While pregnant, traffic pollution near home raises risk for preeclampsia

Posted: 9/4/2012

From Environmental Health News:

Exposure to traffic-related air pollution can greatly raise a pregnant woman's risk for preeclampsia, a large study from Australia has found. Preeclampsia can cause serious health problems for mother and baby. The strongest effects were observed among women exposed during the third trimester and for those who had gestational diabetes. One of a handful of studies to examine the link between air pollution and preeclampsia, it is unique because the scientists measured the women's exposures to local air pollutants generated by road traffic, including cars and diesel trucks.

What did they do?

Researchers looked at the association between preeclampsia in pregnant women and exposure to traffic-related air pollution, as measured by the estimated levels of nitrogen dioxide near the women's homes.

They examined medical records of 23,452 pregnancies in Perth, Western Australia, between January 2000 and December 2006. The mothers' residential addresses and preeclampsia diagnoses were available from government databases. The study included women who were at least 30 weeks pregnant with a singleton pregnancy.

The researchers collected air pollution, weather and traffic volume data from routine local monitoring stations throughout the region. They added the data to a statistical modeling program to estimate average nitrogen dioxide levels at each woman's home for every week of pregnancy. Nitrogen dioxide is one of the main components of traffic-related air pollution. Its levels indicate the severity of the air pollution.

The researchers looked at average nitrogen dioxide levels during the entire course of pregnancy as well as the average levels during each trimester. They adjusted for several factors, including diabetes, previous pregnancies, socioeconomic status, age, smoking and ethnicity.

What did they find?

Higher levels of traffic-related air pollution near the women's homes over the entire pregnancy resulted in a 12 percent greater risk of the women developing preeclampsia.

They looked at air pollution levels by trimester. During the third trimester, exposure to higher air pollution levels was associated with a 30 percent greater risk of developing preeclampsia.

The largest association was observed for women who already had or developed diabetes during pregnancy, although diabetes itself is a risk factor for preeclampsia.

In this subset of 1,049 women with existing or gestational diabetes during the third trimester exposure to higher levels of air pollution was associated with a 326 percent increase in the risk of preeclampsia. Over the entire pregnancy, there was a 53 percent increase in risk. Of these diabetic women, 67 developed preeclampsia.

What does it mean?

Pregnant women with the highest exposures to traffic related air pollution during their whole pregnancy had an increased risk for preeclampsia.

This is the first published study that used field measurements of traffic related air pollution to examine the association between air pollution and preeclampsia.

While scientists don't fully understand how preeclampsia develops, the basis for the condition could begin early in pregnancy.

One of the most interesting aspects of this study is that the link between air pollution and preeclampsia appears to be greatest during the third trimester - although the third trimester is also when most preeclampsia cases develop and are diagnosed. One explanation for this increased importance of third trimester exposure may be that among pregnant women who are predisposed to develop preeclampsia - such as women with diabetes - the exposure to the elevated levels of traffic-related air pollution may trigger overt disease.

Air pollution can be a challenging environmental exposure to study. While data on ambient air pollution are readily available because many governmental agencies monitor air quality, it is difficult to know exactly how much of the pollution any one person breathes. For instance, this study uses an estimate of the level of nitrogen dioxide due to traffic present at the woman's address as listed on her medical record. If the woman moved during her pregnancy, if she spends the majority of her time elsewhere or if she is rarely outside, then the exposure level assigned to her based on the stated address may be incorrect.

Even with this limitation, however, this study suggests that air pollution may contribute to another adverse health outcome.

Original here.