Air pollution from traffic increases risk of hypertension among pregnant women, finds study
Air pollution from traffic increases a pregnant woman's risk for dangerous increases in blood pressure, known as hypertension.
What's more, when women are exposed to particulate matter or PM2.5 during their entire pregnancy, the likelihood of developing preeclampsia — which refers to high blood pressure with protein in urine or impaired liver or kidney function — increases by about 50%, says a report by researchers from the National Toxicology Program (NTP), US Department of Health and Human Services.
According to experts, if preeclampsia worsens and causes seizures, it becomes eclampsia — a serious condition for mother and child with the potential to be fatal.
"The National Toxicology Program serves as an environmental health resource for the scientific and medical communities, health research and regulatory agencies, and public," Dr. Brandy Beverly, a health scientist with the Office of Health Assessment and Translation (OHAT) in the NTP, tells MEA WorldWide (MEAWW).
"NTP's evaluation found that exposure to traffic-related air pollution during pregnancy increases the likelihood of developing a hypertensive disorder during pregnancy, which can have significant impacts on both maternal and fetal health," Dr. Beverly adds.
Hypertensive disorders of pregnancy complicate more than 10% of pregnancies worldwide and are a leading cause of maternal and fetal illness and death.
According to the American College of Obstetrics and Gynecology, mothers with hypertension during pregnancy are more likely to have a preterm delivery. Their infants are at greater risk for low birth weight and a range of long-term health problems associated with premature birth.
"Children born to mothers who experience a hypertensive disorder during pregnancy are at a higher risk for having low birth weight, being small for their gestational age, being born prematurely, and having a range of diseases that are associated with premature delivery, all of which can have long-term impacts on their health," informs Dr. Beverly, lead scientist and researcher at the National Institute of Environmental Health Sciences, part of the National Institutes of Health.
The findings, she says, suggest that pregnant women should limit their outdoor exposure when the air quality is poor, especially if they live in urban environments.
The study says that traffic-related air pollution or TRAP contributes significantly to ambient air pollution, especially in urban settings. Air pollution has been established as a risk factor for hypertension and cardiovascular disease in adults, but this effect is less studied in other susceptible populations, say researchers.
Accordingly, scientists from NTP evaluated published research on the link between traffic-related air pollution and hypertensive disorders broken down by pollutant measurements of TRAP, such as particulate matter (PM2.5).
Other components of TRAP that NTP evaluated included nitrogen oxides, carbon monoxide, black carbon, and elemental carbon, along with parameters like traffic density and mothers' proximity to main roads.
The experts say that TRAP comes from the combustion of fossil fuels by motor vehicles. These vehicle emissions are mixtures of gases and particles that are easily inhaled and have adverse health effects. TRAP is known to be a major risk factor for cardiovascular disease, including hypertension.
"TRAP refers to air pollution exposures derived from primary emissions from motor vehicles due to fossil fuel combustion. Sources of TRAP include passenger cars, diesel trucks and buses, and nonroad equipment (for example, recreational vehicles, lawn and garden equipment)," points out the study.
"Motor vehicles emit large amounts of carbon dioxide, carbon monoxide, nitrogen and sulfur oxides, volatile organic compounds, and particulate matter. Many of these pollutants are regulated by the US Environmental Protection Agency (EPA) and are used as pollutant surrogates for TRAP," adds the study.
Based on their review, the team found that exposure to PM2.5 from traffic emissions was associated with the development of hypertensive disorders in pregnant women.
"Exposure to TRAP during pregnancy increases the likelihood of developing hypertensive disorders of pregnancy. The human bodies of evidence for traffic-related PM2.5 and nitrogen dioxide present a consistent pattern of findings that exposure to these pollutants is associated with the development of hypertensive disorders of pregnancy," the findings state.
Dr. Beverly explains that hypertensive disorders of pregnancy refer to a range of clinical conditions, all of which include high blood pressure during pregnancy. The disorders are classified into four distinct types, based on differences in the timing and onset of the symptoms.
A standard four-tier scale to classify human hazards was used in the analysis. The scale ranges from the highest hazard rating of "known", followed by "presumed", then "suspected", and finally, "not classifiable".
The team looked at the combined evidence and concluded that traffic-related air pollution is a "presumed human hazard for hypertensive disorders during pregnancy".
"Hypertensive disorders of pregnancy represent a spectrum of disorders that range in severity. The studies included in this evaluation most frequently evaluated preeclampsia, and when studies were available, associations between traffic-related air pollution and preeclampsia were discussed," Dr. Beverly shares.
"However, the NTP hazard conclusion was based on the evidence for associations between traffic-related air pollution and health outcomes across the spectrum of hypertensive disorders of pregnancy without differentiation," she continues.
"Or, in other words, we concluded that TRAP is a presumed human hazard for hypertensive disorders during pregnancy, though we weren’t able to distinguish between the four types of disorders," she tells MEAWW.
The evaluation underwent external peer review involving experts from academia and industry, who evaluated NTP's draft conclusions and agreed unanimously with NTP's conclusion.