Air Pollution Increases Risk of Preeclampsia and Hypertension During Pregnancy, Study

Breathing polluted air increases the risk of preeclampsia and hypertension in pregnant women, University of Florida researchers find.

Air pollutants are as toxic as cigarette smoke, or more. On studying data of 22,000 pregnant women who gave birth between 2004 and 2005 and comparing it to Environmental Protection Agency estimates of air pollution during the same period, researchers found that breathing polluted air during pregnancy increases the risk of high blood pressure disorders.

"Fetal development is very sensitive to environmental factors," said Xiaohui Xu, M.D., Ph.D., an assistant professor of epidemiology in the colleges of Public Health and Health Professions and Medicine in a press statement. "That is why we wanted to do this research. Hypertension (high blood pressure), in particular, is associated with increased morbidity and mortality, causing a lot of problems for the mother and fetus, including preterm delivery."

Researchers noted that 4.7 percent of the women studied developed a hypertensive disorder during pregnancy. Most of these women were among those that were exposed to air pollutants throughout the first two trimesters.

Special mention is made of carbon monoxide and sulphur dioxide, two very common particulate matters found in polluted air. These pollutants contain acids, metals, dust and soil particles that are released from industries and forest fires. They are also created when gases released into the air react with each other. While sulphur dioxide is produced by industries and power plants, carbon monoxide is mostly produced by car exhaust.

Hypertensive disorders such as gestational hypertension, preeclampsia and the deadly condition it leads to, eclampsia, affect about 10 percent of pregnancies. Despite the serious risks to mother and baby, little is known about what specifically causes these conditions to develop in pregnant women. Researchers were not able to determine whether exposure early in the pregnancy or late in the pregnancy was more likely to increase a woman's risk for hypertension.

Authors of the study now plan on conducting further research to better understand other conditions that may be affected by air pollution.

"We are trying to look at several outcomes," Xu said. "We also want to look at preterm delivery and low birth-weight and find out what the effects of breathing contaminated air are on fetal development."

High blood pressure and hypertensive problems occur in 6 percent to 8 percent of all pregnancies in the U.S., about 70 percent of which are first-time pregnancies. According tothe National High Blood Pressure Education Program (NHBPEP), preeclampsia does not in general increase a woman's risk for developing chronic hypertension or other heart-related problems. The NHBPEP also reports that in women with normal blood pressure who develop preeclampsia after the 20th week of their first pregnancy, short-term complications--including increased blood pressure--usually go away within about 6 weeks after delivery.

There is national guidance on the care of women with severe preeclampsia or eclampsia and on screening for hypertensive disorders during pregnancy. However, there has been no guidance on the assessment and care of women and their babies after a diagnosis of hypertension (including the use of antihypertensive treatment) or on maternity care for women with chronic hypertension.

Findings of the story were published in the Journal of Epidemiology & Community Health and funded through grant K01ES019177 from the National Institute of Environmental Health Sciences.