Researchers from Emory University in the US analysed blood samples from 330 African American pregnant women in the Atlanta metropolitan area. Women living in downtown and midtown neighbourhoods, where several highways intersect, had a higher level of exposure to pollution over a year, compared to those living on the outskirts of the city, the team said. Vehicular emissions are a major contributor to PM2.5 pollution.

Two substances -- 'cortexolone' and 'lysoPE(20:3)' -- involved in the relationship between short-term exposure to air pollution and an elevated risk of early births, were identified.

Cortexolone is a glucocorticoid crucial to regulating metabolism, inflammation, and the immune response, while lysoPE(20:3) is a lipid present in cells and important for cell function.#MyCOSTrade