Urban-rural residence and birth defects prevalence in Texas: a phenome-wide association study

Some assessments indicate the prevalence of certain birth defects varies by urban-rural status. We evaluated associations between urban-rural residence and a spectrum of birth defects, using a phenome-wide association study approach in Texas, a state with large urban centers and expansive rural areas.

Data for birth defects and livebirths during 1999-2015 were obtained from the Texas Birth Defects Registry and the Center for Health Statistics. Maternal residence was classified as urban or rural, and prevalence ratios (PR) and 95% confidence intervals (CI) were calculated for any defect and 140 specific defects by Poisson regression.

Overall, birth defects were less frequent in rural compared to urban counties (PR = 0.88, 95% CI: 0.87-0.89). Twelve specific defects were less prevalent in rural counties, including ventricular septal defects (VSDs; PR = 0.76, 95% CI: 0.73-0.79) and hypospadias (PR = 0.86, 95% CI: 0.82-0.89). For some birth defects, including VSDs, there was evidence of decreasing prevalence with decreasing population size.

In our large population-based assessment, we demonstrated that several birth defects were less prevalent in rural counties, suggesting that characteristics of urban settings may be relevant to their etiologies, diagnosis, or surveillance. Further research is needed to identify specific exposures underlying these associations.

There are few studies of birth defects prevalence in urban versus rural settings. To address this, we investigated a comprehensive range of birth defects, including several rare defects that have not been previously studied, in a large and diverse population. We identified 12 structural birth defects that were less prevalent in rural areas. Findings suggest possible differential exposures among urban and rural women, and/or possible underdiagnosis of certain birth defects in rural areas. Findings highlight the need for further study of geographically referenced risk factors for birth defects, and of the completeness of birth defects ascertainment in rural areas.