Air pollution doesn’t just cause lung cancer and asthma.

It causes premature births.

And that’s costing the United States more than $4 billion a year.

That’s the conclusion of a report released today from researchers at New York University’s Langone Medical Center.

Their findings were published in the journal Environmental Health Perspectives.

"Air pollution comes with a tremendous cost, not only in terms of human life, but also in terms of the associated economic burden to society," Dr. Leonardo Trasande, M.D., M.P.P., a professor at NYU Langone and a lead study author, said in a statement. "It is also important to note that this burden is preventable."

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Where the Numbers Come From

The researchers said air pollution is known to increase toxic chemicals in the blood and cause immune system stress.

This can weaken the placenta surrounding a fetus and cause premature birth.

For their study, Trasande and the other researchers looked at data from the Environmental Protection Agency (EPA), the Centers for Disease Control and Prevention (CDC), and the Institute of Medicine.

The team used the level of air pollution and number of premature births in different regions to come up with a formula based on exposure, Trasande told Healthline. This formula was used to estimate the number of premature births connected to air pollution in each locale.

They estimated there are 16,000 premature births in the United States every year linked to air pollution. That’s about 3 percent of all premature births, which for this study was defined as babies born after less than 37 weeks of gestation.

The concentrations were highest in Southern California, the East Coast, and the Ohio Valley.

The researchers noted the rate of premature births has declined from a peak of 12.8 percent in 2006 to 11.4 percent in 2013.

However, that number lags behind other developed nations and is too low to meet the goal of 8.1 percent by 2020 set by the March of Dimes.

Read More: Children’s Lungs Benefit from Less Air Pollution »

What it Costs

The researchers also estimated premature births cost the United States $4.3 billion every year.

They said almost $3.6 billion is lost economic productivity due to disabilities associated with premature births. Another $760 million is attributed to longer hospital stays and long-term use of medications.

To calculate the costs, the researchers used data from six previous studies and computer models that focused on early death, lowered IQ, work absences due to frequent hospitalizations, and overall poor health.

Trasande said his team plans to conduct further research into the role of specific outdoor air pollutants, especially particulate matter, to see whether any stages of pregnancy are more susceptible to the effects.

They also hope to study the issue in other countries.

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What Can Be Done

Trasande added that his team plans to share the results of the current study with policy makers in hopes of encouraging new laws and regulations to reduce air pollution.

For starters, the researchers recommended allowable emissions should be reduced for automobiles and coal-fired power plants.

Trasande told Healthline that women who are pregnant and live in areas with significant air pollution should try to minimize the time they spend outside.

He added they should also close their windows when they are inside of their homes and install air filters.

He said the research focused on air pollution as a way to reduce premature births because it is an easier cause to address.