County-level preterm birth risk high for women with more social determinants of health

Key takeaways:

• Very high level of social determinants of health was linked to increased risk for preterm birth.
• Higher physical health, mental health and substance abuse, and general health care were all tied to preterm birth.

County-level preterm birth risk was higher among women with more physical, social and health risk factors as measured by a novel county-level index to quantify maternal vulnerability to adverse outcomes.

The Maternal Vulnerability Index (MVI) is a county-level index measuring maternal community risk factors for adverse maternal health outcomes. MVI provides a county-level index of 43 indicators that are categorized into six themes reflecting physical, social and health care landscapes, researchers noted.

“Preliminary data show an association between higher MVI and maternal mortality. The extent to which the MVI affects infant health is unknown,” Elizabeth G. Salazar, MD, a research fellow and attending neonatologist in the division of neonatology at The Children’s Hospital of Philadelphia, Philadelphia, and colleagues wrote. “Since preterm birth is a pregnancy outcome with significant implications for infant health, the objective of this study was to examine the association of the MVI with preterm birth and severity of preterm birth, both overall and stratified by MVI theme.”

In this retrospective cohort study, Salazar and colleagues identified 3,659,099 singleton births at 22 to 44 weeks gestation using U.S. National Vital Statistics System data from 2018. Researchers utilized the MVI to assess its association with preterm birth in this cohort.

The primary outcome was preterm birth, defined as birth at gestational age less than 37 weeks. Secondary outcomes included extreme (gestational age 28 weeks or less), very (gestational age 29 to 31 weeks), moderate (gestational age 32 to 33 weeks) and late (gestational age 34 to 36 weeks) preterm birth.

Overall, 8.2% of births were preterm (48.9% girls), with 0.5% categorized as extreme preterm, 0.7% as very preterm, 0.9% as moderate preterm and 6.1% as late preterm. Most mothers were non-Hispanic white (52.1%), followed by Hispanic (23.6%), non-Hispanic Black (14.5%), Asian or Pacific Islander (6.8%), more than one race/ethnicity (2.2%) and American Indian/Alaska Native (0.8%).

Results published in JAMA Network Open, demonstrated that those with very high MVI had higher preterm birth rates (10.2% vs. 7%; P < .001). Very high MVI was associated with increased preterm birth in both unadjusted (OR = 1.5; 95% CI, 1.45-1.56) and adjusted (OR = 1.07; 95% CI, 1.01-1.13) analyses compared with women with very low MVI.

MVI had the largest association with extreme preterm birth (aOR = 1.18; 95% CI, 1.07-1.29). Researchers observed that higher MVI in the themes of physical health (aOR = 1.09; 95% CI, 1.03-1.14), mental health and substance abuse (aOR = 1.09; 95% CI, 1.03-1.16) and general health care (aOR = 1.08; 95% CI, 1.02-1.15) were all associated with overall preterm birth.

Very high mental health and substance abuse MVI was linked to late (aOR = 1.1; 95% CI, 1.03-1.17) and moderate (aOR = 1.12; 95% CI, 1.03-1.23) preterm birth. In addition, very high general health care MVI was linked to late preterm birth (aOR = 1.1; 95% CI, 1.03-1.18). However, very high physical health and socioeconomic MVI were both associated with extreme preterm birth (aOR = 1.13; 95% CI, 1.05-1.22).

“Our findings support the MVI as a useful index to examine the role of maternal community-level risk factors in preterm birth,” the researchers wrote. “Variability in this measure highlights the importance of unique state and county-specific policies to address community-specific maternal risks of preterm birth.”