In October 2015, the American Academy of Pediatrics published a landmark technical report on the risks faced by the world’s children due to climate change.[1] The paper included the World Health Organization’s startling conclusion that “more than 88% of the existing burden of disease attributable to climate change occurs in children younger than 5 years”.
Ahdoot, S., Pacheco, S. E., & Council on Environmental Health. (2015). Global climate change and children’s health. Pediatrics, 136(5), e1468–e1484. https://doi.org/10.1542/peds.2015-3233
The implication – that so much harm would be focused on the very young – was a wake-up call for paediatricians and those who care for pregnant mothers. Was the climate crisis already endangering birth outcomes in the USA? At the time, the American College of Obstetrics and Gynecology[2]) had a position statement on climate change that noted “negative obstetric outcomes”, but no large reviews had addressed this question.
American College of Obstetrics and Gynecology. (2018). Climate change and women’s health, Position statement. https://www.acog.org/clinical-information/policy-and-position-statements/positionstatements/2018/climate-change-andwomens-health
With colleagues, we decided to explore the medical literature from 2007 onwards. We discovered a large volume of data on pregnant women’s exposure to higher temperatures and to two types of air pollution related to climate change: fine particulate matter and ozone. Our initial explorations suggested that these exposures were frequently associated with pre-term delivery, low birthweight and even stillbirth.
For the next three years we analysed this data, applying rigorous exclusion criteria to try to clarify the extent of the association. In 2019, the Journal of the American Medical Association (JAMA) put out a call for papers on climate and health.
Although pregnant women and newborns were not among the vulnerable groups they listed, we decided to submit our findings.
In early 2020, we assembled the final results and were astonished. Of the 68 papers that met our criteria, 57 (84%) found a statistically significant association between at least one of these environmental exposures and birth outcomes. These were large studies, with a mean of over 560,000 births per study and a total of 32 million US births. We found positive associations in regions across the country.
On air pollutants, 19 of the 24 studies that looke at pre-term delivery found a significant association. This was also true for 25 of the 29 studies that looked at low birthweight, and 4 of the 5 studies that looked at stillbirth. On heat exposure, 9 of the 10 studies showed similarly strong associations with each of these birth outcomes.
We could not estimate the degree of increased risk, due to the diverse methodologies used. However, the level of agreement among such heterogeneous studies is itself strong evidence for an overall connection between climate change and adverse birth outcomes. In sum, this large and growing volume of data assert that climate change, through its effects on air pollution and heat, is already threatening newborns throughout the USA.
Black mothers are especially at risk
JAMA published our study[3] on 18 June 2020, at the height of the Black Lives Matter movement in the USA. This timing resulted in wide media attention for another aspect of our findings: over half of the studies on air pollutants noted that minority mothers were at higher risk of bad birth outcomes. Black mothers were most often found to be at higher risk: they were mentioned more than twice as often as the next most mentioned group, Latinas.
Bekkar, B., Pacheco, S., Basu, R., & DeNicola, N. (2020). Association of air pollution and heat exposure with preterm birth, low birth weight, and stillbirth in the US: a systematic review. Journal of the American Medical Assoociation Network Open 3(6), e208243. https://jamanetwork.com/journals/jamanetworkopen/fullarticle/2767260
Our observation of apparent racial health disparity resonated with the previously known increased risk of black maternal mortality in the USA.[4]
National Partnership for Women & Families. (2018). Black women’s maternal health: a multifaceted approach to addressing persistent and dire health disparities, Issue brief. https://www.nationalpartnership.org/our-work/resources/health-care/maternity/black-womens-maternal-health-issue-brief.pdf
Our research was confined to studies of the US population, but other reviews that included non-US populations have found compatible results on both air pollution and heat exposures.[5][6]
Li, X., Huang, S., Jiao, A., Yang, X., Yun, J., Wang, Y., Xue, X., Chu, Y., Liu, F., Liu, Y., Ren, M., Chen, X., Li, N., Lu, Y., Mao, Z., Tian, L., & Xiang, H. (2017). Association between ambient fine particulate matter and preterm birth or term low birth weight: An updated systematic review and meta-analysis. Environmental Pollution, 227, 596–605. https://doi.org/10.1016/j.envpol.2017.03.055
Zhang, Y., Yu, C., & Wang, L. (2017). Temperature exposure during pregnancy and birth outcomes: An updated systematic review of epidemiological evidence. Environmental Pollution, 225, 700–712. https://doi.org/10.1016/j.envpol.2017.02.066
Other papers have also identified likely mechanisms by which these inputs could result in pre-term or low-birthweight infants as well as stillbirths.[7][8][9] For example, Casey et al.[10] found that when fossil fuel-powered electricity plants in California were shut down, rates of preterm delivery fell among pregnant women living nearby. This is evidence of a cause and-effect relationship, rather than a mere association. It also suggests that reducing exposures can bring nearly immediate benefits.
