But Takashi Yorifuji, of the Okayama Graduate School of
Medicine, and his team said it was still too early to see a clear link, while
other medical experts said noise pollution might also be a factor.
In the study, published in "Epidemiology,"
Yorifuji and his colleagues studied more than 14,000 babies born between 1997
and 2008 in Shizuoka, about 150 km (94 miles) west of Tokyo, obtaining detailed
records on each pregnancy and how close to major roads the mothers lived.
"Air pollution is considered to be a potentially
important risk factor of preterm births," Yorifuji told Reuters Health in
an e-mail.
Overall, 15 percent of women living within 200 meters of a
major road gave birth before 37 weeks, compared to 10 percent of those living
further away. A normal pregnancy is 40 weeks.
Other factors have been tied to preterm birth as well, such
as age, job, and smoking. But even after accounting for those, the research
team found a 50 percent increase in preterm births among women living next to
highly trafficked thoroughfares.
These women also had a higher risk of delivering before 32
and 28 weeks. Very premature births carry an especially heavy public health
burden.
"In addition, we found a higher risk in housewives than
outside workers, and housewives would probably spend more time at home during
their pregnancy, and reflect more accurate exposure," Yorifuji added.
Women living close to busy roads also had about double the
risk of both high blood pressure and early rupture of the membranes surrounding
the fetus, both potential causes of prematurity.
Other exports said the findings squared with previous
studies linking air pollution to high blood pressure and inflammation, which
could lead to premature rupture of the membranes.
"Everybody always worries that it's not really living
by busy roadways, but that it's other things that makes these mothers
different," said Beate Ritz of the University of California, Los Angeles,
who reviewed Yorifuji's study for publication.
"After all the adjustments, the effect was still
there," she added, noting that noise pollution also couldn't be ruled out.
So what should a pregnant woman do if she lives under an
expressway or a block from a national highway? Yorifuji recommended that a
pregnant woman who can't avoid living near a busy highway - often unavoidable
in densely populated Japan - might want to reduce the time she is active
outside, along with cutting out smoking and improving her diet.
Others said that studies have shown that it is common for
women to move during pregnancy, and that if possible they should consider
moving away from busy roads.
