Exposure to high levels of air pollution during pregnancy might increase the chance of the unborn child eventually developing asthma, researchers have said.

A team from the Mount Sinai School of Medicine in New York carried out a study which involved 376 mothers and their babies who lived in the Boston metropolitan area.

The researchers wanted to look at how air pollution might impact the pregnancy and the child once it is eventually born.

In the UK, it is believed that one in 12 people have asthma which causes the airways to narrow and swell, sometimes making it harder to breathe.

During the trial each participating woman had their daily exposure to ultra-fine particles  associated with pollution measured.

The research team found evidence of more particles among the females who lived near busy roads which had higher volumes of traffic.

Three years later the same women were visited so the researchers could find out which of the children born to the women involved in the study had developed asthma.

In total, 18 per cent of the children born to mothers who were exposed to high levels of ultra-fine particle air pollution developed asthma. The findings also suggested that female babies were more prone to develop the breathing condition when compared to the boys.

The research team say this is the first time exposure to air pollution during pregnancy has been linked to asthma post birth.

Speaking to the MailOnline, lead researcher Dr Rosalind Wright, said: “This research is an important early step in building the evidence base that can lead to better monitoring of exposure to ultra fine particles in the United States and ultimately to regulation.

“As we advance methods for measuring these tiny particles, we hope for replication of these findings, both within different geographic areas across the United States as well as globally.

“Childhood asthma remains a global epidemic that is likely to grow with the anticipated rise in particulate air pollution exposures due to effects of climate change.”

Air pollution in pregnancy increases asthma risk in unborn child