The scientists studied 806 women who had a pregnancy affected by a birth defect between 1997 and 2006, and 849 women who had healthy babies during the same period. The study examined two types of neural tube defects (spina bifida, a spinal-column malformation, and anencephaly, an underdeveloped or absent brain); cleft lip, with or without cleft palate; cleft palate only; and gastroschisis, in which the infant is born with some of his or her intestines outside the body.

"Birth defects affect one in every 33 babies, and about two-thirds of these defects are due to unknown causes. When these babies are born, they bring into a family's life an amazing number of questions, many of which we can't answer," said the paper's senior author, Gary Shaw, a professor of neonatal and developmental medicine.

Scientists studying air quality and birth-defect data for women living in California's San Joaquin Valley found that exposure to specific traffic-related air pollutants was associated with a nearly doubled risk for neural tube defects, which are malformations of the brain and spine, said the study's lead author, Amy Padula, a postdoctoral scholar in pediatrics. San Joaquin Valley is one of the smoggiest regions of the country.

Breathing traffic pollution in early pregnancy is linked to a higher risk for certain serious birth defects, according to new research from the Stanford University School of Medicine.

Nitrogen oxide and nitrogen dioxide exposures were also linked to increased risk for these defects; women with the highest nitrogen oxide exposure had nearly three times the risk of having a pregnancy affected by anencephaly than those with the lowest exposure.

After controlling for factors such as race/ethnicity, maternal education and multivitamin use, the study foiund twomen who breathed the highest levels of carbon monoxide were nearly twice as likely to have a baby with spina bifida or anencephaly as those with the lowest carbon monoxide exposure, the study found.

The researchers asked each woman for her home address during this period and scored the women's exposure to air pollutants using data from the Environmental Protection Agency as part of federally mandated air-quality monitoring. The pollutants assessed included carbon monoxide, nitrogen oxide, nitrogen dioxide, particulate matter and ozone, as well as local traffic density.

All women studied resided in the San Joaquin Valley during the first eight weeks of their pregnancies, a window of time when many birth defects develop, scientists said.

Suzan Carmichael, associate professor of neonatal and developmental medicine, was another Stanford co-author. Scientists at the University of California-Berkeley and at Sonoma Technology Inc. in Sonoma, Calif., were also involved in the work.

Further studies are needed to confirm the results of the new research and to examine other pollutants, as well as other types of birth defects, the researchers said.

The quality of earlier research linking air pollution and birth defects has been hampered by the difficulty of getting reliable data on women's exposure to pollutants, according to the Stanford scientists. The new study is the first to assess women's pollutant exposures in early pregnancy, when birth defects are developing, rather than at birth.

The study was funded by grants from the National Institute for Environmental Health Science, the U.S. Environmental Protection Agency and the Centers for Disease Control and Prevention. Stanford's Department of Pediatrics also supported the work.

Air pollutants linked to higher risk of birth defects

Stanford study associates traffic-related pollution and exposure during early pregnancy