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. 2023 May 1;6(5):e2315306.
doi: 10.1001/jamanetworkopen.2023.15306.

County-Level Maternal Vulnerability and Preterm Birth in the US

Elizabeth G Salazar  1   2 , Diana Montoya-Williams  1   2   3 , Molly Passarella  1 , Carolyn McGann  1   3 , Kathryn Paul  1 , Daria Murosko  1 , Michelle-Marie Peña  1   2   4 , Robin Ortiz  5   6 , Heather H Burris  1   2   3 , Scott A Lorch  1   2   3 , Sara C Handley  1   2   3
Affiliations

County-Level Maternal Vulnerability and Preterm Birth in the US

Elizabeth G Salazar et al. JAMA Netw Open. .

Abstract

Importance: Appreciation for the effects of neighborhood conditions and community factors on perinatal health is increasing. However, community-level indices specific to maternal health and associations with preterm birth (PTB) have not been assessed.

Objective: To examine the association of the Maternal Vulnerability Index (MVI), a novel county-level index designed to quantify maternal vulnerability to adverse health outcomes, with PTB.

Design, setting, and participants: This retrospective cohort study used US Vital Statistics data from January 1 to December 31, 2018. Participants included 3 659 099 singleton births at 22 plus 0/7 to 44 plus 6/7 weeks of gestation born in the US. Analyses were conducted from December 1, 2021, through March 31, 2023.

Exposure: The MVI, a composite measure of 43 area-level indicators, categorized into 6 themes reflecting physical, social, and health care landscapes. Overall MVI and theme were stratified by quintile (very low to very high) by maternal county of residence.

Main outcomes and measures: The primary outcome was PTB (gestational age <37 weeks). Secondary outcomes were PTB categories: extreme (gestational age ≤28 weeks), very (gestational age 29-31 weeks), moderate (gestational age 32-33 weeks), and late (gestational age 34-36 weeks). Multivariable logistic regression quantified associations of MVI, overall and by theme, with PTB, overall and by PTB category.

Results: Among 3 659 099 births, 298 847 (8.2%) were preterm (male, 51.1%; female, 48.9%). Maternal race and ethnicity included 0.8% American Indian or Alaska Native, 6.8% Asian or Pacific Islander, 23.6% Hispanic, 14.5% non-Hispanic Black, 52.1% non-Hispanic White, and 2.2% with more than 1 race. Compared with full-term births, MVI was higher for PTBs across all themes. Very high MVI was associated with increased PTB in unadjusted (odds ratio [OR], 1.50 [95% CI, 1.45-1.56]) and adjusted (OR, 1.07 [95% CI, 1.01-1.13]) analyses. In adjusted analyses of PTB categories, MVI had the largest association with extreme PTB (adjusted OR, 1.18 [95% CI, 1.07-1.29]). Higher MVI in the themes of physical health, mental health and substance abuse, and general health care remained associated with PTB overall in adjusted models. While the physical health and socioeconomic determinant themes were associated with extreme PTB, physical health, mental health and substance abuse, and general health care themes were associated with late PTB.

Conclusions and relevance: The findings of this cohort study suggest that MVI was associated with PTB even after adjustment for individual-level confounders. The MVI is a useful measure for county-level PTB risk that may have policy implications for counties working to lower preterm rates and improve perinatal outcomes.

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Conflict of interest statement

Conflict of Interest Disclosures: Dr Salazar reported receiving grant funding from the National Institutes of Health (NIH) outside the submitted work. Dr Montoya-Williams reported receiving grant funding from the NIH outside the submitted work. Ms Passarella reported receiving grant funding from the NIH during the conduct of the study. Dr Ortiz reported paid consulting with the UCLA-UCSF ACEs Aware Family Resilience Network and receiving funding as a research advisor for the Courage First helpline, outside the submitted work. Dr Handley reported receiving grant funding from American Academy of Pediatrics outside the submitted work. No other disclosures were reported.

Figures

Figure 1.
Figure 1.. Unadjusted and Adjusted Associations of Maternal Vulnerability Index (MVI) With Preterm Birth by Gestational Age Categories Compared With Full-term Births
Associations are reported as odds ratios (ORs). The MVI scores range from 0 (lowest vulnerability) to 100 (highest vulnerability). Where indicated, ORs are adjusted for age, race and ethnicity, insurance, educational attainment, Kotelchuk index of adequate prenatal care, body mass index, nulliparity, preexisting hypertension, smoking during pregnancy, rurality, infant sex, and US Census region.
Figure 2.
Figure 2.. Unadjusted and Adjusted Associations of Maternal Vulnerability Index (MVI) Themes of Reproductive Health Care, Physical Health, Mental Health and Substance Abuse, and General Health Care, With Preterm Births Compared With Full-term Births
Preterm birth indicates gestational age younger than 37 weeks. Associations are reported as odds ratios (ORs). The MVI scores range from 0 (lowest vulnerability) to 100 (highest vulnerability). Where indicated, ORs are adjusted for age, race and ethnicity, insurance, educational attainment, Kotelchuk index of adequate prenatal care, body mass index, nulliparity, preexisting hypertension, smoking during pregnancy, rurality, infant sex, and US Census region.
Figure 3.
Figure 3.. Unadjusted and Adjusted Associations of Maternal Vulnerability Index (MVI) Themes of Socioeconomic Determinants and Physical Environment With Preterm Births Compared With Full-term Births
Preterm birth indicates gestational age younger than 37 weeks. Associations are reported as odds ratios (ORs). The MVI scores range from 0 (lowest vulnerability) to 100 (highest vulnerability). Where indicated, ORs are adjusted for age, race and ethnicity, insurance, educational attainment, Kotelchuk index of adequate prenatal care, body mass index, nulliparity, preexisting hypertension, smoking during pregnancy, rurality, infant sex, and US Census region.
Figure 4.
Figure 4.. Unadjusted and Adjusted Associations of Maternal Vulnerability Index (MVI) With Preterm Births by Gestational Age Categories Compared With Full-term Births
Associations are reported as odds ratios (ORs). The MVI scores range from 0 (lowest vulnerability) to 100 (highest vulnerability). Where indicated, ORs are adjusted for age, race and ethnicity, insurance, educational attainment, Kotelchuk index of adequate prenatal care, body mass index, nulliparity, preexisting hypertension, smoking during pregnancy, rurality, infant sex, and US Census region. Late preterm birth indicates 34 to less than 37 weeks; moderate preterm birth, 32 to less than 34 weeks; very preterm birth, 28 to less than 32 weeks; extreme preterm birth, less than 28 weeks.
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