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Pregnancy hypertension risk increased by traffic-related air pollution

Pregnant woman
Pregnant woman. (File Photo: IANS)

Findings
give new insights into the connection between poor air quality, children’s
health, and mother’s health.

Traffic-related
air pollution increases a pregnant woman’s risk for hypertension

New Delhi,
18th December 2019. A new report from the National Toxicology
Program (NTP), affiliated to U.S. Department of Health and Human Services,
suggests that traffic-related air pollution increases a pregnant woman’s risk
for dangerous increases in blood pressure, known as hypertension.

NTP
scientists evaluated published research on the link between traffic-related air
pollution, or TRAP, and hypertensive disorders broken down by pollutant
measurements of TRAP, such as particulate matter (PM2.5). PM is the term for a
mixture of solid particles and liquid droplets found in the air, and PM2.5
refers to fine inhalable particles, with diameters that are generally 2.5 micrometres
or smaller.

The
average human hair is about 70 micrometres in diameter, about 30 times larger
than the largest fine particle.

“What we
found when we reviewed the literature is that exposure to PM2.5 from traffic
emissions was associated with development of hypertensive disorders in pregnant
women,” said Brandy Beverly, Ph.D., lead scientist and researcher at the
National Institute of Environmental Health Sciences, part of the National
Institutes of Health. “When these women are exposed to PM2.5 during their
entire pregnancy, the likelihood of developing preeclampsia increases by
about 50%.”

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.

For example,
the literature suggests that women who live within a quarter of a mile of a
major roadway or in high traffic density regions may be at an increased risk
for developing hypertensive disorders of pregnancy.

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.

Hypertensive
disorders of pregnancy complicate more than 10% of pregnancies worldwide and
are a leading cause of maternal and fatal illness and death. According to the
American College of Obstetrics and Gynaecology, mothers with hypertension
during pregnancy are more likely to have a pre-term delivery. Their infants are
at greater risk for low birthweight and a range of long-term health problems
associated with pre-mature birth.

“Hypertensive
disorders of pregnancy refer to a range of clinical conditions, all of which
include high blood pressure during pregnancy,” said Beverly. “The disorders are
classified into four distinct types, based on differences in the timing and
onset of the symptoms.”

Pregnant
women may experience four types of hypertensive disorders:

Gestational
hypertension, or high blood pressure, in the second half of pregnancy.

Preeclampsia,
or high blood pressure with protein in urine or impaired liver or kidney
function, in the second half of pregnancy. If preeclampsia worsens and causes
seizures, it becomes eclampsia – a serious condition for mother and child with
the potential to be fatal.

Chronic
hypertension, or high blood pressure before pregnancy or early in pregnancy,
that continues throughout pregnancy.

Chronic
hypertension with preeclampsia, or high blood pressure before pregnancy or
early in pregnancy, that continues throughout pregnancy and is complicated by
new onset protein in the urine or impaired liver or kidney function.

Using their
standard four-tier scale to classify human hazards, NTP looked at the combined
evidence from the individual components and concluded that TRAP is a presumed
human hazard for hypertensive disorders during pregnancy, though they weren’t
able to distinguish between the four types of disorders. The scale ranges from
the highest hazard rating of “known”, followed by “presumed”, then “suspected”,
and finally, “not classifiable”.

NTP
conducted the systematic review of published research on hypertensive disorders
in pregnant women and its link to TRAP after receiving a nomination from
several paediatricians to evaluate the connection between emerging issues
associated with air pollution and children’s health.

NTP
scientists performed a comprehensive literature search and reviewed hundreds of
studies with potentially relevant data. Overall, they evaluated 18 human
observational studies and one animal study that specifically addressed
hypertension during pregnancy and TRAP. Usually, experimental animal data add
confidence in the conclusions; unfortunately, the limited number of animal
studies that assessed the impact of environmental exposures during pregnancy is
a research gap.

The
evaluation underwent external peer review involving experts from academia and
industry, who evaluated NTP’s draft conclusions and agreed unanimously with
NTP’s final conclusion.

The
National Toxicology Program (NTP) is a federal, inter-agency program within the U.S.
Department of Health and Human Services.

About the
National Institute of Environmental Health Sciences (NIEHS)

NIEHS affiliated to U.S. Department of Health and Human Services, supports research to understand the effects of the environment on human health and is part of the National Institutes of Health.

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