News Release

One of the largest studies of its kind finds being exposed to wildfire smoke increases risk of going into labor prematurely

Reports and Proceedings

Society for Maternal-Fetal Medicine

Media Contacts: Karen Addis, APR,; 301-787-2394; Kerri Wade, MPA,, 202-236-1780

San Francisco, Calif. -- The detrimental effects of poor air quality on a person’s health are well documented. In pregnant people, research has shown that poor air quality, such as smog, can lead to a number of adverse outcomes, including preterm birth (PTB), one of the leading causes of infant mortality in the United States as well as globally. PTB is defined as delivery before the 37th week of pregnancy.

Now, in a new study to be presented today at the Society for Maternal-Fetal Medicine’s (SMFM) annual meeting, The Pregnancy Meeting™ — and published in the American Journal of Obstetrics & Gynecology — researchers will unveil findings that suggest that being exposed to another type of and potentially more dangerous pollutant ― smoke from wildfires ― increases a pregnant person’s chance of going into labor prematurely, also referred to as spontaneous preterm birth (versus one that is medically induced).

Wildfire smoke is especially harmful to people’s health because it contains extremely fine particles that can enter deep into the lungs and may worsen medical conditions such as asthma and heart disease. These tiny particles can also travel hundreds and sometimes thousands of miles from the wildfire’s point of origin.

Researchers reviewed birth certificates and hospital delivery data from 2007-2012 of more than 2.5 million pregnant people in California. They compared that information with daily estimates of wildfire smoke intensity — based on satellite images — by zip code.

Data revealed that four weeks prior to conception through the first 20 weeks of pregnancy, 86 percent of pregnant individuals were exposed to at least one day of wildfire smoke, with an average exposure of 7.5 days. Results showed that wildfire smoke was significantly associated with spontaneous preterm birth, and each additional day a pregnant person was exposed to wildfire smoke slightly increased the odds of delivering an infant prematurely.

“Wildfires lead to acute and abrupt changes in air quality,” says the study’s lead author Anne Waldrop, MD, a maternal-fetal medicine subspecialist fellow at Stanford University in Palo Alto, Calif. “And some emerging evidence suggests that wildfire smoke could be worse for your health than other types of pollutants. So, even as we work to decrease other forms of air pollution, with wildfires becoming more frequent, more intense, and happening on a much larger scale, exposure to wildfire smoke is a serious public health problem, especially for vulnerable populations like pregnant people.”

To view the presentation of this abstract or other Pregnancy Meeting™ abstracts and events, visit the SMFM website or contact Karen Addis at or 301-787-2394.


About the Society for Maternal-Fetal Medicine

The Society for Maternal-Fetal Medicine (SMFM), founded in 1977, is the medical professional society for maternal-fetal medicine subspecialists, who are obstetricians with additional training in high-risk pregnancies. SMFM represents more than 5,500 members who care for high-risk pregnant people and provides education, promotes research, and engages in advocacy to advance optimal and equitable perinatal outcomes for all people who desire and experience pregnancy. For more information, visit and connect with the organization on Facebook and Twitter. For the latest 2023 Annual Meeting news and updates, follow the hashtag #smfm23.


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