Women exposed to even low levels of urban
air pollution during pregnancy may be at heightened risk of having a low-birth
weight baby, according to a review of evidence from Europe.
Based on data for more than 74 000 women in
12 European countries over a 15-year period, researchers say that if pollution
levels were lowered to limits set by the World Health Organization (WHO), 22%
of cases of low birth weight would 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
Centre for Research in Environmental Epidemiology in Barcelona, Spain.
Babies who weigh less than 2.4 kg 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 a child at full term between 1994 and 2011.
told Reuters Health the researchers specifically focused on areas "where
people live" as opposed to industrial locations and selected cities that
are much smaller, with less dense traffic than the average American city.
The researchers were able to obtain
detailed birth records, including home addresses during pregnancy, infant birth
weight and gestational age and sex, from maternal health centres in
Scandinavia, Western Europe, England, Lithuania and Greece.
They also developed their own intensive
air-monitoring network, sending teams to residential areas in the study and
measuring pollution levels over three different seasons. Pedersen and her
colleagues also used 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%.
In addition to the babies' weight at birth,
the study looked at their head circumference because of its potential effect on
brain development, according to Pedersen. They found reductions in the head
size of babies whose mothers were exposed to average small particle
concentrations of more than 15 micrograms per square meter.
The researchers took into account factors
like maternal smoking, age, height and weight and education, and still
concluded that all air pollutants, especially fine particulates, as well as
traffic density, were tied to an increased risk of low birth weight and reduced
average head circumference at birth.
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. The results were
published in The Lancet Respiratory Medicine.
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 United States Environmental Protection
Agency (EPA) sets an upper limit for a 24-hour period of 35 micrograms per
cubic meter, but in 2013 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 Programme on
Reproductive Health and the Environment at the University of California, San
But most cities in the United States are
currently out of compliance. "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,"
added Woodruff, who has researched the effects of pollution exposure during pregnancy.
costs and benefits
Pedersen said pregnant women worldwide are
exposed to air pollution at similar or even higher concentrations than those
found in her group's study, and the results "provide a clear message to
policymakers 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, UK,
said, "'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 particulate
pollution they're exposed to.
could suggest generic precautions, like avoiding walking right next to heavily
used roads, that do not "either impact on lifestyle or make women feel
guilty," he said. He also suggested that policymakers 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.