Air pollution increases 10 percent chances of underweight babies, said a study Wednesday in the journal Environmental Health Perspectives.  Mothers who breathe polluted air are significantly likely to give birth to underweight babies than mothers living in areas with good air."As air pollution increases we can see that more babies are smaller at birth, which in turn puts them at risk of poor health later in life," said Tanja Pless-Mulloli, professor of Newcastle University.The researchers said sources of air pollution include among others traffic exhaust, power plants, and even dust. It is unknown yet why maternal exposure to air pollution could impact fetal growth.However, one theory is that air pollution impacts the connection between the placenta and the uterus, which could reduce the transfer of nutrients to the fetus.Another is that air pollution may stress the mother's body, which could affect fetal growth.Xinhuanet