Women exposed to even low levels of urban air pollution during pregnancy may be at increased risk of having babies with low birth weights, according to recent study results from Europe.
Based on data for more than 74,000 women in 12 European countries over a 15-year period, researchers said that if pollution levels were lowered to limits set by the World Health Organization (WHO), 22 percent of cases of low birth weight could be avoided.
"This is similar to the number of cases that would be prevented by cessation of maternal smoking during pregnancy in this European population," said lead author Dr. Marie Pedersen from the Center for Research in Environmental Epidemiology in Barcelona, Spain.
Babies who weigh less than 5.5 pounds at birth are at increased risk of respiratory problems in childhood, as well as other disorders later in life.
Pedersen's team looked at 14 studies of pregnant women who had children at full term between 1994 and 2011. She told Reuters Health that the researchers focused on residential rather than industrial areas, and selected cities that are smaller and have less dense traffic than the average U.S. city.
The researchers obtained detailed birth records – which included home addresses during pregnancy, infant birth weight and gestational age – from maternal health centers in Scandinavia, Western Europe, England, Lithuania and Greece.
They also sent teams to residential areas in the study to measure pollution levels over three seasons. Pedersen and her colleagues used further data from air monitoring stations, and combined it with information on traffic density and land use.
When they looked at women's exposure during pregnancy to the type of fine particles in vehicle exhaust and some industrial air pollution, they found that for every increase of 5 micrograms per cubic meter of air, the risk of low birth weight at term rises by 18 percent.
In addition to the babies' weight at birth, the study looked at their head circumference because of its potential effect on brain development, Pedersen said. They found reductions in the head sizes of babies whose mothers were exposed to average small-particle concentrations of more than 15 micrograms per square meter.
Researchers took into account factors such as maternal smoking, age, height, weight and education, and still concluded that air pollutants – especially fine particulates – and traffic density were tied to an increased risk of low birth weight and reduced average head circumference at birth.
The results of the study were published in The Lancet Respiratory Medicine journal.
Among the women studied, the average exposure levels to fine particulates during pregnancy ranged from less than 10 micrograms per cubic meter of air to nearly 30 micrograms.
Current European Union air quality standards recommend limiting a person's average fine particulate exposure over the course of a year to no more than 25 micrograms per cubic meter.
The U.S. Environmental Protection Agency (EPA) sets an upper limit for a 24-hour period of 35 micrograms per cubic meter, but in 2013 the EPA lowered the annual exposure limit to 12 micrograms per cubic meter. The WHO standard is no more than an average of 10 micrograms per cubic meter.
If the women in the study had all been exposed to only the WHO standard for particulates, Pedersen said, 145 cases of low birth weight among 50,151 babies would have been prevented.
"In setting new more stringent standards for ambient air pollution, the United States has taken a leadership role," said Tracey Woodruff, director of the Program on Reproductive Health and the Environment at the University of California, San Francisco. But most cities in the United States are currently out of compliance, Reuters news agency said.
"While Europe has better regulations on toxic chemicals, the United States has been a leader in this area, and it could be that this study will be more evidence for the Europeans to take action," said Woodruff, who has researched the effects of pollution exposure during pregnancy.
Pedersen said pregnant women worldwide are exposed to air pollution at similar or higher concentrations than those found in her group's study, and the results "provide a clear message to policy makers to improve the quality of the air we all share."
"We need cars and we need to heat our homes, but I think it is possible to develop cleaner cities," she said. "It's a change that can happen and I really hope it will, because there are so many bad health outcomes related to air pollution."
Dr. Jonathan Grigg from Queen Mary University of London said that "acceptable levels (of air pollution) may well need to be revised downward in the light of this and other studies."
Although this would involve weighing costs and benefits, "policy makers also have to take a precautionary approach when considering children's health," said Grigg, who wrote a commentary accompanying Pedersen's study and is co-chair of the Royal College of Physicians Working Party on air quality and life effects.
Grigg, a London resident, told Reuters Health in an email that he would like to place cell-phone size personal monitors onto pregnant women to see what determines how much air pollution they are exposed to. That could suggest generic precautions, including avoiding walking next to heavily used roads, that do not "either impact on lifestyle or make women feel guilty," he said.
He also suggested that policy makers take steps to reduce urban air pollution by requiring reductions in emissions by cars, taxis and buses. Development of stop/start technology to prevent idling, and requiring fuel cell power for buses, would also help, he said.