November is Prematurity Awareness Month in the United States.  Prematurity has been increasing on a global level every year and more than 15 million babies are born before 37 weeks worldwide.  The impact of premature birth has significant costs financially, emotionally and health wise for babies, parents and society.  Currently, preterm birth in the United States carries an economic cost of $25 billion per year.

In the United States, the past decade has seen a considerable increase in wildfires, particularly across the western part of the country.  A study titled “Associations between wildfire smoke exposure during pregnancy and risk of preterm birth in California,” published earlier this year in the peer-reviewed journal  Environmental Research, found that wildfires may have caused more than 7,000 additional preterm births in California in the years 2007-2012.  This is more than 3.7% of all the births that occurred prior to 37 weeks during those years.  Premature births increase the risk of long term health problems including neurodevelopment delays, respiratory complications, gastrointestinal problems and even death in babies.

Research on the health concerns for populations exposed to wildfire smoke are ongoing, as the number of wildfires and the acreage that burns steadily increases year after year.  In 2020, California residents experienced a month of smoke levels that were classified in the range of unhealthy to hazardous as a result of the unprecedented number of wildfires in the state.  Wildfire smoke contains high levels of the smallest and deadliest type of particle pollution, known as PM 2.5. Much is still unknown about these types of fine particle pollution, but it is known that the toxic specks of particulate matter can embed deep in the lungs and pass into the bloodstream.

Researchers believe that there are a variety of reasons that wildfire smoke exposure increases preterm birth rates.  One possible cause is thought to be an inflammatory response in the pregnant parent that is triggered by the fine particles that are inhaled, which can cause premature labor.

With wildfires expected to continue to increase in size, duration and frequency in many parts of the Western United States due to climate change, human development and other factors, people can expect to be increasingly exposed to wildfire smoke and the number of preterm births that can be attributed to smoke exposure will increase.

Researchers used smoke plume satellite data and ground level fine particle pollution that was available from the National Oceanic and Atmospheric Administration (NOAA) and overlaid this data on top of over 2,600 zip codes in California.  Data from California birth records of singleton babies during the same period was retrieved.  After accounting for other factors known to influence preterm birth risk, such as temperature, baseline pollution exposure and the pregnant parent's age, income, race or ethnic background, researchers examined how patterns of preterm birth within each zip code changed when the number and intensity of smoke days rose above what is considered normal for that location.

Researchers found that “every additional day of smoke exposure during pregnancy raised the risk of preterm birth, regardless of race, ethnicity or income. And a full week of exposure translated to a 3.4 percent greater risk relative to a mother exposed to no wildfire smoke. Exposure to intense smoke during the second trimester -- between 14 and 26 weeks of pregnancy -- had the strongest impact, especially when smoke contributed more than 5 additional micrograms per cubic meter to daily PM 2.5 concentrations.”

There already had been a well established connection between particle pollution and adverse birth outcomes, including preterm birth, low birth weight and infant deaths. What made this study unusual is that it was one of the first studies to examine exposure timing.  Pregnant people, as part of those identified as vulnerable populations, should do whatever they can to reduce exposure to the smoke from wildfires whenever possible.

References

Heft-Neal, S., Driscoll, A., Yang, W., Shaw, G., & Burke, M. (2022). Associations between wildfire smoke exposure during pregnancy and risk of preterm birth in California. Environmental Research, 203, 111872.

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