Air pollution has been linked to lower birthweight in babies. In a study reported in the Journal of the American Medical Association, researchers examined the proportion of low-weight babies born to mothers exposed to heavy doses of soot and ash during the World Trade Center attack of September 11, 2001. Of the 182 babies born to these mothers, 15 were classified as having low weight. Of 2300 babies born in the same time period in New York in another hospital, 92 were classified as having low weight.