Wildfire smoke and pregnancy: what the science tells us and why it matters right now

As massive wildfires send smoke billowing across the mid-Atlantic, northeastern United States, and Midwest, many people are focused on the immediate effects of breathing smoky air: burning eyes, irritated throats, and worsening asthma. But for pregnant women, the risks may run deeper and last longer than the smoke itself.

Wildfires are no longer just a problem in the western US. Smoke from fires burning hundreds or thousands of miles away can travel across state lines and blanket entire regions in harmful fine particulate matter. What happens during those smoke-filled days and weeks matters enormously, especially during pregnancy.

My colleagues and I have spent years studying how wildfire smoke affects pregnant people and their babies. What we are finding is sobering, and the current fire season makes it more urgent than ever to share what the science tells us.

Wildfire smoke and life-threatening pregnancy complications

In one of the largest studies of its kind, my colleagues and I examined birth records for more than 4.5 million births in California between 2007 and 2018. We looked at whether exposure to wildfire smoke during pregnancy was associated with potentially life-threatening complications related to pregnancy or delivery, such as blood transfusions, organ failure, and sepsis.

The results were striking. Those with high smoke exposure during pregnancy had higher risk of complications compared to those with low exposure. The second and third trimesters appeared to be periods of particular vulnerability.

Perhaps most concerning were the equity findings. The association between wildfire smoke and severe pregnancy complications was more pronounced among Asian and Pacific Islander and Black pregnant people, groups that already face disproportionate barriers to maternal health care. Wildfires are not just a climate crisis. They are a health crisis shaping racial and ethnic inequities in who survives pregnancy safely.

Recommendations

Given the pregnancy and health outcomes of wildfire smoke exposure, many of us who study this problem have provided recommendations for how people can protect themselves: 

• Keeping windows and doors closed
• Using a HEPA air filter (you can make one)
• Wearing an N95 mask when going outdoors
• Rescheduling outdoor activities or moving exercise to indoor spaces

These recommendations are especially important for pregnant women and children, particularly when the Air Quality Index (AQI) is above 50. Yet, because the East Coast and Midwest have limited experience with wildfires, information on what to do and how to protect one’s health is not well known. It is critical that people learn about how the air outside their window carries risks that extend beyond their own lungs.

About the author

Amy Padula, PhD, MSc, is the Acting Director for UCSF Program on Reproductive Health and the Environment. Additionally, Dr. Padula is a Research Co-Director for ECO-Health UC and a Translational Research Support Core consultant on wildfire smoke exposures and study design for the EaRTH Center.