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Prenatal pollution exposure linked to cognitive impairment

Mothers-to-be know that, in order to give their child the best start in life, they need to follow some basic guidelines while pregnant. Eating a healthy diet is important, along with avoiding alcohol, caffeine and fish that may be contaminated with mercury. They should also keep hydrated and get enough sleep. 

Now, a new study, led by scientists from the University of Colorado, Boulder has added another word of caution; expectant mothers should also avoid exposure to air pollution during the later stages of pregnancy. Previous research has shown that exposure to high levels of ambient air pollution during pregnancy is associated with impaired neurodevelopment in pre-schoolers and school-aged children. This latest research, however, investigates whether this link also applies to brain development during a child’s earliest years. 

In the study, data were collected from 161 healthy Latino mother-infant pairs from the Southern California Mother’s Milk Study. Participants provided detailed histories of where they had lived during the pregnancy, and the researchers then used the U.S. Environmental Protection Agency’s Air Quality System, which records data from ambient monitoring stations around the country, to calculate the mothers’ likely exposure to pollutants from roadside traffic, industry, wildfire smoke and other sources. 

The scientists considered exposure to nitrogen dioxide (NO2) and particulate matter smaller than 2.5 and 10 microns in diameter (PM2.5 and PM10, respectively). They also divided the gestation period into early, mid and late, which aligned with the first, second and third trimester of pregnancy. At the age to two, the toddlers’ neurodevelopment was assessed using the Bayley-III Scales of Infant and Toddler Development, which measured cognitive, motor and language skills.

The results of the analysis, published in the journal Environmental Health, showed that two-year-olds who had been exposed prenatally to higher levels of inhalable particulate matter (both PM2.5 and PM10) scored significantly lower on cognitive tests. This was after taking into consideration differences in socioeconomic status, number of times the baby was breastfed per day, whether the infant was early, late or on time, the mother’s weight, the baby’s birthweight and other factors that could influence the results. 

For those infants exposed to PM10 levels at the 75th percentile compared to the 25th percentile, the scores were about 3 points lower on the cognitive tests. Put another way, 16 percent of participants had a composite cognitive score that indicated some degree of impairment. If all participants had been exposed to as much pollution as the 75th percentile, the prevalence of cognitive impairment at age two would be 22 percent.

Furthermore, exposure to higher PM10 levels during mid- and late-pregnancy was also correlated with lower scores on language and motor tests in the children, when they were two years of age.

“Our findings suggest that pollution exposure, particularly during mid- to late-pregnancy, may negatively impact neurodevelopment in early life,” said senior author Professor Tanya Alderete.

The study is among the first to assess the link between prenatal pollution exposure and brain development in infancy, and it adds to a growing body of evidence suggesting that exposure to dirty air during critical windows of development can have potentially lasting impacts on children’s health. This study found that prenatal exposure to air pollution was particularly detrimental to brain development if it occurred in the latter half of the pregnancy.

“The brain develops differently at different stages of pregnancy and when you have a disruption at a critical window, that can affect the trajectory of that development,” said first author Zach Morgan. He explained that during mid- to late-pregnancy, key circuits within the brain form to support sensory, communication and motor systems.

While it is not yet understood just how pollution impacts the developing brain, some previous research has suggested that inhaled pollutants may come into direct contact with the fetus, causing systemic inflammation and oxidative stress that can interfere with neurodevelopment. Other studies have found associations between prenatal exposure to pollutants and reductions in white matter, cortex thickness and blood flow in the brain as well as lower IQ scores.

The World Health Organization estimates that more than 90 percent of the world’s population is exposed to particulate matter levels that exceed its recommended levels for healthy air, and this raises concern about the health of children all over the world, and their future functional impairment.  

According to Professor Alderete, the burden of exposure is often higher among racial and ethnic minorities and low-income populations. (One EPA study found that racial minorities are exposed to as much as 1.5 times more airborne pollutants than their white counterparts). Additionally, other research by Professor Alderete has shown that Latinos in Southern California tend to live in adverse environmental conditions, including those that have been linked with poor neurodevelopmental outcomes.

“Our findings highlight the importance of addressing the impact of pollution on disadvantaged communities and point to additional steps all families can take to protect their health.”

Although Professor Alderete stresses that prenatal exposure to high levels of pollution does not automatically mean the child will have lasting cognitive deficits, she does recommend that pregnant women avoid contact with airborne pollutants whenever possible, particularly in the second and third trimesters. For example, they should not exercise outdoors on high-pollution days, and should invest in an air filtration system for inside the home. Opening the windows and steering clear of secondhand smoke are also actions that will help lower the unborn child’s exposure to air pollutants. 

“This is just one of the many things parents-to-be should be aware of to give their child the best start possible,” said Professor Alderete.

By Alison Bosman, Staff Writer

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