Women living near major, heavily trafficked roads were more likely to give birth prematurely, perhaps due to traffic-related air pollution, according to a Japanese study.
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 150km west of Tokyo, obtaining detailed records on each pregnancy and how close to major roads mothers lived.
"Air pollution is considered to be a potentially important risk factor of preterm births," Yorifuji said.
Overall, 15pc of women living within 200 metres gave birth before 37 weeks, compared to 10pc 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 50pc 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.
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 foetus.