Pooled Analysis of Preterm Birth and Air Pollution

A pooled analysis or meta-analysis was not performed because of the heterogeneity of the study populations across geographic locations and the heterogeneity of exposures (ie, PM_2.5 from vehicle traffic and wildfires). The review presented the primary findings in summary of evidence tables for each key question and tabulated the preponderance of evidence that found significant associations (ie, 19 of 24 studies on preterm birth and air pollution found a significant association). The overall number of births were included in the review, and the Table lists the number of births reviewed for each key question, and the mean (SD) births among these studies. This was presented to highlight the large populations being studied that provided credence to the significant findings. The degree of risk was identified for significant associations as a range with median. These data were tabulated and calculated with an Excel spreadsheet (Microsoft).