Wildfire-specific fine particulate matter and preterm birth: a US ECHO Cohort analysis

Allison R Sherris¹, Logan C Dearborn², Dana E Goin³, Christine T Loftus², Adam A Szpiro⁴, Joan A Casey², Sindana D Ilango⁵, Jyoti Angal⁶, Deborah H Bennett⁷, Miatta A Buxton⁸, Carlos A Camargo Jr⁹, Kecia N Carroll¹⁰, Marissa L Childs², Camille Cioffi¹¹, Lisa A Croen¹², Dana Dabelea¹³, Stephanie M Eick¹⁴, Shohreh F Farzan¹⁵, Assiamira Ferrara¹², Erika Garcia¹⁵, Alison Gemmill¹⁶, Frank Gilliland¹⁵, Rima Habre¹⁵, Irva Hertz-Picciotto⁷, Alison E Hipwell¹⁷, Deborah Hirtz¹⁸, Margaret R Karagas¹⁹, Daphne Koinis-Mitchell²⁰, Amii M Kress²¹, Leslie D Leve¹¹, Donghai Liang¹⁴, Kristen Lyall²², Lacey A McCormack²³, Cindy T McEvoy²⁴, Hooman Mirzakhani²⁵, Rachel Morello-Frosch²⁶, Zhongzheng Niu¹⁵, Thomas G O'Connor²⁷, Alicia K Peterson¹², Rebecca J Schmidt²⁸, Catherine J Karr²⁹, Amy M Padula³⁰; ECHO Cohort Consortium

Affiliations

¹ Department of Environmental and Occupational Health Sciences, University of Washington, Seattle, WA, USA. Electronic address: asherris@uw.edu.
² Department of Environmental and Occupational Health Sciences, University of Washington, Seattle, WA, USA.
³ Mailman School of Public Health, Columbia University, New York, NY, USA.
⁴ Department of Biostatistics, University of Washington, Seattle, WA, USA.
⁵ Department of Epidemiology, University of Washington, Seattle, WA, USA.
⁶ Department of Pediatrics, Avera Research Institute, University of South Dakota School of Medicine, Sioux Falls, SD, USA.
⁷ Department of Public Health Sciences, University of California, Davis, Davis, CA, USA.
⁸ Department of Epidemiology, University of Michigan, Ann Arbor, MI, USA.
⁹ Department of Emergency Medicine, Massachusetts General Hospital, Harvard Medical School, Boston, MA, USA.
¹⁰ Pediatrics and Environmental Medicine, Icahn School of Medicine at Mount Sinai, New York City, NY, USA.
¹¹ Prevention Science Institute, University of Oregon, Eugene, OR, USA.
¹² Division of Research, Kaiser Permanente Northern California, Pleasanton, CA, USA.
¹³ Lifecourse Epidemiology of Adiposity & Diabetes Center, Colorado School of Public Health, University of Colorado Anschutz Medical Campus, Aurora, CO, USA.
¹⁴ Gangarosa Department of Environmental Health, Rollins School of Public Health, Emory University, Atlanta, GA, USA.
¹⁵ Department of Population and Public Health Sciences, University of Southern California, Los Angeles, CA, USA.
¹⁶ Department of Population, Family and Reproductive Health, Johns Hopkins University Bloomberg School of Public Health, Baltimore, MD, USA.
¹⁷ Departments of Psychiatry, Psychology, and Clinical and Translational Science, University of Pittsburgh, Pittsburgh, PA, USA.
¹⁸ Department of Neurological Sciences and Pediatrics, University of Vermont School of Medicine, Burlington, VT, USA.
¹⁹ Department of Epidemiology, Geisel School of Medicine, Dartmouth College, Hanover, NH, USA.
²⁰ Department of Pediatrics, Brown University, Providence, RI, USA.
²¹ Department of Epidemiology, Johns Hopkins University Bloomberg School of Public Health, Baltimore, MD, USA.
²² AJ Drexel Autism Institute, Drexel University, Philadelphia, PA, USA.
²³ Avera Research Institute, Avera McKennan Hospital & University Health Center, Sioux Falls, SD, USA.
²⁴ Department of Pediatrics, Oregon Health & Science University, Portland, OR, USA.
²⁵ Channing Division of Network Medicine, Brigham and Women's Hospital, Boston, MA, USA; Harvard Medical School, Boston, MA, USA.
²⁶ Department of Environmental Science, Policy and Management and School of Public Health, University of California, Berkeley, Berkeley, CA, USA.
²⁷ Departments of Psychiatry, Neuroscience, and Obstetrics & Gynecology, University of Rochester, Rochester, NY, USA.
²⁸ Department of Public Health Sciences, University of California, Davis, Davis, CA, USA; MIND Institute, University of California, Davis, Davis, CA, USA.
²⁹ Department of Environmental and Occupational Health Sciences, University of Washington, Seattle, WA, USA; Department of Pediatrics, University of Washington, Seattle, WA, USA.
³⁰ Department of Obstetrics, Gynecology & Reproductive Sciences, University of California, San Francisco, San Francisco, CA, USA.

