Substantial variations found in US county-level preterm birth rates

Key takeaways:

• The gap between the highest and lowest counties for preterm births was 20.7 per 100 live births in 2007.
• Preterm birth rates increased in 15.4% of U.S. counties from 2007 to 2019.

Researchers found substantial variations in U.S. county-level preterm and early preterm birth rates, which were associated with local social disadvantages, according to an analysis published in JAMA Network Open.

“A large body of research has documented significant county-level variation in a variety of other health outcomes,” Sadiya S. Khan, MD, MSc, Magerstadt Professor of Cardiovascular Epidemiology and associate professor of medicine (cardiology) and preventive medicine (epidemiology) at Northwestern University Feinberg School of Medicine, and colleagues wrote. “However, less is known about county-level rates, trends and correlates of geographic variation in preterm birth.”

Khan and colleagues conducted a serial cross-sectional study using data from 51,044,482 live births in 2,383 U.S. counties from 2007 to 2019 from the National Center for Health Statistics. Researchers evaluated age-standardized preterm birth and early preterm birth rates by county and year as well as percent change in preterm birth rates.

The national age-standardized preterm birth rate was 12.6 per 100 live births in 2007. Preterm birth rates had significant county-level variation, with an absolute difference between the 90th and 10th percentile counties of 6.4 per 100 live births. In 2007, the gap between the highest and lowest counties for preterm birth was 20.7 per 100 live births, and that gap was similar in 2019. Several Southeast counties consistently had the highest preterm birth rates compared with California and New England counties, which had the lowest preterm birth rates.

The percent change in preterm birth rates from 2007 to 2019 at the national level was a decrease of 5%, which was not statistically significant. In addition, from 2007 to 2019, preterm birth rates increased in 15.4% of U.S. counties.

Across all maternal age groups, the absolute and relative geographic inequalities were similar. Being in the higher quartile of the Social Vulnerability Index was associated with higher preterm birth rates compared with the lower quartiles (RR = 1.34; 95% CI, 1.31-1.36).

Researchers observed similar findings for early preterm birth rates.

“Policymakers, researchers and clinicians may use these county-level prevalence and trend estimates to inform the development and evaluation of interventions to reduce place-based disparities in preterm birth and thus improve health for both the birthing individual and offspring,” the researchers wrote.