As the 2020 wildfire season kicked into high gear, smoke blanketed the West Coast from Los Angeles to Seattle, and pregnant women throughout the region began to wonder—should I be worried about the effects of the smoke on my health and that of my baby?
The health effects of smoke inhalation are primarily driven by respiratory exposure to small particulate matter less than 2.5 μm across (PM2.5). Increased exposure to PM2.5 has been associated with increased risk of hypertensive disorders of pregnancy, fetal growth restriction, abnormal placentation and prematurity.1 PM2.5 generated by wildfire is more toxic than typical ambient PM2.5. It has been associated with an increased incidence of bronchitis, asthma, and arrhythmias, resulting in increased admissions for respiratory complications and even, in some series, respiratory mortality.2 While there are no studies that specifically evaluate the impact of wildfire smoke inhalation on maternal health, pregnant women may be at increased risk of harm due to physiologic adaptations to pregnancy. Increased tidal volumes and respiratory rates increase pregnant women's exposure to environmental pollutants and PM2.5 and likely make them more susceptible to the adverse respiratory effects of wildfire smoke exposure.
More commonly studied are the effects of wildfire smoke exposure on the developing fetus. The available literature suggests that both single episode and long-term exposure can have adverse obstetric outcomes, most significantly low birthweight and preterm birth. A time-series study comparing the average birthweight of California-born infants exposed to any amount of wildfire smoke in utero to those who were unexposed found those who were exposed had slightly decreased average birthweight (3.3g to 9.7g, depending on trimester).3 These findings were later supported by a large Coloradoan cohort study that demonstrated a dose-dependent association of first trimester wildfire smoke exposure and decreased birthweight, as well as a small dose-dependent increased risk of preterm birth with smoke exposure throughout pregnancy.4 Risks of gestational diabetes and gestational hypertension were increased in women with wildfire smoke exposure in the first trimester.
Despite these studies, an enormous number of unknowns remain regarding the impact of wildfire smoke on the developing fetus. In addition to PM2.5, areas affected by wildfire smokes have increased levels of aromatic hydrocarbons, carbon monoxide and other volatile organic compounds, which, in other contexts, have been associated with fetal malformations and demise. As climate change increases the intensity and frequency of wildfires in the American West, understanding the impact of wildfire smoke on pregnant women and their children will continue to be a critical area for public health.
 Melody SM, Ford J, Wills K, Venn A, Johnston FH. Maternal exposure to short-to medium-term outdoor air pollution and obstetric and neonatal outcomes: A systematic review. Environ Pollut. 2019;244:915-925. doi:10.1016/j.envpol.2018.10.086
2 Dennekamp M, Abramson MJ. The effects of bushfire smoke on respiratory health. Respirology. 2011;16(2):198-209. doi:10.1111/j.1440-1843.2010.01868.x
3 Holstius DM, Reid CE, Jesdale BM, Morello-Frosch R. Birth weight following pregnancy during the 2003 Southern California wildfires. Environ Health Perspect. 2012;120(9):1340-1345. doi:10.1289/ehp.1104515
4 Abdo M, Ward I, O'Dell K, et al. Impact of Wildfire Smoke on Adverse Pregnancy Outcomes in Colorado, 2007-2015. Int J Environ Res Public Health. 2019;16(19):3720. Published 2019 Oct 2. doi:10.3390/ijerph16193720