Ambient air pollution implicated in millions of underweight and premature births

An update of the ‘burden of global disease’ studies has for the first time shown to what extent air pollution affects several key indicators of pregnancy, including birth weight and preterm delivery.

Air pollution probably contributed to almost 6 million premature births and almost 3 million underweight babies in 2019, according to a worldwide burden of disease study and meta-analysis quantifying the effects of indoor and outdoor ambient pollution.(1) This, say the authors, is the first assessment of how air pollution affects several key indicators of pregnancy, including gestational age at birth, reduction in birth weight, low birth weight and preterm birth. This is also the first global burden of disease study to include the effects of indoor air pollution, which accounted for two-thirds of the measured effects, mostly from cooking stoves.

Behind the study, say the authors, lies a wealth of evidence that air pollution is now a major risk factor for the burden of global disease, yet its impacts on perinatal outcomes have so far not been included in these assessments, despite more than 150 original research articles indicating the adverse effects of exposure to particulate matter (<2.5 micrometer, PM2.5) during pregnancy.

The Global Burden of Diseases, Injuries, and Risk Factors Study of 2017 (funded by the Bill and Melinda Gates Foundation) provided a widespread assessment of deaths, premature mortality and disability attributable to metabolic, environmental, occupational and behavioural risk factors.(2) Two years later this was updated and the Global Burden of Disease 2019 Study attributed 29% of the global under-5 mortality to short gestation and 34% to low birth weight.(3)

This latest updated version is a complex study based on a meta-regression analysis of more than 150 studies of risk exposure related to birth weight and preterm birth. Globally, an estimated 16% of all low birth weight and 36% of all preterm birth infants were attributable to total PM2.5. The study also found that around one-third of the total PM2.5 burden for low birth weight and preterm birth could be attributable to ambient exposure, with household air pollution (from cooking stoves) dominating in low-income countries.

As background to the study, the authors write that the WHO estimates that more than 90% of the world’s population lives with polluted outdoor air, and half the global population is also exposed to indoor air pollution from burning coal and wood inside the home. The study concluded that the global incidence of preterm birth and low birthweight could be reduced by almost 78% if air pollution were minimised in Southeast Asia and sub-Saharan Africa, where indoor pollution is common and preterm birth rates are the highest in the world.

Of course, such details from a global perspective are difficult to grasp, especially for those in reproduction clinics and labs. But closer to home there have now been many studies showing a direct association between particulate matter air pollution and several fertility parameters and/or ART outcomes. One just published found that an increase in PM10 exposure was associated with a decrease in clinical and ongoing pregnancies, while exposure below PM10 was associated with a significant increase in pregnancy rates.(4) Other studies have found associations between air pollution and AMH levels in women and sperm quantity and quality in men.

Earlier this year Focus on Reproduction reported findings from a Chinese study of more than 10,000 couples exposed to varying levels of air pollution and concluding that for every 10 microgram increase in exposure to fine particulate matter (PM2.5) the risk of infertility rose by 20%.(5) The study authors described ambient air pollution as ‘an unignorable risk factor for infertility’ – and by way of a biological explanation suggested that exposure to PM2.5 ‘may enhance follicular atresia through effects on ovarian inflammation, oxidative stress, and apoptosis, which could be a step in the pathway for the impact of PM2.5 on fecundity’.

In 2019 a report the Forum of International Respiratory Societies’ Environmental Committee reported that tissue damage may result directly from pollutant toxicity ‘because fine and ultrafine particles can gain access to organs’.(6) This proved to be the case in a study of the same year in which black carbon particles as part of combustion-derived particulate matter were found in human placentas.(7) ‘The findings,’ said the study authors, ‘suggest that ambient particulates could be transported towards the fetus and represents a potential mechanism explaining the detrimental health effects of pollution from early life onwards.’

Meanwhile, these large-scale environmental findings are a further reminder of the importance of air quality in the IVF lab. Several studies have now shown that both particulate matter and chemical pollution from volatile organic compounds adversely affect IVF results, with low levels associated with better outcomes. Systems for detection, monitoring and filtration are already applied in many IVF labs to ensure ‘cleanroom’ air quality.(8)

1. Ghosh R, Causey K, Burkart K, et al. Ambient and household PM2.5 pollution and adverse perinatal outcomes: A meta-regression and analysis of attributable global burden for 204 countries and territories. PLoS Med 2021; 18(9): e1003718. doi.org/10.1371/journal.pmed.1003718
2. Stanaway JD, Afshin A, Gakidou E et al. Global, regional, and national comparative risk assessment of 84 behavioural, environmental and occupational, and metabolic risks or clusters of risks for 195 countries and territories, 1990–2017: a systematic analysis for the Global Burden of Disease Study 2017. Lancet 2018; 392: 1923-1994. doi:10.1016/S0140-6736(18)32225-6
3. GBD 2019 Risk Factors Collaborators. Global burden of 87 risk factors in 204 countries and territories, 1990–2019: a systematic analysis for the Global Burden of Disease Study 2019. Lancet 2020; 396: 1223–149. doi.org/10.1016/S0140-6736(20)30752-2
4. Iodice S, Pagliardini L, Cantone L, et al. Association between short-term exposure to particulate matter air pollution and outcomes of assisted reproduction technology in Lombardy, Italy: A retrospective cohort study. Reprod Toxicol 2021; 105: 148-155.
doi:10.1016/j.reprotox.2021.08.008.
5. https://www.focusonreproduction.eu/article/News-in-Reproduction-Air-pollution-China
6. Schraufnagel DE, Balmes JR, Cowell CT, et al. Air pollution and noncommunicable diseases. Chest 2019; 155: 409-416.
7. Bové H, Bongaerts E, Slenders E, et al. Ambient black carbon particles reach the fetal side of human placenta. Nat Commun 2019; 10: 3866. doi.org/10.1038/s41467-019-11654-3
8. Sciroro R, Rapalini E, Esteves SC. Air quality in the clinical embryology laboratory: a mini-review. Ther Adv Reprod Health 2021; 15: 2633494121990684. doi:10.1177/2633494121990684

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