Dirty air has been linked to slightly lowered birth weights among babies born in New York City, according to a new study.

David Savitz, an investigator from the Alpert Medical School of Brown University, told Reuters Health the study adds to others showing the adverse health effects of polluted air. "We had an opportunity to use a unique data resource in New York City that was designed to estimate exposure throughout the city, which allowed us to improve on past studies, as well as examine a large, ethnically diverse population," he said.

Savitz and his colleagues pulled the birth weights of more than 250,000 babies born in the city from 2008 to 2010, using information from the New York City Community Air Survey to compare the two. In particular, the investigators searched for particulate matter less than 2.5 micrometers in diameter, in addition to nitrogen dioxide.

In the study group, birth weights dropped by 48 grams for every 10 microgram per cubic meter increase in the particulate matter women breathed during their pregnancies. For each 10 parts per billion increase in nitrogen dioxide, birth weight fell by 18 grams. For comparison, the U.S. Environmental Protection Agency sets a national standard of 15 micrograms of those smaller particulates over the course of the year, in addition to a limit of 53 parts per billion of nitrogen dioxide.

With regard to the drop in birth weights in New York City, Savitz called for policy change. "While these are not important for any individual, on a population level, if a large number of births are shifted by that amount, there would be a real public health concern," he said. "The message really concerns policy, raising awareness that even though we have reduced air pollution levels substantially, there is still reason to believe that further reductions would be beneficial and quite possibly, have a small beneficial effect on the health of newborns.”

A similar study this year encompassing a dozen European countries likewise found lower birth weights. “Exposure to ambient air pollutants and traffic during pregnancy is associated with restricted fetal growth,” the European investigators wrote in The Lancet. “A substantial proportion of cases of low birthweight at term could be prevented in Europe if urban air pollution was reduced.”

Source: Savitz DA, Bobb JF, Carr JL et al. Ambient Fine Particulate Matter, Nitrogen Dioxide, And Term Birth Weight In New York, New York. American Journal Of Epidemiology. 2013.