Pregnant women exposed to common pollutants may give birth to babies with heart deformities, indicates a recent study conducted by researchers from Los Angeles-based University of California. During their study, the researchers collected daily air pollution measurements from 30 locations around Los Angeles and correlated them to local birth registries. They found that women living in areas with the highest levels of carbon monoxide and ozone, have three times the risk of having a child with heart malformations and valve defects than those living in the least noxious neighbourhoods.

In moderately polluted areas, the risk was double. "The dose-response relationship is just about the closest you can get to a smoking gun in this kind of study,' says Beate Ritz, an epidemiologist from the university.

Normally, two children in a thousand are born with such similar heart defects, which can be life threatening and require corrective surgery before age one. The researchers found that in the most polluted areas, the incidence jumped to six per thousand. According to the researchers the situation could be worse. "The effects are probably much greater than detected because the worst cases result in miscarriages,' Ritz says.