Link between wildfire smoke, preterm birth driven by spontaneous preterm birth

Increases in spontaneous preterm birth drove the association between wildfire smoke exposure and increased risk for preterm birth, according to data presented at The Pregnancy Meeting.

“As fire seasons continue to worsen in California, I have had numerous patients ask me if they should be worried about their exposure to poor air quality during their pregnancy,” Anne R. Waldrop, MD, a maternal-fetal medicine fellow at Stanford University in Palo Alto, California, told Healio. “I realized little is known regarding the risks of these abrupt changes in air quality with vulnerable populations, like pregnant persons, and research was needed to guide our counseling.

“More specifically, this study developed from the emerging understanding of an association with preterm birth and wildfire smoke exposure and the work from Sam Heft-Neal, PhD, and colleagues,” Waldrop said. “After this work and findings of an association of preterm birth with wildfire smoke exposure, we wanted to take a deeper dive to better understand the potential drivers of this association.

Waldrop and colleagues identified birth certificates available from hospital deliveries in California from 2007 to 2012. For each pregnancy, the researchers estimated ZIP code-level wildfire smoke based on satellite-detected smoke plume boundaries and surface particulate matter (PM_2.5) concentrations. Estimates were used to determine the number of days of smoke exposure between 4 weeks before conception and 20 weeks’ gestation.

The primary outcomes were preterm birth phenotypes and hypertensive disorders of pregnancy, which is a major factor in medically indicated preterm birth, according to the researchers.

Among 2,548,347 pregnant people included in the study, 86% had at least 1 day of wildfire smoke exposure. On average, there were 7.5 days of exposure from 4 weeks before conception to 20 weeks’ gestation.

There were no associations between wildfire smoke exposure and hypertensive disorders of pregnancy or medically indicated preterm birth. Smoke exposure was associated with a greater risk for spontaneous preterm birth (P < .0001), with each additional day of exposure increasing the odds of spontaneous preterm birth by 0.3%.

“Clinically, this work validates the association of preterm birth and wildfire smoke exposure and gives us a better understanding on the type of preterm birth risk,” Waldrop said. “It additionally validates the unique risks pregnant persons face in the setting of abrupt changes in air quality, highlighting the need for mitigation strategies for this vulnerable population.”

Future researchers should work to better understand the effects wildfire smoke exposure has on pregnant people and their newborns, Waldrop said.

References:

• Heft-Neal S, et al. Environ Res. 2022;doi:10.1016/j.envres.2021.111872.
• Waldrop AR, et al. Antenatal wildfire smoke exposure and hypertensive disorders of pregnancy. Presented at: The Pregnancy Meeting; Feb. 6-11, 2023; San Francisco.