can greatly affect associations with certain birth defects. More prevalent ASD in areas with greater percentage cropland suggests that agricultural chemicals may be relevant. Mild cases of VSD but not severe cases were less prevalent in rural areas, suggesting that variation in detection may be largely responsible.