Exposure to wildfire smoke could be associated with thousands of additional preterm births, a new study has found.
In a paper published this month in Environmental Research, a team of researchers at Stanford University estimated that there were nearly 7,000 extra preterm births associated with exposure to wildfire smoke between 2007 and 2012 in California, or nearly 4 percent of all the preterm births during those years.
“We knew air pollution increased the risk of preterm birth, but this new work highlights the importance of pollutants associated with wildfire smoke, which might be different from other sources of air pollution, and are becoming more of an issue with climate change,” said Lara Cushing, an environmental health scientist at the U.C.L.A. Fielding School of Public Health who was not involved with the research.
Wildfire smoke contains high levels of the smallest, most dangerous type of soot. Exposure to these particles, known as PM 2.5, is believed to cause inflammation within the body, putting strain on the immune system and decreasing blood flow to organs, including the placenta, which can trigger contractions and delivery.
Preterm births, or births that occur between 20 and 36 weeks of pregnancy, are associated with a range of developmental delays, respiratory, vision, and hearing problems, and can contribute to chronic diseases into adulthood. They account for 10 percent of all births in the United States and are one of the leading causes of infant mortality.
Researchers found that a week of exposure was associated with a 3 percent increased risk of preterm birth. In 2008, the worst smoke year in their study period, the researchers found that wildfire smoke exposure was associated with more than 6 percent of all preterm births in California.
Wildfires have intensified in the years since. “2020 was about two and a half times as bad as 2008. And four of the last five years have been worse smoke than 2008,” said Sam Heft-Neal, a research scholar at the Stanford University Center on Food Security and the Environment and the lead author of the study.
The findings build on a well-established link between air pollution and adverse fetal health outcomes.
To arrive at their conclusion, the researchers used satellite data of smoke plumes to identify the locations and days affected by wildfires. They paired those readings with ground-level PM 2.5 data and California birth records.
Wildfire smoke may contribute up to half of the PM 2.5 in some parts of the western United States. It is so far unclear whether wildfire smoke is more or less toxic than particulate matter from diesel combustion or power plants.
Rupa Basu, the chief of air and climate epidemiology at the California Environmental Protection Agency’s Office of Environmental Health Hazard Assessment, said that in addition to thinking about the effects of wildfire exposure on infant health, the effects on mothers must also be considered.
“There’s mental health issues that go along with the stress of having a premature infant,” said Dr. Basu, who has studied the effects of climate change and environment on pregnant women and noted that preterm births also can happen more rapidly and spontaneously than expected, adding to the potential for trauma.