A new study by scientists in California concluded that exposure to local traffic-generated air pollution is linked to an increased risk of preeclampsia and preterm births in Southern Californian women.
The study was the work of Dr Jun Wu, assistant professor in the College of Health Sciences and the Epidemiology School of Medicine at the University of California, Irvine, and colleagues, and is published as an early online issue of the journal Environmental Health Perspectives.
Preeclampsia is a major complication of pregnancy and a leading cause of preterm birth and maternal and infant illness and death.
The condition usually occurs in the late 2nd or 3rd trimester, although it can happen earlier. The condition affects both mother and fetus and arises in 5 to 8 per cent of pregnancies. It progresses rapidly and is characterized by high blood pressure and protein in the urine.
Although preeclampsia is usually accompanied by sudden gain in weight, headaches and vision disturbance, some women get few symptoms, even when the condition advances rapidly.
Wu and colleagues wrote that while there is evidence linking air pollution to adverse pregnancy outcomes, few studies have looked at how local traffic-generated emissions might be linked to preeclampsia as well as preterm births.
For the study they identified over 80,000 records of single births from four hospitals in Los Angeles and Orange Counties in California, spanning 1997 to 2006.
Using a dispersion model called CALINE4 they estimated the individual exposure to local traffic-generated oxides of nitrogen (NOx) and fine particles (PM2.5 particles) across the entire pregnancy.
Then Wu and colleagues used a statistical tool called logistic regression to estimate how strong any links might be between air pollution exposure and preeclampsia and preterm delivery (including moderate and very preterm).
The results showed:
- Maternal exposure to local traffic-generated NOx and PM2.5 was linked to higher risk of preeclampsia and preterm birth.
- The highest levels of NOx and PM2.5 exposure (the top 25 per cent or quartiles) increased the risk of preeclampsia by 33 per cent and 42 per cent respectively.
- The risk of very preterm delivery (under 30 weeks gestation) increased by 128 per cent and 81 per cent for women with the highest levels (top quartiles) of NOx and PM2.5 exposure respectively.
The authors concluded that:
“Exposure to local traffic-generated air pollution during pregnancy increases the risk of preeclampsia and preterm birth in Southern Californian women. “
“These results provide further evidence that air pollution is associated with adverse reproductive outcomes,” they added.
Fine particles contain acids (such as nitrates and sulfates), organic chemicals, metals, dust, soil, and allergens (bits of pollen and mold spores) and mostly come directly or indirectly from power plants, factories and automobiles.
PM2.5 particles are up to 2.5 micrometers in diameter and are thought to be the most poisonous type. According to the US Environmental Protection Agency (EPA), health studies have linked exposure to this grade of particles to premature death from heart or lung disease and aggravation of a number of conditions resulting in increased cardiovascular symptoms.
In 1997 the EPA set the annual standard as a level of “15 micrograms per cubic meter, based on the 3-year average of annual mean PM2.5 concentrations” so that the general public can see “whether the air quality in a given area is healthy”.
This week the EPA released tthe National Air Toxics Assessment (NATA), which based on 2002 air emissions data, shows that Los Angeles has nearly double the national average risk of cancer due “air toxics”, with the heart of the city having the highest level in in the country.
The 2002 NATA estimates that most people in the US have an average cancer risk of 36 in 1 million (if exposed to 2002 emission levels over the course of a lifetime). But about 2 million people have an increased cancer risk of more than 100 in 1 million.
And for residents of Cerritos in the centre of Los Angeles, the cancer risk due to air toxics was estimated at 1,200 in 1 million, the highest in the whole of the US and more than 33 times the national average.
For most of the rest of Los Angeles the risk was estimated to be between 50 and 75 per million, up to double the national average.
“Association between Local Traffic-Generated Air Pollution and Preeclampsia and Preterm Delivery in the South Coast Air Basin of California.”
Jun Wu, Cizao Ren, Ralph J. Delfino, Judith Chung, Michelle Wilhelm, Beate Ritz
Environmental Health Perspectives Online 24 June 2009.
doi: 10.1289/ehp.0800334
Additional sources: Preeclampsia Foundation, EPA.
Written by: Catharine Paddock, PhD