A recent study in The Lancet Planetary Health assessed air pollution exposure in more than 750 pregnant women in Barcelona, Spain, using neurosonography imaging to examine their baby’s fetal brain structure during the third trimester. Researchers measured the mothers’ exposure to nitrogen dioxide, fine particles and black carbon at home, work and during daily travel. Black carbon forms when fossil fuels, wood or biologic materials burn incompletely.

The study revealed that higher exposure to these pollutants was linked to changes in the shape and size of certain brain structures. Fetuses exposed to higher levels of black carbon had larger fluid-filled spaces in the brain, a larger cerebellum and a shallower fold in the brain known as the Sylvian fissure. These changes suggest slower or altered brain development. The study also found that fetal brains may be most sensitive to the effects of pollution during the second and third trimesters of pregnancy.