Researchers in Boston found a link between fetal exposure to ultrafine air pollution and future asthma development among toddlers. The study followed 376 women throughout their pregnancy and stayed in touch every four months until their children reached an average age of 3-4. Around 18% of women in the study, a little over one in five, had a child who developed asthma. The authors found girls were more likely to develop asthma if they were exposed to tiny pollution particles later in the pregnancy, such as the third trimester. The timing stayed constant for boys.

To measure exposure to ultrafine air pollution, the researchers set up stations and satellites to evaluate emissions of pollution particles, which can come from gasoline emitted from cars and airplanes – and is more common in cities. They adjusted their analysis for a variety of factors, including maternal age, education, race, obesity, previous exposure to smoke, and the child’s exposure to ultrafine air pollution during infancy. They conclude future research in other regions, and studies that explore underlying mechanisms, will help scientists confirm and explain these connections. Future research, they note, may also help shape public health policies.

The study published in the American Journal of Respiratory & Critical Care Medicine and was supported by the National Institute of Environmental Health Sciences, the National Institute on Minority Health and Health Disparities, and the National Heart, Lung, and Blood Institute.