"Fire season has become a hard-to-breathe reality in much of the western United States. But the blazes may affect more than air quality or even human lungs. A recent study attributes as many as 7,000 preterm births in California to wildfire smoke exposure.
Researchers from Stanford University analyzed data on 3 million births in the Golden State between 2007 and 2012, matching it to data on wildfire smoke plumes in the period to determine the number of “smoke days” experienced during the pregnancies.
The analysis revealed associations between smoke exposure and preterm birth, even when the data was adjusted to exclude other factors that can lead to premature babies, such as race and income. Every day of wildfire exposure upped the risk by half a percentage point on average, and each week — the average each expectant mother was exposed to during the period — worked out to a 3.4 percent increase in preterm births."