Breathing the air outside the homes may be just as toxic to pregnant women - if not more so - as breathing in cigarette smoke, increasing a mom-to-be's risk of developing complications such as preeclampsia, according to the findings by University of Florida.
Researchers compared birth data with Environmental Protection Agency estimates of air pollution in US, finding that heavy exposure to four air pollutants led to a significantly increased risk for developing a high blood pressure disorder during pregnancy.
"Foetal development is very sensitive to environmental factors," said Xiaohui Xu.
Hypertensive disorders such as gestational hypertension, preeclampsia and the deadly condition it leads to, eclampsia, affect about 10 per cent of pregnancies.
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To gain a better understanding of how environmental factors may play a role in increasing the risk of developing hypertension during pregnancy, the researchers examined data from women who gave birth in Jacksonville, Florida, between 2004 and 2005 and environmental data from their communities.
The sample included more than 22,000 pregnant women.
They then gauged how much pollution the women were exposed to throughout their pregnancies using data the EPA gathered daily to measure the levels of several pollutants.
Among the sample of women, 4.7 per cent developed a hypertensive disorder during pregnancy. Exposure to air pollutants throughout the first two trimesters of pregnancy increased women's risk of developing one of these conditions, Xu said.
"It looks like the whole period has impacts for hypertension," he said.
The study was published in the Journal of Epidemiology & Community Health.