PMID: 41197644
PMCID: PMC12885132
DOI: 10.1016/j.lanplh.2025.101324

Wildfire-specific fine particulate matter and preterm birth: a US ECHO Cohort analysis

Allison R Sherris et al. Lancet Planet Health. 2025 Dec.

. 2025 Dec;9(12):101324.

doi: 10.1016/j.lanplh.2025.101324. Epub 2025 Nov 3.

Authors

Affiliations

¹ Department of Environmental and Occupational Health Sciences, University of Washington, Seattle, WA, USA. Electronic address: asherris@uw.edu.
² Department of Environmental and Occupational Health Sciences, University of Washington, Seattle, WA, USA.
³ Mailman School of Public Health, Columbia University, New York, NY, USA.
⁴ Department of Biostatistics, University of Washington, Seattle, WA, USA.
⁵ Department of Epidemiology, University of Washington, Seattle, WA, USA.
⁶ Department of Pediatrics, Avera Research Institute, University of South Dakota School of Medicine, Sioux Falls, SD, USA.
⁷ Department of Public Health Sciences, University of California, Davis, Davis, CA, USA.
⁸ Department of Epidemiology, University of Michigan, Ann Arbor, MI, USA.
⁹ Department of Emergency Medicine, Massachusetts General Hospital, Harvard Medical School, Boston, MA, USA.
¹⁰ Pediatrics and Environmental Medicine, Icahn School of Medicine at Mount Sinai, New York City, NY, USA.
¹¹ Prevention Science Institute, University of Oregon, Eugene, OR, USA.
¹² Division of Research, Kaiser Permanente Northern California, Pleasanton, CA, USA.
¹³ Lifecourse Epidemiology of Adiposity & Diabetes Center, Colorado School of Public Health, University of Colorado Anschutz Medical Campus, Aurora, CO, USA.
¹⁴ Gangarosa Department of Environmental Health, Rollins School of Public Health, Emory University, Atlanta, GA, USA.
¹⁵ Department of Population and Public Health Sciences, University of Southern California, Los Angeles, CA, USA.
¹⁶ Department of Population, Family and Reproductive Health, Johns Hopkins University Bloomberg School of Public Health, Baltimore, MD, USA.
¹⁷ Departments of Psychiatry, Psychology, and Clinical and Translational Science, University of Pittsburgh, Pittsburgh, PA, USA.
¹⁸ Department of Neurological Sciences and Pediatrics, University of Vermont School of Medicine, Burlington, VT, USA.
¹⁹ Department of Epidemiology, Geisel School of Medicine, Dartmouth College, Hanover, NH, USA.
²⁰ Department of Pediatrics, Brown University, Providence, RI, USA.
²¹ Department of Epidemiology, Johns Hopkins University Bloomberg School of Public Health, Baltimore, MD, USA.
²² AJ Drexel Autism Institute, Drexel University, Philadelphia, PA, USA.
²³ Avera Research Institute, Avera McKennan Hospital & University Health Center, Sioux Falls, SD, USA.
²⁴ Department of Pediatrics, Oregon Health & Science University, Portland, OR, USA.
²⁵ Channing Division of Network Medicine, Brigham and Women's Hospital, Boston, MA, USA; Harvard Medical School, Boston, MA, USA.
²⁶ Department of Environmental Science, Policy and Management and School of Public Health, University of California, Berkeley, Berkeley, CA, USA.
²⁷ Departments of Psychiatry, Neuroscience, and Obstetrics & Gynecology, University of Rochester, Rochester, NY, USA.
²⁸ Department of Public Health Sciences, University of California, Davis, Davis, CA, USA; MIND Institute, University of California, Davis, Davis, CA, USA.
²⁹ Department of Environmental and Occupational Health Sciences, University of Washington, Seattle, WA, USA; Department of Pediatrics, University of Washington, Seattle, WA, USA.
³⁰ Department of Obstetrics, Gynecology & Reproductive Sciences, University of California, San Francisco, San Francisco, CA, USA.