Saenen, N. D., Plusquin, M., Bijnens, E., Janssen, B. G., Gyselaers, W., Cox, B., Fierens, F., Molenberghs, G., Penders, J., Vrijens, K., De Boever, P., & Nawrot, T. S. (2015). In utero fine particle air pollution and placental expression of genes in the brain-derived neurotrophic factor signaling pathway: an ENVIRONAGE birth cohort study. Environmental Health Perspectives, 123(8), 834–840. https://doi.org/10.1289/ehp.1408549
He, S., Kosatsky, T., Smargiassi, A., Bilodeau-Bertrand, M., & Auger, N. (2018). Heat and pregnancy-related emergencies: risk of placental abruption during hot weather. Environment International, 111, 295–300. https://doi.org/10.1016/j.envint.2017.11.004
Iodice, S., Hoxha, M., Ferrari, L., Carbone, I. F., Anceschi, C., Miragoli, M., Pesatori, A. C., Persico, N., & Bollati, V. (2018). Particulate air pollution, blood mitochondrial DNA copy number, and telomere length in mothers in the first trimester of pregnancy: effects on fetal growth. Oxidative Medicine and Cellular Longevity, 2018, 5162905. https://doi.org/10.1155/2018/5162905
Casey, J. A., Karasek, D., Ogburn, E. L., Goin, D. E., Dang, K., Braveman, P. A., & Morello-Frosch, R. (2018). Retirements of coal and oil power plants in California: association with reduced preterm birth among populations nearby, American Journal of Epidemiology, 187(8), 1586–1594. https://doi.org/10.1093/aje/kwy110
New research published since last June echoes our findings and clarifies critical windows during pregnancy, degree of risk, and the apparent synergism between air pollution and heat, which often occur together.[11][12][13]
Qiu, X., Fong, K. C., Shi, L., Papatheodorou, S., Di, Q., Just, A., Kosheleva, A., Messerlian, C., & Schwartz, J. D. (2020). Prenatal exposure to particulate air pollution and gestational age at delivery in Massachusetts neonates 2001–2015: a perspective of causal modeling and health disparities. Environmental Epidemiology, 4(5), e113. https://doi.org/10.1097/EE9.0000000000000113
Kwag, Y., Kim, M. H., Oh, J., Shah, S., Ye, S., & Ha, E. H. (2021). Effect of heat waves and fine particulate matter on preterm births in Korea from 2010 to 2016. Environment International, 147, 106239. https://doi.org/10.1016/j.envint.2020.106239
Sexton, J., Andrews, C., Carruthers, S., Kumar, S., Flenady, V., & Lieske, S. (2021). Systematic review of ambient temperature exposure during pregnancy and stillbirth: Methods and evidence. Environmental research, 197, 111037. https://doi.org/10.1016/j.envres.2021.111037
Determining the best interventions
Looking forward, more research is urgently needed to better measure individual exposures to heat and air pollution, identify high-risk populations, and determine how best to intervene. In the USA, a bill currently before the House of Representatives[14]) would provide research funding, improve physician training to detect environmental risk factors, expand public health messaging, and provide financial assistance for those who need it, to help reduce exposures at home.
H.R. 957, a Bill to direct the Secretary of Health and Human Services to establish a grant programme to protect vulnerable mothers and babies from climate change risks, and for other purposes (the “Protecting Moms and Babies Against Climate Change Act”), introduced in the US Congress on 8 February 2020. Progress may be followed at: https://www.govtrack.us/congress/bills/117/hr957
Local-level efforts to replace fossil fuels with renewable energy for both transportation and electricity generation are likely to yield substantial public health benefits well beyond pregnancy outcomes. Efforts are underway to harness healthcare professionals as “trusted messengers” to advocate for these policies and for other measures that can reduce pregnant women’s exposure to air pollution and heat (ecoAmerica (n.d.); Medical Society Consortium on Climate & Health (n.d.)). As climate change advances, it is critical to prevent future generations from being “weakened from birth”, a process that appears to have already started.
