Adverse Birth Outcomes Related to NO2 and PM Exposure: European Systematic Review and Meta-Analysis

Abstract

There is a growing number of international studies on the association between ambient air pollution and adverse pregnancy outcomes, and this systematic review and meta-analysis has been conducted focusing on European countries, to assess the crucial public health issue of this suspected association on this geographical area. A systematic literature search (based on Preferred Reporting Items for Systematic reviews and Meta-Analyses, PRISMA, guidelines) has been performed on all European epidemiological studies published up until 1 April 2020, on the association between maternal exposure during pregnancy to nitrogen dioxide (NO₂) or particular matter (PM) and the risk of adverse birth outcomes, including: low birth weight (LBW) and preterm birth (PTB). Fourteen articles were included in the systematic review and nine of them were included in the meta-analysis. Our meta-analysis was conducted for 2 combinations of NO₂ exposure related to birth weight and PTB. Our systematic review revealed that risk of LBW increases with the increase of air pollution exposure (including PM₁₀, PM_2.5 and NO₂) during the whole pregnancy. Our meta-analysis found that birth weight decreases with NO₂ increase (pooled beta = -13.63, 95% confidence interval (CI) (-28.03, 0.77)) and the risk of PTB increase for 10 µg/m3 increase in NO₂ (pooled odds ratio (OR) = 1.07, 95% CI (0.90, 1.28)). However, the results were not statistically significant. Our finding support the main international results, suggesting that increased air pollution exposure during pregnancy might contribute to adverse birth outcomes, especially LBW. This body of evidence has limitations that impede the formulation of firm conclusions. Further studies, well-focused on European countries, are called to resolve the limitations which could affect the strength of association such as: the exposure assessment, the critical windows of exposure during pregnancy, and the definition of adverse birth outcomes. This analysis of limitations of the current body of research could be used as a baseline for further studies and may serve as basis for reflection for research agenda improvements.

Keywords: NO2; PM; air pollution; birth weight; exposure; low birth weight; meta-analysis; preterm birth; systematic review.

Figure A1

Risk of birth outcome for air pollutant exposure during overall pregnancy.

Figure A2

Risk of birth outcome for air pollutant exposure during first trimester.

Figure A3

Risk of birth outcome for air pollutant exposure during second trimester.

Figure A4

Risk of birth outcome for air pollutant exposure during third trimester.

Figure 1

Preferred Reporting Items for Systematic reviews and Meta-Analyses (PRISMA) 2009 Flow Diagram. From: Moher D, Liberati A, Tetzlaff J, Altman DG, The PRISMA Group (2009). Preferred Reporting Items for Systematic Reviews and Meta-Analyses: The PRISMA Statement. PLoS Med 6: e1000097. doi:10.1371/journal.pmed1000097 [63].

Figure 2

Risk of birth outcome for NO₂ exposure during different windows of exposure during pregnancy.

Figure 3

Risk of birth outcome for PM₁₀ exposure during different windows of exposure during pregnancy.

Figure 4

Risk of birth outcome for PM_2.5 exposure during different windows of exposure during pregnancy.

Figure 5

Association between birth weight and NO₂ exposure during the first trimester of pregnancy.

Figure 6

Association between birth weight and NO₂ exposure during the second trimester of pregnancy.

Figure 7

Association between birth weight and NO₂ exposure during the third trimester of pregnancy.

Figure 8

Association between birth weight and NO₂ exposure during the entire pregnancy.

Figure 9

Association between preterm birth and NO₂ exposure during the entire pregnancy.