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Wildfire smoke exposure linked to premature births

Scientists have long been aware of the detrimental effects of poor air quality on people’s health. In pregnant women, previous research has shown that air pollution, such as smog, can lead to a series of adverse outcomes, including preterm birth (PTB, defined as delivery before the 37th week of pregnancy), which is one of the leading causes of infant mortality in the United States.

Now, a study led by Stanford University has found that exposure to another type of potentially even more dangerous pollutant, wildfire smoke, increases a pregnant woman’s chances of going into labor prematurely, a phenomenon known as spontaneous preterm birth.

Since wildfire smoke contains microscopic particles that can enter deep into the lungs, it can worsen pre-existing health conditions such as asthma or heart disease. These extremely fine particles can also travel for hundreds or even thousands of miles from their point of origin, thus posing significant threats for a large number of people.

To assess wildfire smoke’s impact on pregnancy, the scientists reviewed birth certificates and hospital delivery data from 2007 to 2012 of over 2.5 million pregnant women in California. Then, they compared this data with daily estimates of wildfire smoke intensity by zip code.

The analysis revealed that four weeks prior to conception through the first 20 weeks of pregnancy, 86 percent of pregnant women were exposed to at least one day of wildfire smoke, with an average exposure period of 7.5 days. According to the data, wildfire smoke was significantly linked to spontaneous preterm birth, with each additional day of exposure slightly increasing the odds of delivering an infant prematurely.

“Wildfires lead to acute and abrupt changes in air quality. And some emerging evidence suggests that wildfire smoke could be worse for your health than other types of pollutants,” said study lead author Anne Waldrop, an expert in Maternal-Fetal Medicine at Stanford. 

“So, even as we work to decrease other forms of air pollution, with wildfires becoming more frequent, more intense, and happening on a much larger scale, exposure to wildfire smoke is a serious public health problem, especially for vulnerable populations like pregnant people,” she concluded. 

The study is published in the American Journal of Obstetrics & Gynecology. 


By Andrei Ionescu, Staff Writer

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