The International Collaboration on Air Pollution and Pregnancy Outcomes: initial results

Abstract

Background: The findings of prior studies of air pollution effects on adverse birth outcomes are difficult to synthesize because of differences in study design.

Objectives: The International Collaboration on Air Pollution and Pregnancy Outcomes was formed to understand how differences in research methods contribute to variations in findings. We initiated a feasibility study to a) assess the ability of geographically diverse research groups to analyze their data sets using a common protocol and b) perform location-specific analyses of air pollution effects on birth weight using a standardized statistical approach.

Methods: Fourteen research groups from nine countries participated. We developed a protocol to estimate odds ratios (ORs) for the association between particulate matter ≤ 10 μm in aerodynamic diameter (PM₁₀) and low birth weight (LBW) among term births, adjusted first for socioeconomic status (SES) and second for additional location-specific variables.

Results: Among locations with data for the PM₁₀ analysis, ORs estimating the relative risk of term LBW associated with a 10-μg/m³ increase in average PM₁₀ concentration during pregnancy, adjusted for SES, ranged from 0.63 [95% confidence interval (CI), 0.30-1.35] for the Netherlands to 1.15 (95% CI, 0.61-2.18) for Vancouver, with six research groups reporting statistically significant adverse associations. We found evidence of statistically significant heterogeneity in estimated effects among locations.

Conclusions: Variability in PM₁₀-LBW relationships among study locations remained despite use of a common statistical approach. A more detailed meta-analysis and use of more complex protocols for future analysis may uncover reasons for heterogeneity across locations. However, our findings confirm the potential for a diverse group of researchers to analyze their data in a standardized way to improve understanding of air pollution effects on birth outcomes.

Figure 1

ORs (95% CIs) for LBW among term births in association with a 10‑μg/m³ increase in estimated average PM₁₀, or black smoke (PAMPER), concentration during the entire pregnancy, adjusted for SES (model 1), by study.

Figure 2

ORs (95% CIs) for LBW among term births in association with a 10‑μg/m³ increase in estimated average PM₁₀, or black smoke (PAMPER), concentration during the entire pregnancy, adjusted for SES and study-specific variables (model 2), by study.

Figure 3

Change in mean birth weight (95% CIs) among term births in association with a 10‑μg/m³ increase in estimated average PM₁₀, or black smoke (PAMPER), concentration during the entire pregnancy, adjusted for SES, by study.

Figure 4

ORs (95% CIs) for LBW among term births in association with a 10‑μg/m³ increase in estimated average PM_2.5 concentration during the entire pregnancy, adjusted for SES, by study. Results for the Vancouver study are from two different PM_2.5 estimation methods, LUR and IDW of monitor measurements (see "Methods").