Ambient and household PM2.5 pollution and adverse perinatal outcomes: A meta-regression and analysis of attributable global burden for 204 countries and territories

Abstract

Background: Particulate matter <2.5 micrometer (PM2.5) is associated with adverse perinatal outcomes, but the impact on disease burden mediated by this pathway has not previously been included in the Global Burden of Disease (GBD), Mortality, Injuries, and Risk Factors studies. We estimated the global burden of low birth weight (LBW) and preterm birth (PTB) and impacts on reduced birth weight and gestational age (GA), attributable to ambient and household PM2.5 pollution in 2019.

Methods and findings: We searched PubMed, Embase, and Web of Science for peer-reviewed articles in English. Study quality was assessed using 2 tools: (1) Agency for Healthcare Research and Quality checklist; and (2) National Institute of Environmental Health Sciences (NIEHS) risk of bias questions. We conducted a meta-regression (MR) to quantify the risk of PM2.5 on birth weight and GA. The MR, based on a systematic review (SR) of articles published through April 4, 2021, and resulting uncertainty intervals (UIs) accounted for unexplained between-study heterogeneity. Separate nonlinear relationships relating exposure to risk were generated for each outcome and applied in the burden estimation. The MR included 44, 40, and 40 birth weight, LBW, and PTB studies, respectively. Majority of the studies were of retrospective cohort design and primarily from North America, Europe, and Australia. A few recent studies were from China, India, sub-Saharan Africa, and South America. Pooled estimates indicated 22 grams (95% UI: 12, 32) lower birth weight, 11% greater risk of LBW (1.11, 95% UI: 1.07, 1.16), and 12% greater risk of PTB (1.12, 95% UI: 1.06, 1.19), per 10 μg/m3 increment in ambient PM2.5. We estimated a global population-weighted mean lowering of 89 grams (95% UI: 88, 89) of birth weight and 3.4 weeks (95% UI: 3.4, 3.4) of GA in 2019, attributable to total PM2.5. Globally, an estimated 15.6% (95% UI: 15.6, 15.7) of all LBW and 35.7% (95% UI: 35.6, 35.9) of all PTB infants were attributable to total PM2.5, equivalent to 2,761,720 (95% UI: 2,746,713 to 2,776,722) and 5,870,103 (95% UI: 5,848,046 to 5,892,166) infants in 2019, respectively. About one-third of the total PM2.5 burden for LBW and PTB could be attributable to ambient exposure, with household air pollution (HAP) dominating in low-income countries. The findings should be viewed in light of some limitations such as heterogeneity between studies including size, exposure levels, exposure assessment method, and adjustment for confounding. Furthermore, studies did not separate the direct effect of PM2.5 on birth weight from that mediated through GA. As a consequence, the pooled risk estimates in the MR and likewise the global burden may have been underestimated.

Conclusions: Ambient and household PM2.5 were associated with reduced birth weight and GA, which are, in turn, associated with neonatal and infant mortality, particularly in low- and middle-income countries.

Fig 1. The annual average ambient (a) and household (b) PM_2.5 concentrations (μg/m³) in 204 countries and territories for 2019.

The box plots in the inset show the super regional distributions. Note: The red horizontal line in the overall plots represent the global median, and those within the boxes are the GBD 2019 super regional medians. The boxplots are arranged in the same order as the super regions in the overall plot. GBD, Global Burden of Disease, Injuries, and Risk Factors; PM_2.5, particulate matter <2.5 micrometer.

Fig 2. The estimated global reduction in population-weighted birth weight (grams) attributable to total PM_2.5 air pollution (from ambient and household sources) for 2019.

PM_2.5, particulate matter <2.5 micrometer.

Fig 3. The estimated global reduction in population-weighted gestational age (weeks) attributable to total PM_2.5 air pollution (from ambient and household sources) for 2019.

The mapping function or the base layers for Figs 2 and 3 were obtained from this source: http://www.fao.org/geonetwork/srv/en/metadata.show?id=12691. PM_2.5, particulate matter <2.5 micrometer.

Fig 4. The estimated global burden [PAFs (a) and PANs (b)] of low birth weight attributable to total PM_2.5 air pollution (from ambient and household sources) for 2019.

PAF, population attributable fraction; PAN, population attributable number; PM_2.5, particulate matter <2.5 micrometer.

Fig 5. The estimated global burden [PAFs (a) and PANs (b)] of preterm birth attributable to total PM_2.5 air pollution (from ambient and household sources) for 2019.

The mapping function or the base layers for Figs 4 and 5 were obtained from this source: https://data.apps.fao.org/map/catalog/srv/eng/catalog.search#/metadata/9c35ba10-5649-41c8-bdfc-eb78e9e65654. PAF, population attributable fraction; PAN, population attributable number; PM_2.5, particulate matter <2.5 micrometer.