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Pregnant women who resided in census tracts that had high measures of social vulnerability were at increased risk for preterm birth, according to a retrospective cohort study.

Using the CDC's , researchers found that women who delivered preterm were more likely to live in areas that had high social vulnerabilities, including those related to socioeconomic status, housing composition, and demographics, according to Matthew Givens, MD, of UNC Health Care in Durham, North Carolina, and colleagues.

The association between social vulnerability and risk of preterm birth was strongest in areas that had high vulnerabilities related to socioeconomic status (poverty, unemployment, and education level) and household composition (single-parent households or those caring for dependents), Givens reported at the Society for Maternal-Fetal Medicine annual meeting.

"Though there are many risk factors associated with preterm birth, the identification of people at high risk of preterm birth remains difficult," Givens said in his presentation. He emphasized that breaking the risk down to geographic locations showed that "community factors may affect preterm birth risk beyond individual factors."

Loralei Thornburg, MD, a maternal-fetal medicine specialist at the University of Rochester Medical Center in New York, said that using the Social Vulnerability Index allows public health experts to identify geographic, community-level risks, rather than placing the emphasis on specific patient populations. This improves the ability to enact interventions and promote resilience on a structural level.

"All sorts of domains influence preterm birth, and living in areas with these higher social vulnerability indexes seems to be a risk factor," Thornburg, who was not involved in this study, said in an interview. She added that areas with high social vulnerabilities are places where the medical community needs to place its "bag of gold coins," so to speak, when it comes to addressing the roots of preterm birth risk.

The Social Vulnerability Index is meant to help communities identify areas of strengths and weaknesses for disaster preparedness. It includes 15 social factors to identify social vulnerabilities in census tracts, with overarching themes including socioeconomic status, household composition and disability, minority status and language, and housing type and transportation.

Givens and colleagues conducted a retrospective analysis to determine whether high-vulnerability census tracts were associated with increased odds of preterm birth. They obtained electronic medical records for all singleton and twin pregnancies that occurred from 2014 to 2020 at a single hospital system in North Carolina. Givens's group also obtained home addresses of all study participants during their pregnancy, with the census tract of their residence used for analysis.

Two patient groups were studied: the first consisted of patients considered high risk for spontaneous or medically indicated preterm birth, or who delivered preterm in their current pregnancy. The second group consisted of randomly selected low-risk patients who had no medical comorbidities associated with preterm delivery, or who delivered at term.

The primary outcome was preterm birth at less than 37 weeks; secondary outcomes were preterm birth at less than 34 and 28 weeks. Models were adjusted for Black race, history of preterm birth, smoking during pregnancy, chronic hypertension, diabetes, short cervical length, male fetal sex, and twin pregnancies.

More than 50,000 patients from over 900 census tracts were included. Nearly 9% of mothers delivered at less than 37 weeks, 3% delivered at less than 34 weeks, and 1% delivered at less than 28 weeks.

Mothers who gave birth preterm were more likely to identify as non-Hispanic Black, have at least one prior spontaneous preterm birth, or smoke during pregnancy. This cohort was also more likely to have comorbidities including diabetes and chronic hypertension.

There was an inverse relationship between social vulnerability and gestational age at birth, with more extreme preterm birth occurring as social vulnerability increased.

Givens recognized several limitations to the study, including that it does not establish causality. This study was also unable to account for patients who moved home addresses during the study period and may have spent a significant amount of time in a different census tract. In addition, the Social Vulnerability Index does not capture all health factors that may affect perinatal outcomes.

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