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Antenatal wildfire smoke exposure and preterm birth phenotypes: A retrospective cohort study
Anne R Waldrop1, Yair J Blumenfeld1, Jonathan A Mayo1
1Division of Maternal Fetal Medicine & Obstetrics, Department of Obstetrics & Gynecology, Stanford University, Stanford, California.
Background:
Novel evidence suggests an association of wildfire smoke exposure with preterm birth (PTB). However, the mechanism and exposure timing of this association are poorly understood.
Objective:
We estimate the association of wildfire smoke on PTB phenotypes (spontaneous PTB [sPTB] and medically indicated PTB [mPTB]) as well as hypertensive disorders of pregnancy (HDP).
Study Design:
Birth cohort data from singleton livebirths in California from 2007 to 2012 were combined with daily zip code-level estimates of wildfire smoke intensity. Satellite-based estimates of wildfire smoke plume boundaries and high-resolution gridded estimates of surface particulate matter 2.5 (PM2.5) concentrations were used to calculate smoke exposure from 4 weeks preconception through gestational week 20. The two primary exposures were (1) wildfire smoke exposure at distinct gestational ages and (2) concentration of wildfire smoke exposure. Logistic regression models assessed associations between the number of wildfire smoke-exposed days and PTB phenotypes. HDP were also assessed as an outcome, given their major contribution to mPTB. Four primary outcomes were used: (1) overall PTB (<37 weeks), (2) sPTB, (3) mPTB, and (4) HDP.
Results:
Of 2,548,347 eligible pregnant individuals, 86% were exposed to at least 1 day of wildfire smoke of any PM2.5 intensity during the exposure period. Wildfire smoke of any intensity was significantly associated with sPTB during the exposure period (odds ratios [OR] [95% confidence intervals (CI)]: 1.003 [1.0021, 1.0039]). Each additional day of smoke exposure conferred 0.3% increased odds of sPTB. We did not observe an association of wildfire smoke with HDP. Only smoke exposure of any intensity between 14 and 20 weeks was associated with increased odds of mPTB OR CI (95%) (1.0038 [1.0008, 1.0069]). Wildfire smoke exposure of any intensity in the gestational period of smoke exposure was associated in increased odds of all PTB, except for the preconception period.
Conclusions:
Our study found an association of wildfire smoke exposure with PTB, which was largely driven by sPTB.
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