From The London Daily Mail:

Expectant mothers living in large towns or cities are a third more likely to give birth prematurely because of pollution, research suggests.

Traffic fumes are the biggest culprit, with chemicals called polycyclic aromatic hydrocarbons (PAH), a by-product of petrol, producing a 30 per cent increase in risk.

Ammonium nitrate from agriculture and industry heightened the threat of premature birth by a fifth – 21 per cent – while benzene, a petrochemical, and diesel fumes caused a 10 per cent increase.

Researchers also noted the concentrations of pollutants were higher in winter than in summer, and coastal cities had cleaner air than those further inland.

Study author Dr Beate Ritz said: ‘Air pollution is known to be associated with low birth weight and premature birth.

‘Our results show traffic-related PAH are of special concern as pollutants and that PAH sources besides traffic contributed to premature birth.