effects of air pollution

In Southwestern Ontario, researchers studied if environmental factors are associated with adverse birth outcomes such as low birth weight and preterm birth.


Adverse birth outcomes can lead to disease and mortality. Within developing countries, the percentage of babies born with low birth weight is 16.5%, and in developed countries, that number is 7%. There have been some studies that have seen links of adverse birth outcomes to air pollution, while others have not.

A cohort study published by Environmental Research included data on pregnant women and their live births. The women in this study gave birth between February 2009 and February 2014. There were a total number of 25,263 births.

The researchers collected the data from the London Health Sciences Centre (LHSC). Each woman’s postal code was known so that researchers would examine the environmental status where births took place. Researchers used logistic regression to examine the possible factors.

Sulphur dioxide in the air was the main cause of preterm births and low birth weights

Researchers found that out of all the births, 7,5% were preterm births and just 5.7% had low birth weights. They found that the presence of sulphur dioxide in the air was the main cause of these results.

The women were at an increased the risk of an LBW infant by 3.4 times and two-time risk for a pre-term-birth infant – this is due to a 1-parts per billion (ppb) growth of sulphur dioxide within the air. Even though 1 ppb does not seem substantial, the study highlights that a one-unit increase impacts air pollution significantly.

Furthermore, being underweight and having thyroid problems pre-pregnancy (among other factors), poses a higher risk of low birth weights and preterm birth. Marijuana and tobacco use were associated with low birth weight but were not associated with preterm birth.

It is possible that having a lower socioeconomic status may put pregnant women at risk of having a pre-term-birth or low-birth-weight infant. Most studies show that recent immigration leads to a decrease in chances of low-birth-weight and/or pre-term birth. This is because immigrants usually arrive in Canada very healthy.

A limitation of this study is that the postal code where the participants lived may not have been the exact place they gave birth. This study was extremely strong due to the high participant numbers.

Pregnant women should visit clean-air areas

Pregnant women are highly encouraged to visit clean-air areas such as open parks, forests, and other nature-filled areas. After looking at the effects of air pollution, researchers suggest further studies to become more informed on this topic.

Written by Laura Laroche, HBASc, Medical Writer


  1. Seabrook, Jamie, A, et al. “Geospatial Analyses of Adverse Birth Outcomes in Southwestern Ontario: Examining the Impact of Environmental Factors”. Environmental Research. Apr. 4 2019. 1-9. Online.
  2. Strong link between air pollution in Southwestern Ontario and adverse birth outcomes. 2019, https://www.eurekalert.org/pub_releases/2019-04/lhri-slb040319.php, assessed Apr. 4 2019.
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