Pregnant moms who live in grimy, polluted New York City and also experience economic hardship, give birth to children who have lower IQs that will follow them throughout life, according to a study from Columbia University.

Researchers at the Columbia Center for Children’s Environmental Health at the Mailman School of Public Health found that children born to moms exposed to high levels of pollutants called PAHs (polycyclic aromatic hydrocarbons) during pregnancy and reported economic hardship, scored significantly lower on IQ tests at age 7 than children born to mothers with less exposure to pollutants and greater economic security.

PAHs are one of the most widespread pollutants in the environment, mainly as a result of burning fossil fuels, such as gasoline, diesel, and heating oil.

Previous research at Columbia had shown that prenatal exposure to PAHs was linked to developmental delay at the age of 3, reduced IQ at age 5, and symptoms of anxiety and depression at age 7. But researchers didn't know if the effects were long-lasting.

Researchers tracked 276 minority mother-child pairs from poor areas of New York City. At birth, the blood from each baby's umbilical cord was examined for levels of PAHs. Mothers also reported economic hardships, such as difficulty feeding and clothing their children at frequent points through the child's early years.

At the age of 7, researchers used the Wechsler Intelligence Scale for Children to measure IQ. They found that the children of mothers who were exposed to high levels of PAH during pregnancy and reported greater material hardship, scored lower on tests of reasoning, working memory, and overall IQ when compared to children who were exposed to lower levels of PAHs.

The children's overall IQ scores were 6.6 points lower, and they scored 8 points lower on working memory, which is the part of cognitive function that allows us to think and take action, and is crucial for learning to read and understand math. The average score on an IQ test is 100.

"The findings support policy interventions to reduce air pollution exposure in urban areas as well as programs to screen women early in pregnancy to identify those in need of psychological or material support," says lead author Dr. Rederica Perera.

The study was published in the journal Neurotoxicity and Teratology.