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Preterm birth is a major global health issue that can lead to infant mortality and long-term health complications. In Australia more than 26,000 Australian babies are born preterm each year and 15 million babies globally.

Defined as a birth occurring before 37 weeks, premature birth poses challenges for healthcare systems and families. With global warming leading to more extreme heat events, understanding their impact on preterm birth is crucial. A new study led by Monash University researchers examined the association between heat exposure during pregnancy and preterm birth, considering the potential mitigating role of “greenness,” including tree cover and green spaces.

The cohort study analysed birth data from mothers in Sydney, collected as part of the New South Wales Midwives Data Collection (2000-2020), which included more than 60,000 pre-term births over that period. It focused on pregnant mothers’ exposure to extreme heat and greenness during each trimester. The researchers assessed heat exposure using meteorological data to determine patterns of exposure to certain temperatures over time, while greenness was measured by combining measures such as known vegetation in an area and tree cover data, plus the level of “urbanisation” in a given region (or how built up the area was).

The study found a significant association between exposure to extreme heat in the third trimester and increased odds of preterm birth. That meant women who were exposed to extreme temperatures in their third trimester were at a higher risk of preterm birth. Exposure to extreme temperatures in a mother’s first or second trimester did not have the same effect. Researchers also found that the presence of greenness in residential areas had some moderating effect on this association – that is, higher levels of greenness were linked to a reduced risk of preterm birth even when mothers were exposed to extreme heat.

These findings highlight an unusual association – extreme heat and premature birth – and underline the important role of urban planning and public health interventions in mitigating preterm birth risks. The authors suggest that improving strategies to increase green spaces in urban areas could be a significant step towards reducing these impacts of heat on pregnancy outcomes. It’s also another factor clinicians may look to if they have patients who already have risk factors for preterm birth and who have a third trimester that could fall in a period of extreme heat.


Further information

Heat Exposure, Preterm Birth, and the Role of Greenness in Australia: National Center for Biotechnology Information


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