Association of Long-term Exposure to Airborne Particulate Matter of 1 μm or Less With Preterm Birth in China

Abstract

<p class="first" id="d1594249e582">This national cohort study of more than 1.3 million births in China from December 1, 2013, to November 30, 2014, assesses the association of concentration of airborne particulate matter of 1 μm or less with the risk of preterm birth and identifies subgroups of pregnant women who may be vulnerable. </p><div class="section"> <a class="named-anchor" id="ab-poi170101-1"> <!-- named anchor --> </a> <h5 class="section-title" id="d1594249e588">Question</h5> <p id="d1594249e590">Is the concentration of airborne particulate matter with a median diameter of 1 μm or less (PM ₁) associated with the risk of preterm birth in China? </p> </div><div class="section"> <a class="named-anchor" id="ab-poi170101-2"> <!-- named anchor --> </a> <h5 class="section-title" id="d1594249e596">Findings</h5> <p id="d1594249e598">This national cohort study of more than 1.3 million births found that increases in PM ₁ concentration of 10 μg/m ³ during the entire pregnancy as well as at each trimester were significantly associated with an increased risk of preterm birth. </p> </div><div class="section"> <a class="named-anchor" id="ab-poi170101-3"> <!-- named anchor --> </a> <h5 class="section-title" id="d1594249e607">Meaning</h5> <p id="d1594249e609">Exposure to PM ₁ air pollution is associated with an increased risk of preterm birth, and control measures to reduce PM ₁ air pollution may lower the future incidence of preterm birth. </p> </div><div class="section"> <a class="named-anchor" id="ab-poi170101-4"> <!-- named anchor --> </a> <h5 class="section-title" id="d1594249e620">Importance</h5> <p id="d1594249e622">Airborne particulate matter pollution has been associated with preterm birth (PTB) in some studies. However, most of these studies assessed only populations living near monitoring stations, and the association of airborne particulate matter having a median diameter of 1 μm or less (PM ₁) with PTB has not been studied. </p> </div><div class="section"> <a class="named-anchor" id="ab-poi170101-5"> <!-- named anchor --> </a> <h5 class="section-title" id="d1594249e628">Objective</h5> <p id="d1594249e630">To evaluate whether PM ₁ concentrations are associated with the risk of PTB. </p> </div><div class="section"> <a class="named-anchor" id="ab-poi170101-6"> <!-- named anchor --> </a> <h5 class="section-title" id="d1594249e636">Design, Setting, and Participants</h5> <p id="d1594249e638">This national cohort study used National Free Preconception Health Examination Project data collected in 324 of 344 prefecture-level cities from 30 provinces of mainland China. In total, 1 300 342 healthy singleton pregnancies were included from women who were in labor from December 1, 2013, through November 30, 2014. Data analysis was conducted between December 1, 2016, and April 1, 2017. </p> </div><div class="section"> <a class="named-anchor" id="ab-poi170101-7"> <!-- named anchor --> </a> <h5 class="section-title" id="d1594249e641">Exposures</h5> <p id="d1594249e643">Predicted weekly PM ₁ concentration data collected using satellite remote sensing, meteorologic, and land use information matched with the home addresses of pregnant women. </p> </div><div class="section"> <a class="named-anchor" id="ab-poi170101-8"> <!-- named anchor --> </a> <h5 class="section-title" id="d1594249e649">Main Outcomes and Measures</h5> <p id="d1594249e651">Preterm birth (&lt;37 gestational weeks). Gestational age was assessed using the time since the first day of the last menstrual period. Cox proportional hazards regression analysis was used to examine the associations between trimester-specific PM ₁ concentrations and PTB after controlling for temperature, seasonality, spatial variation, and individual covariates. </p> </div><div class="section"> <a class="named-anchor" id="ab-poi170101-9"> <!-- named anchor --> </a> <h5 class="section-title" id="d1594249e657">Results</h5> <p id="d1594249e659">Of the 1 300 342 singleton live births at the gestational age of 20 to 45 weeks included in this study, 104 585 (8.0%) were preterm. In fully adjusted models, a PM ₁ concentration increase of 10 μg/m ³ over the entire pregnancy was significantly associated with increased risk of PTB (hazard ratio [HR], 1.09; 95% CI, 1.09-1.10), very PTB as defined as gestational age from 28 through 31 weeks (HR, 1.20; 95% CI, 1.18-1.23), and extremely PTB as defined as 20 through 27 weeks’ gestation (HR, 1.29; 95% CI, 1.25-1.34). Pregnant women who were older (30-50 years) at conception (HR, 1.13; 95% CI, 1.11-1.14), were overweight before pregnancy (HR, 1.13; 95% CI, 1.11-1.15), had a rural household registration (HR, 1.09; 95% CI, 1.09-1.10), worked as farmers (HR, 1.10; 95% CI, 1.09-1.11), and conceived in autumn (HR, 1.48; 95% CI, 1.46-1.50) appeared to be more sensitive to PM ₁ exposure than their counterparts. </p> </div><div class="section"> <a class="named-anchor" id="ab-poi170101-10"> <!-- named anchor --> </a> <h5 class="section-title" id="d1594249e671">Conclusions and Relevance</h5> <p id="d1594249e673">Results from this national cohort study examining more than 1.3 million births indicated that exposure to PM ₁ air pollution was associated with an increased risk of PTB in China. These findings will provide evidence to inform future research studies, public health interventions, and environmental policies. </p> </div>