US County-Level Variation in Preterm Birth Rates, 2007-2019

Area of Science:

• Public Health
• Epidemiology
• Maternal and Child Health

Background:

• Preterm birth is a major cause of infant mortality and morbidity.
• National preterm birth rates may obscure critical geographic variations and trends at the county level.

Purpose of the Study:

• To estimate age-standardized preterm birth rates across US counties from 2007 to 2019.
• To analyze geographic disparities and trends in preterm birth rates at the county level.

Main Methods:

• Utilized a serial cross-sectional study design with US National Center for Health Statistics data (2007-2019).
• Calculated age-standardized preterm birth rates using a validated small area estimation model (hierarchical Bayesian spatiotemporal model).
• Employed log-linear regression to assess changes in preterm birth rates and their association with the Social Vulnerability Index.

Main Results:

• Significant geographic variation in preterm birth rates was observed, with a notable difference between highest and lowest percentile counties.
• Counties in the Southeast consistently exhibited higher rates compared to California and New England.
• While national rates remained stable, nearly 1 in 6 counties experienced increases; higher Social Vulnerability Index quartiles correlated with elevated preterm birth rates.

Conclusions:

• Substantial geographic disparities in preterm and early preterm birth rates exist, linked to place-based social disadvantage.
• National-level stability in preterm birth rates conceals concerning increases in numerous individual counties.
• Findings underscore the importance of addressing localized social determinants to mitigate preterm birth disparities.