Exposure to wildfire smoke and heat stress both before and during pregnancy may be associated with adverse outcomes at birth, a new study has found.
Such links were particularly pronounced when exposure occurred during the month before conception and during the first trimester of pregnancy, researchers reported in the study, published in Environmental Science & Technology.
“We already know that poor air quality is associated with adverse health outcomes and that pregnant women and fetuses are especially vulnerable,” lead author Roxana Khalili, a postdoctoral researcher at the University of Southern California, said in a statement.
But Khalili and her colleagues were interested in understanding more, as the knowledge surrounding the specific of impacts of wildfire smoke during and prior to pregnancy is still limited, she explained.
Among the adverse birth outcomes that the researchers observed were small-for-gestational-age babies: infants whose birth weights are below the 10th percentile of their expected weight based on gestational age.
Lower birth weights place babies at a greater risk of health problems, from immediate issues like low oxygen levels to long-term difficulties that range from metabolic to cognitive to neurodevelopment impairments, per the study.
Meanwhile, the researchers also found that residence in a climate-vulnerable neighborhood could increase the odds of a small-for-gestational-age birth, especially among women exposed to heat stress prior to conception.
“Where you live makes a difference in your health,” Khalili said. “So does the timing of your exposure during or immediately before pregnancy.”
To draw these conclusions, Khalili and her colleagues examined 713 births between 2016 and 2020, acquired from an ongoing database of pregnant women in Los Angeles, called the Maternal and Development Risks from Environment and Social Stressors (MADRES) cohort.
They then used data from CalFIRE to identify the location, size and duration of each wildfire in Southern California during that same period.
In addition, the researchers accessed the National Oceanic and Atmospheric Administration’s hazard mapping system to assess smoke density associated with each fire. By applying sophisticated models to those calculations, they were able to estimate particle pollution exposure endured by MADRES participants.
To measure heat stress — important due to pregnancy’s impacts on body temperature regulation — Khalili and her colleagues relied on meteorological data that documented daily temperature, relative humidity and wind speed.
The researchers also identified Los Angeles neighborhoods that were most vulnerable to climate risks via both state and federal indexes — enabling them to better assess the cumulative factors of heat, smoke and socioeconomic conditions.
Going forward, Khalili expressed hope that the findings would help residents and policymakers cope with longer-lasting fire seasons.
“Understanding what’s happening to women during wildfires and excessively hot days could help us identify protective measures, develop guidance, and plan interventions,” said Khalili.
But she and her colleagues also stressed that future action would need to extend beyond simply measures that individuals can take, such as staying indoors and running air conditions.
They therefore emphasized a need for a holistic approach that could increase the adoption capacity of relevant communities and thus strengthen their resilience in a changing climate.
“As the recent Los Angeles fires have demonstrated, infrastructure, socioeconomic, and health vulnerabilities can combine with excessive climate and environmental factors to magnify health risks,” senior author Rima Habre, director of USC’s CLIMA Center, said in a statement.
“It is only by looking at the cumulative impacts of burdens communities are facing, now and into the future, that we can start to truly quantify health risks of climate hazards and target interventions to strengthen community resilience,” Habre added.