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• Posted October 31, 2022

Stress + Air Pollution a Bad Combo in Pregnancy: Study

Protecting pregnant women from air pollution may improve the birth weight of their babies, a new study suggests.

This is especially important for stressed-out mothers who live in neighborhoods burdened by poor air quality.

A mother-to-be's exposure to both air pollution and psychological stress during early to mid-pregnancy can disrupt delicate fetal growth, according to the study authors.

"Although air pollution has a harmful effect on many different populations, our study identified the effects on expectant mothers who are already most vulnerable,"said study co-author Zhongzheng Niu.

"The addition of high perceived stress is another factor contributing to this issue. We already know air pollution is linked to low birth weight and future disease risk. Protecting pregnant women from these risks would ultimately protect future generations,"added Niu, a postdoctoral scholar and research associate at the University of Southern California (USC) Keck School of Medicine.

Having a low birth weight increases an infant's risks of other health issues, including breathing problems, bleeding in the brain, jaundice, infections and even death. It may also increase long-term disease risks, such as diabetes, heart disease, high blood pressure, intellectual and developmental disabilities, and obesity, the research team noted in a university news release.

For the study, the researchers analyzed the issue using data from 628 predominantly low-income Hispanic women who were pregnant between 2015 and 2021. The women were part of USC's MADRES (Maternal and Developmental Risks from Environmental and Social Stressors) Center.

MADRES collected medical records and residential information during clinic visits. Participants also completed a questionnaire to gauge their perceptions of stress.

The investigators measured their neighborhood-level stressors using the CalEnviroScreen Score. This screening tool identifies neighborhoods burdened by multiple sources of pollution and population vulnerability.

About 21% of participants reported high stress levels. More than 60% lived in a neighborhood with a CalEnviroScreen Score greater than 50, which was considered high, according to the study authors.

Using data from the U.S. Environmental Protection Agency, the research team examined three components of polluted air -- PM2.5, PM10 and NO2 -- near the participants' homes.

PM2.5 pollution comes from combustion of gasoline, oil, diesel fuel and wood. PM10 can be found in dust and smoke. NO2, or nitrogen dioxide, is released when fossil fuels are burned at high temperatures.

The researchers looked at daily estimates of 24-hour average NO2 and particulate matter at each participant's residence from 12 weeks before conception through 36 weeks of pregnancy.

They found that birth weight was 9.5 grams lower for each interquartile range increase (4 µg/m3) of PM2.5 exposure during the 14- to 22-week gestational period. Mothers with high stress scores experienced greater decreases in birth weight.

Moreover, moms with high stress scores who were exposed to the highest levels of PM2.5 at four to 20 weeks delivered babies weighing 34 grams, or 1 ounce, less in birth weight. Mothers exposed to highest PM10 at nine to 14 gestational weeks delivered babies weighing 39.4 grams less, on average.

Also in that same high-stress group, exposure to NO2 from nine to 14 gestational weeks was associated with a 40.4-gram decrease in birth weight. And exposure at 33 to 36 gestational weeks saw the greatest decrease in birth weight: 117.6 grams, or 4.1 ounces.

"Despite reductions in air pollution in California, we are still seeing harmful effects of air pollutants on birth weight, a key indicator of baby's future health, in vulnerable populations,"said co-author Carrie Breton, a professor of population and public health sciences at Keck.

"The combination of stressors and pollutants is important to consider in protecting babies' health," Breton added. "Continuing to monitor air pollutants still needs to be a priority. Reducing individual and neighborhood stressors should also be a priority, particularly at the policy level."

The findings were published online Oct. 25 in JAMA Network Open.

More information

The March of Dimes has tips for managing stress during pregnancy.

SOURCE: University of Southern California, news release, Oct. 25, 2022