The earliest weeks of pregnancy are a period of remarkable development. In a matter of weeks, the foundations of the brain, spinal cord, heart, and other major organs begin to take shape. That rapid development also makes this a particularly important period for understanding how environmental exposures may affect fetal health.
My research team at UC San Francisco conducted a study that examined whether exposure to wildfire-related air pollution during the first eight weeks of pregnancy was associated with structural birth defects. Focusing on pregnancies in California’s San Joaquin Valley, we found associations between wildfire-related fine particulate matter and several birth defects, including spina bifida.
Why birth defects and air pollution matter
Birth defects affect approximately 2 to 4 percent of infants in the United States and are a leading cause of infant mortality. Genetics can play an important role, but we are also working to understand how environmental factors may contribute.
One exposure of concern is fine particulate matter, or PM2.5 , which are tiny airborne particles that are a major component of wildfire smoke. Because these particles are small enough to travel deep into the lungs and enter the bloodstream, we are investigating how exposure during pregnancy could influence fetal development.
Examining exposure during a critical window
To explore this question, we analyzed data from 3,005 pregnancies in California’s San Joaquin Valley between 2000 and 2018, drawing on data from two large, long-running studies. The analysis included live births, stillbirths, and pregnancy terminations.
Rather than examining exposure across an entire pregnancy, the team focused on the first eight weeks of pregnancy. This is a critical window when many major organs and structures begin developing and when disruptions may contribute to structural birth defects.
The team estimated wildfire-related PM2.5 exposure using two different measures and grouped exposures from lower to higher levels. We then examined whether increasing exposure was associated with the odds of 14 different birth defects, while accounting for other factors that could affect risk.
What we found
The clearest pattern emerged for spina bifida, a neural tube defect affecting the spine and spinal cord. Higher wildfire-related PM2.5 exposure was associated with greater odds of spina bifida across multiple measures of exposure, with the strongest evidence at the highest exposure levels. This finding is consistent with previous research linking PM2.5 from other sources, including traffic-related air pollution, with neural tube defects.
The team also found associations between wildfire-related PM2.5 and cleft lip and coarctation of the aorta, a congenital heart defect. Because the study was observational, the findings do not establish that wildfire smoke causes these conditions. Additional research is needed to confirm the associations and better understand the biological processes that may be involved.
What these findings mean
The findings draw attention to an important question in environmental health: not only what someone is exposed to during pregnancy, but when that exposure occurs. Understanding the potential effects of environmental exposures during this critical period can help us identify risks that might otherwise be overlooked and inform strategies to better protect reproductive health.
As communities experience more days affected by wildfire smoke, this study adds to growing evidence that wildfire smoke may have implications beyond immediate health effects. For clinicians, researchers, and policymakers, it underscores the importance of reducing exposure and protecting vulnerable populations during critical stages of development.
Title: Wildland fire smoke and Birth Defects in California
Authors: Amy M Padula, Jonathan A Mayo, Fred W Lurmann, Nathan R Pavlovic, Gary M Shaw
About the author
Amy Padula, PhD, MSc, is a Professor in the Department of Obstetrics, Gynecology and Reproductive Sciences and the Acting Director for UCSF Program on Reproductive Health and the Environment. Additionally, Dr. Padula is a Research Co-Director for ECO-Health Center and a Translational Research Support Core consultant on wildfire smoke exposures and study design for the EaRTH Center.
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