Oct. 21, 2021 -- Scientists have long known that exposure to air pollution during pregnancy increases risks for preterm birth or low birth weight. New findings suggest that pollution exposures are higher in low- and middle-income countries, especially from indoor sources.

In 2019, for example, about half the world’s population breathed household air pollution from cooking fires. In addition, 92% of the global population lived in areas in which the air quality did not meet World Health Organization recommendations.

For this latest report,published in PLOS Medicine, researchers analyzed data from 124 studies on air pollution, birth weight, and preterm birth. They wanted to be sure to distinguish exposures to indoor air pollution, which often is overlooked. (A preterm birth is defined as before 37 weeks of pregnancy; low birth weight is about 5.5 pounds, or less than 2,500 grams).

Most of the studies came from the United States, Europe, and Australia, with a scattering of findings from India, China, South America, and sub-Saharan Africa. The researchers specifically included reports from Africa and Asia because indoor fire cooking is more common in these regions.

About a third of the air pollution causing preterm birth came from the outside air, so most of it came from indoor air pollution, largely in low-income countries.

The results showed that air pollution accounted for 16% of all babies born with a low birth weight and 36% of preterm births. The findings imply that 1 out of every 3 preterm births could be prevented if air pollution exposure during pregnancy could be eliminated. The study authors estimate that about 5.9 million preterm births worldwide in 2019 could instead have been delivered at term if air pollution had been kept to levels associated with minimum risk.

In sub-Saharan African countries, for example, more than half of all preterm births (52.5%) were linked to air pollution exposure. Keeping air pollution at the lowest risk level could reduce both preterm births and the rate of low birth weight by 78% in this region, the study authors estimate.

Low birth weight and preterm birth increase the risk of death before age 1 and can have other lifelong consequences. These infants are more likely to have intellectual and developmental disabilities and other issues, such as vision, lung, or hearing problems. Asthma, digestion problems, and infections are also more common in those born preterm.

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PLOS Medicine: “Ambient and household PM2.5 pollution and adverse perinatal outcomes: A meta-regression and analysis of attributable global burden for 204 countries and territories.”

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