AUTHOR=Singh Tanya , Jalaludin Bin , Hajat Shakoor , Morgan Geoffrey G. , Meissner Katrin , Kaldor John , Green Donna , Jegasothy Edward 

TITLE=Acute air pollution and temperature exposure as independent and joint triggers of spontaneous preterm birth in New South Wales, Australia: a time-to-event analysis

JOURNAL=Frontiers in Public Health

VOLUME=Volume 11 - 2023

YEAR=2023

URL=https://www.frontiersin.org/journals/public-health/articles/10.3389/fpubh.2023.1220797

DOI=10.3389/fpubh.2023.1220797

ISSN=2296-2565

ABSTRACT=Exposure to high ambient temperatures and air pollution have been shown to increase the risk of spontaneous preterm birth (sPTB). Less clear are the effects of cold and the joint effects of air pollution and temperature.
Using a Cox proportional hazard regression model, we assess the risk of independent and combined short-term exposure to ambient daily mean temperature and PM2.5 associated with sPTB in the last week before delivery on overall sPTB (week 23 – 36) and three subtypes: extremely sPTB, very sPTB, and moderate-to-late sPTB for a birth cohort of 1,318,570 births from Australia (Jan 2001 – Dec 2019), while controlling for chronic exposure (i.e., throughout pregnancy except of the last week before delivery) to PM2.5 and temperature. 
Temperature was modelled as a natural cubic spline, PM2.5 as a linear term and the interaction effect was estimated using a multiplicative term. For short-term exposure to temperature hazard ratios reported are relative to the median temperature (18.1°C). Hazard ratios at low temperature (5th percentile [11.5°C]) were 0.95 (95% CI: 0.90, 1.00), 1.08 (95% CI: 0.84, 1.4), 0.87 (95% CI: 0.71, 1.06), and 1.00 (95% CI: 0.94, 1.06) and greater for high temperature (95th percentile [24.5°C]): 1.22 (95% CI: 1.16, 1.28), 1.27 (95% CI: 1.03, 1.57), and 1.26 (95% CI: 1.05, 1.5) and 1.05 (1.00, 1.11), respectively for overall, extremely, very, and moderate-to-late sPTB. While chronic exposure to PM2.5 had adverse effects on sPTB, short-term exposure to PM2.5 appeared to have a negative association with all types of sPTB, with hazard ratios ranging from 0.86 (95th CI:0.80, 0.94) to 0.98 (95th CI:0.97, 1.00) per 5 μg/m3 increase in PM2.5. Risk of sPTB was found to increase following acute exposure to hot and cold ambient temperatures. Earlier sPTB subtypes seemed to be the most vulnerable. This study adds to the evidence that short-term exposure to ambient cold and heat, and longer-term gestational exposure to ambient PM2.5 is associated with elevated risk of sPTB.