Purpose: The etiology of orofacial clefts is complex and relatively unknown. Variation in cleft lip with or without palate (CLP) and cleft palate alone (CP) was examined in Texas across urban-rural residence (1999 to 2003).
Methods: Cases came from the Texas Birth Defects Registry (1,949 CLP and 1,054 CP) and denominator data came from vital records (254 counties; 1,827,317 live births). Variation in maternal residence was measured using four classification schemes: Rural Urban Continuum Codes, Urban Influence Codes, percentage of county in cropland, and Rural Urban Commuting Areas. Poisson regression was used to calculate rate ratios, adjusted for infant sex, plurality, gestational age, maternal parity, age, race/ethnicity, and education.
Results: Compared to the most urban referent category, living in more rural areas was associated with an increased adjusted risk of CLP. For example, the Rural-Urban Continuum Codes demonstrated elevated risks for CLP in "thinly populated areas" compared to "metropolitan-urban areas" (adjusted prevalence ratio = 1.9; 95% confidence intervals (CI) 1.2-2.8); CP was not similarly associated. Percentage of county cropland was not consistently associated with any outcome.
Conclusion: The association patterns between non-urban residence and risk of CLP, except for percentage of cropland, suggests a constellation of exposures that may differ across urban-rural residence.