PMID: 41197644
PMCID: PMC12885132
DOI: 10.1016/j.lanplh.2025.101324

Abstract

Background: Exposure to PM_2·5 from wildfire smoke during pregnancy has been implicated as a risk factor for preterm birth. We investigated this association in the prospective nationwide US Environmental Influences on Child Health Outcomes (ECHO) Cohort, focusing on prenatal wildfire PM_2·5 exposure intensity, duration, and timing.

Methods: In this cohort analysis, we included live singleton births recorded in the ECHO Cohort with available data on gestational age at birth and birthweight and dates of conception between Jan 1, 2006, and March 20, 2020. Census tract-level estimates of daily mean wildfire-derived PM_2·5 for the years 2006-20 from a previous machine learning model were linked to residential address history. We calculated the mean concentration of daily wildfire PM_2·5, days with wildfire PM_2·5 (>0, ≥2·5, ≥5·0, and ≥10·0 μg/m³; termed smoke days) and consecutive smoke days (2, 3, or ≥4 days; termed smoke waves) above the prespecified concentration thresholds across pregnancy. Associations of cumlative pregnancy wildfire PM_2·5 exposure with preterm birth (delivery before 37 weeks of gestation) were analysed by adjusted pooled logistic regression in the nationwide ECHO sample and in the US West census region. Associations between smoke days in gestational weeks 0-35 and preterm birth were evaluated by logistic regression in the national sample.

Findings: We included 20 034 births from 30 ECHO Cohort study sites, with residences during pregnancy in all 48 contiguous US states and the District of Columbia. 1687 (8·4%) of the 20 034 infants were preterm. The mean daily wildfire PM_2·5 concentration during pregnancy was 0·36 μg/m³ (SD 0·46), with exposure to a mean of 22·2 smoke days (SD 16·6) of any wildfire PM_2·5 concentration (>0 μg/m³). Estimates of association between wildfire PM_2·5 exposure metrics and preterm birth included the null in nationwide analyses; whereas, in the US West sample (N=5807), we estimated increased odds of preterm birth associated with mean daily wildfire PM_2·5 (odds ratio [OR] 1·139 per 1-μg/m³ increase [95% CI 1·001-1·296]), exposure to smoke days with a wildfire PM_2·5 concentration of 5·0 μg/m³ or greater (OR 1·018 per additional smoke day [1·003-1·032]) and 10·0 μg/m³ or greater (OR 1·030 [1·006-1·054]), and exposure to ≥4-day smoke waves of 5·0 μg/m³ or greater (OR 1·185 per additional smoke wave [1·044-1·347]) and 10·0 μg/m³ or greater (OR 1·232 [1·029-1·475]). At the national level, by week of gestation, associations with preterm birth were observed in mid-pregnancy for smoke days with wildfire PM_2·5 concentrations above 0 μg/m³, of 2·5 μg/m³ or greater, and of 5·0 μg/m³ or greater, and in late pregnancy for smoke days of 10·0 μg/m³ or greater.

Interpretation: In a prospective cohort, we observed increased odds of preterm birth associated with wildfire PM_2·5 exposure in the western USA, with findings suggesting an exposure-response relationship for increasing exposure intensity and duration. Preterm birth was also associated with exposure to smoke days in mid-to-late pregnancy at the national level. For practice and policy, these findings support the need for public health interventions aimed at reducing exposure to wildfire smoke during pregnancy.

Funding: ECHO Program, US National Institutes of Health Office of the Director.

