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Wildfires pose health risk to pregnancy, experts warn. Here’s what to know



Amid the ongoing wildfires engulfing regions of Canada, experts are warning pregnant people about the health impacts of breathing smoke and the potential risks it poses to both maternal and fetal well-being.

From British Columbia to the Atlantic provinces, wildfire smoke continues to billow in the sky, causing poor air quality alerts for many regions, even reaching as far south as North and South Carolina in the United States on Wednesday.

And for vulnerable populations, such as pregnant people, wildfire smoke can pose a greater risk than the average person.

“The global evidence really suggests that if people are inhaling this wildfire smoke, it may impact birth outcomes,” said Matthew Adams, an associate professor of geography and the department of geography, geomatics and environment at the University of Toronto, Mississauga.

Wildfire season typically runs from early April to late October, according to Environment Canada.


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As a wildfire burns through forests and grasslands, it produces dense smoke that can be a major source of toxic air pollutants, which can contain fine particles known as PM 2.5 (that are not visible to the human eye). The fine particles have the ability to penetrate deep into people’s lungs and bloodstream, sometimes leading to serious health effects.

“A pregnant woman’s blood will flow through her placenta, and then these particles can mix with the baby’s blood and then get into the baby’s organs and the baby’s lungs,” explained Dr. David Olson, a professor of obstetrics and gynecology at the University of Alberta.

“And it can set up an inflammatory reaction in the baby. And the baby isn’t as well buffered against inflammatory mediators as the mother is. So then there are all kinds of adverse outcomes,” he said.


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This includes potential pre-term births, miscarriages, and growth impairment of organs, he said.

Wildfire smoke can also have a detrimental effect on the oxygen supply for the baby, Olson warned. This is because the smoke can contain harmful substances such as carbon monoxide, carbon dioxide and sulphur dioxide that interact with red blood cells and reduce the amount of oxygen that can be transferred from the mother to the baby.

This reduction in oxygen supply can potentially lead to the birth of slightly smaller babies, he said.


Wildfire and birth outcomes

While research on the link between smoke inhalation during pregnancy and wildfires is limited, there have been emerging studies on the subject.

“There has been growing interest and concern about air pollution and low birth weight and other birth outcomes. And that’s been developing in the scientific literature. It’s never a for sure thing, but we definitely see strong associations,” Adams said.


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For example, Adams was a co-author of a 2022 study published in the Lancet Regional Health, looking at the birth weight following pregnancy wildfire smoke exposure in more than 1.5 million newborns in Brazil.

The researchers found that an increase of 100 wildfire records in Brazil was associated with an increase in low birth weight when the exposure occurred in the first trimester of pregnancy.

“Given that wildfire is a growing problem in several regions worldwide, especially in Brazil — a fire-prone region, the epidemiological evidence shown in our study should be of great concern to the public health community and policymakers,” the researchers concluded.

The findings out of Brazil are likely going to be the same in Canada, Adams argued.



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“The human body is going to be the same in Brazil as it is in Canada. So that exposure to wildfire smoke would unfortunately probably have very similar impacts,” he said. “We do see wildfires, in western Canada and eastern Canada right now. And it’s troubling.”


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Another study, published out of the Colorado School of Public Health in 2019, found a “significant positive association between exposure to wildfire smoke and gestational diabetes” during pregnancy. Exposure to wildfire smoke during the second trimester was also “positively associated with preterm birth,” the authors stated.

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There are also stress-included reactions pregnant people can have from wildfires, Olson said.

When pregnant people are advised to stay indoors to avoid inhaling wildfire smoke, it can impact them in various ways, such as experiencing feelings of isolation or enduring heightened stress due to the restrictions, he said.

And then there’s stress faced by those living in wildfires zones. Olsson explained that as many pregnant people may have to confront the possibility of losing their homes or being evacuated, it causes chronic stress during pregnancy can have significant implications.

High levels of prenatal stress exposure, particularly early in the pregnancy, have been shown to potentially negatively affect the brain development of the fetus.


How pregnant people can protect themselves from wildfires

Health Minister Jean-Yves Duclos on Wednesday advised vulnerable Canadians, such as those who are pregnant, to wear masks.


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“The situation is particularly critical for pregnant women, young children, seniors, those living with respiratory diseases and chronic conditions,” he said ahead of Wednesday’s Liberal caucus meeting.

“So the advice is to wear a mask if people want to do that,” he said. “That can protect against the inhalation of particles. Also to avoid going outside if that is possible. And if it’s needed, then to do it quickly and without strenuous effort. And to be mindful of local evidence regarding the quality of air.”

During wildfire season, Adams stressed the importance for pregnant people to prioritize their safety and use a high-efficiency particulate air filter at home, also known as a HEPA filter.



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“We know that the HEPA filter will filter out the particles that are being generated by the wildfire,” he said.


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Health Canada’s Air Quality Health Index is also a helpful tool, which shows regions with high pollutants levels and is particularly relevant for those vulnerable to air pollution, he added.

Olson recommends that pregnant people stay inside (if possible) with the windows and door shut, and to specifically wear an N95 mask or even a respirator.

“If you’re pregnant, be extra cautious,” he said. “Wear a mask, don’t go out for a long time and exercise indoors, if you can.”

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