Updated 16 October 2013

Air pollution tied to high blood pressure in pregnancy

Pregnant women who live in neighbourhoods with lots of air pollution may be slightly more likely to develop high blood pressure.

Pregnant women who live in neighbourhoods with lots of air pollution may be slightly more likely to develop high blood pressure, a new study says.

Past research suggests people with high blood pressure have often been exposed to more air pollution in the past than those with normal blood pressure. But few studies have looked to see whether that's the case for pregnant women.

Women develop high blood pressure during about one in ten pregnancies. Having so-called gestational hypertension makes it more likely that a woman will need a caesarean section, that she will give birth early and that her baby will be born small. "Our results suggest air pollution does have some impact on the risk of gestational hypertension," said epidemiologist Dr Xiaohui Xu.

He led the study at the University of Florida in Gainesville."This could have some subsequent effects on both maternal and foetal health," Xu told Reuters Health. However, he said, "This was a pilot study, meaning it was meant to test for any potential impact of pollution on blood pressure." Researchers said the results still leave many questions unanswered.

Xu and his colleagues used data on about 22 000 women who gave birth in Jacksonville, Florida, in 2004 and 2005. Birth records showed just over 1 000 women, close to 5%, developed high blood pressure during pregnancy.

More research needed

The researchers linked each woman's home address to data from the nearest US Environmental Protection Agency air quality monitor. Monitors record how much nitrogen dioxide, carbon monoxide and other pollutants are in the air each day.

Women who lived near monitors that recorded high levels of four pollutants, including nitrogen dioxide and fine particle pollution, throughout pregnancy had 12% to 24% higher odds of getting hypertension than women with less exposure.

The patterns were similar when the researchers looked only at exposure to air pollution during the first trimester or second trimester, they reported in the Journal of Epidemiology and Community Health. "The study is provocative without being definitive in any way," said Dr Jodi Abbott, an associate professor of maternal-foetal medicine at the Boston University School of Medicine.

Abbott, who was not involved in the research, said it had some key limitations. For example, some factors that affect a woman's risk of getting high blood pressure, such as her weight, were not taken into account. In addition, the study did not look at whether any women moved to a different neighbourhood while pregnant or spent most of their time away from home, where pollution was measured.

For those reasons, Abbott told Reuters Health, more research is needed to determine whether there are any blood pressure-related benefits to moving to an area with less pollution, or to staying indoors on high-pollution days while pregnant. "I would not make any recommendations to my patients based on this research," she said. The author is a student at the Boston University School of Medicine, and Abbott is a former professor of hers.


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