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Conflict of interest statement

Declaration of interests AEH was a member of a data safety and monitoring board for a treatment trial of blood pressure management at the University of Pittsburgh. ARS consulted for UNICEF on an analysis of child exposure to pesticides. CJK received an honorarium from Kaiser Permanente to present for paediatricians on wildfire smoke and child health, and received an honorarium and travel support from California Chapter 2 of the American Academy of Pediatrics to present on provider medical education related to air pollution and child health. CTM was chair of a data safety and monitoring board for a US National Institutes of Health (NIH) study, Safety of Sildenafil in Premature Infants with Severe Bronchopulmonary Dysplasia (SILDI-SAFE), and member of a data safety and monitoring board for the Pragmatic Research on Diuretic Management in Early BPD (PRIMED) Study. CTM also received annual fees and royalties as a peer reviewer for UpToDate, and honoraria for lectures including at an Endowed Lectureship at the University of Illinois in March, 2024, the Vermont Oxford Hot Topics Meeting in December, 2024, and the Mednax Center for Research, Education, Quality and Safety Annual Conference for Neonatology in February, 2025. DH was a member of an advisory committee for the Targeting Environmental Neurodevelopmental Risks Project. JA served on the Avera Health Institutional Review Board. RJS has received funding support from the Bia-Echo Foundation. RJS also consults for Linus Technology, and consulted for the Beasley Law Firm until March, 2023. RJS also received travel support to serve on the Observational Study Monitoring Board for the Healthy Brain and Child Development (HBCD) Study, to present at the BC Lung Foundation Air Quality & Health Workshop 2025 (April, 2025), to present at the Japan Society of Endocrine Disruptors Research Meeting (December, 2024), to present at the Society for Birth Defects Research and Prevention 64th Annual Meeting (June, 2024), and to present at the 35th Annual Meeting of the Organization of Teratology Information Specialists (June, 2023). All other authors declare no competing interests.

Figures

Figure 1:. Approximate jittered locations of the first recorded residential address of pregnant individuals within the four US census regions and number of smoke days (wildfire PM_2·5 >0 μg/m³) during pregnancy (N=20 034 births)
*The overall mean number of smoke days was 22·2 (SD 16·6).

Figure 2:. Associations between exposure to cumulative mean daily wildfire PM_2·5, cumulative smoke days, and cumulative smoke waves during pregnancy and preterm birth in the nationwide study sample (N=20 034 births; A) and the US West study sample (N=5807 births; B)
ORs are reported per 1-μg/m³ increase in mean daily wildfire PM_2·5, per additional smoke day, and per additional smoke wave. Associations were analysed with pooled logistic regression adjusted for the pregnant individual’s age at delivery (spline with 3 degrees of freedom), race, and Hispanic ethnicity, infant sex, census tract (neighbourhood) poverty rate during pregnancy, season of conception, infant birth year (spline with 4 degrees of freedom), and spatial splines (10 degrees of freedom), with a random intercept for cohort study site. Note that scales on y-axes differ between plots. OR=odds ratio.

**Figure 3:. Associations between smoke days of varying intensity by week of gestation and preterm birth**
ORs are reported per additional smoke day. Associations were analysed with logistic regression adjusted for the pregnant individual’s age at delivery (spline with 3 degrees of freedom), race, and Hispanic ethnicity, infant sex, census tract (neighbourhood) poverty rate during pregnancy, season of conception, infant birth year (spline with 4 degrees of freedom), and spatial splines (10 degrees of freedom), with a random intercept for cohort study site. OR=odds ratio.

**Figure 4:. Effect modification of the relationship between cumulative wildfire PM_2·5 exposure metrics and preterm birth**
ORs are reported per 1-μg/m³ increase in mean daily wildfire PM_2·5 and per additional smoke day. Effect estimates were derived from stratified pooled logistic regression models. p values were obtained from multiplicative interaction terms for binary modifiers and from Wald χ² tests of interaction coefficients for categorical modifiers. Note that scales on x-axes differ between plots. OR=odds ratio. *Race categories with small available sample sizes (American Indian or Native Alaskan, more than one race, and Other race) were omitted from effect modification analyses.

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References

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Wildfire-specific fine particulate matter and preterm birth: a US ECHO Cohort analysis

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Wildfire-specific fine particulate matter and preterm birth: a US ECHO Cohort analysis

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