Women exposed to high ozone pollutant levels during pregnancy have a higher risk of their babies being significantly underweight, according to researchers at the Keck School of Medicine of the University of Southern California. The study, appearing in the journal Environmental Health Perspectives, found that air heavily polluted with ozone can cause intra-uterine growth retardation.
Study author Frank D. Gilliland and co-researchers examined birth records from nearly 4,000 children who were born in California between 1975 and 1987 as well as levels of major pollutants in a dozen Southern California communities.
The researchers found that each increase of 12 parts per billion (ppb) of average daily ozone levels over a mother's entire pregnancy was associated with a drop of 47.2 grams (about a tenth of a pound) in a baby's birth weight. Gilliland said the association was even stronger for ozone exposure over the second and third trimesters. He added that for each 17 ppb increase in average daily ozone levels during a mother's third trimester of pregnancy, the risk of intra-uterine growth retardation increased by 20 percent. The study indicates that the effects were strongest when total average daily ozone exposure rose above 30 ppb. Ozone levels varied from less than 20 ppb in cleaner areas to above 40 ppb in more polluted areas of Southern California.
They also found that carbon monoxide pollutant levels affected birth weight. Each increase of 1.4 parts per million of carbon monoxide concentration during the first trimester was associated with a 21.7 g (about one-twentieth of a pound) decrease in birth weight and a 20 percent increase in risk of intra-uterine growth retardation.
Gilliland said the ozone findings echoed results from animal studies. Pregnant rats were found to be particularly vulnerable to lung inflammation from ozone. Researchers suspect that inflammation from ozone may prompt the release of certain chemicals into the bloodstream, which may harm the placenta.
"These findings add further evidence that our ozone standards are not protecting the most vulnerable members of the population," concluded Gilliland.
Source: University of Southern California
