Pollution caused by car exhausts and heavy industry could be more harmful to pregnant women than smoking, a new study has found.
Research conducted by the University of Florida suggests that two specific pollutants: carbon monoxide and sulphur dioxide, are linked to high blood pressure disorders during pregnancy.
Carbon monoxide is a chief constituent of car exhaust gases.
Speaking to the Daily Mail, Dr Xiaohui Xu, an assistant professor of epidemiology in the colleges of Public Health and Health Professions and Medicine, said: "Foetal development is very sensitive to environmental factors.
"That is why we wanted to do this research. Hypertension (high blood pressure), in particular, is associated with increased morbidity and mortality, causing a lot of problems for the mother and foetus, including pre-term delivery."
Hypertension is estimated to affect around 10 per cent of pregnancies, though little is known about what can cause it to develop in pregnant women.
The study, which sampled 22,000 pregnant women in the Jacksonville area, concluded that exposure to air pollutants in the first two trimesters of pregnancy increased the risk of a hypertensive disorder, after controlling exposure to other factors, such as a person's socioeconomic status and whether they were a smoker.
They now plan to expand the study to pinpoint other harmful factors.
"We are trying to look at several outcomes," Dr Xu said.
"We also want to look at preterm delivery and low birth-weight and find out what the effects of breathing contaminated air are on foetal development."