Study finds air pollution to be likely cause of up to 6m preterm births each year

An analysis combining the results of 108 different studies from 204 countries is the first to observe the effects of indoor and outdoor pollution on pregnancy, with mounting evidence showing air pollutants to be a cause of babies being born both underweight and too early.

Indoor pollution counts for two-thirds of the global pollution burden on pregnancies

The research, published in the journal Plos Medicine, found that pollution could be attributed to around six million preterm births and three million underweight newborns each year. Additionally, indoor pollution (from burning coal or wood) contributed to two-thirds of the global pollution burden on pregnancies in 2019 alone. The remaining third was attributed to outdoor pollution caused by motor vehicles, the burning of fossil fuels and combustion processes in factories.

The results were most prevalent in areas such as south-east Asia and sub-Saharan Africa and found that adverse effects of preterm birth and low birth weight could be reduced by 78% if pollution was reduced in these regions. However, richer countries weren’t let off the hook either, as researchers estimated that 12,000 preterm births in the US in 2019 were also related to outdoor pollution.

Rakesh Ghosh, an epidemiologist at the University of California, San Francisco and lead author of the study, explained that ‘at an individual level, indoor air pollution exposure appears to carry a much higher burden compared to outdoor levels.’

So, minimising household pollution exposure, to the extent possible, should be part of the message during prenatal care, especially where household pollution is prevalent.

Why does air pollution affect pregnancy?

According to a study published in Nature Communications, air pollution can cross from the mother’s lungs to the placenta, affecting both the placenta’s health and the fetus’s development. Air pollution can also affect the bloodstream, reaching other organs.

For this specific study, researchers analysed 108 papers on pollution from across the world for associations with gestational age at birth, reduction in birth weight, low birth weight, and premature birth.

Researchers then controlled for other risk factors such as nutrition, pregnancy weight, smoking and alcohol use and found indoor/outdoor pollution to be a leading cause of low birth weight and preterm birth. The latter of which is also known to significantly increase the risk of developing many other diseases and is the leading cause of death for children under five.

Researchers from UC San Francisco and the University of Washington were also involved in the State of Global Air report in 2020. The report took a magnifying glass to pollution and its effects on pregnancy and childbirth, finding air pollution to have contributed to the deaths of 476,000 babies in 2019.

Dr Ghosh continued: ‘The air pollution-attributable burden is enormous, yet with sufficient effort, it could be largely mitigated.’

With this new, global and more rigorously generated evidence, air pollution should now be considered a major driver of infant morbidity and mortality, not just of chronic adult diseases.