Bianca Cox1, Ana M Vicedo-Cabrera2, Antonio Gasparrini3,4, Harry A Roels1,5, Evelyne Martens6, Jaco Vangronsveld1, Bertil Forsberg2, Tim S Nawrot1,7. 1. Centre for Environmental Sciences, Hasselt University, Diepenbeek, Belgium. 2. Occupational and Environmental Medicine, Department of Public Health and Clinical Medicine, Umeå University, Umeå, Sweden. 3. Department of Social and Environmental Health Research, London School of Hygiene and Tropical Medicine (LSHTM), London, UK. 4. Department of Medical Statistics, LSHTM, London, UK. 5. Louvain Centre for Toxicology and Applied Pharmacology, Université Catholique de Louvain, Brussels, Belgium. 6. Study Centre for Perinatal Epidemiology, Brussels, Belgium. 7. Department of Public Health and Primary Care, Leuven University, Leuven, Belgium.
Abstract
BACKGROUND: Recent evidence suggests that elevated ambient temperatures may trigger preterm delivery. Since results from studies in temperate climates are inconclusive, we investigated the association between temperature and the risk of preterm birth in Flanders (Belgium). METHODS: We used data on 807 835 singleton deliveries (January 1998-July 2011). We combined a quasi-Poisson model with distributed lag non-linear models to allow for delayed and non-linear temperature effects, accounting for the daily pregnancies at risk and their gestational age distribution. RESULTS: For moderate heat (95th vs 50th centile) up to 1 day before delivery (lag 0-1), the risk of preterm birth increased by 8.5% (95% CI 2.4% to 15.0%) when minimum temperature increased from 8.3°C to 16.3°C and by 9.6% (95% CI 1.1% to 18.7%) when maximum temperature increased from 14.7°C to 26.5°C. Corresponding estimates for extreme heat (99th vs 50th centile) were 15.6% (95% CI 4.8% to 27.6%) for minimum temperature (19.0°C vs 8.3°C) and 14.5% (95% CI 0.5% to 30.6%) for maximum temperature (30.7°C vs 14.7°C). Despite the increased risk of preterm birth associated with cold at lag 2 (and lag 1 for minimum temperature), cumulative cold effects were small. The per cent change in preterm birth associated with moderate cold (5th vs 50th centile) up to 3 days before delivery (lag 0-3) was 2.1% (95% CI -4.1% to 8.7%) for minimum temperature (-2.0°C vs 8.3°C) and 0.6% (95% CI -7.3% to 9.2%) for maximum temperature (2.5°C vs 14.7°C). CONCLUSIONS: Even in a temperate climate, ambient temperature may trigger preterm delivery, suggesting that pregnant women should avoid temperature extremes. Published by the BMJ Publishing Group Limited. For permission to use (where not already granted under a licence) please go to http://www.bmj.com/company/products-services/rights-and-licensing/.
BACKGROUND: Recent evidence suggests that elevated ambient temperatures may trigger preterm delivery. Since results from studies in temperate climates are inconclusive, we investigated the association between temperature and the risk of preterm birth in Flanders (Belgium). METHODS: We used data on 807 835 singleton deliveries (January 1998-July 2011). We combined a quasi-Poisson model with distributed lag non-linear models to allow for delayed and non-linear temperature effects, accounting for the daily pregnancies at risk and their gestational age distribution. RESULTS: For moderate heat (95th vs 50th centile) up to 1 day before delivery (lag 0-1), the risk of preterm birth increased by 8.5% (95% CI 2.4% to 15.0%) when minimum temperature increased from 8.3°C to 16.3°C and by 9.6% (95% CI 1.1% to 18.7%) when maximum temperature increased from 14.7°C to 26.5°C. Corresponding estimates for extreme heat (99th vs 50th centile) were 15.6% (95% CI 4.8% to 27.6%) for minimum temperature (19.0°C vs 8.3°C) and 14.5% (95% CI 0.5% to 30.6%) for maximum temperature (30.7°C vs 14.7°C). Despite the increased risk of preterm birth associated with cold at lag 2 (and lag 1 for minimum temperature), cumulative cold effects were small. The per cent change in preterm birth associated with moderate cold (5th vs 50th centile) up to 3 days before delivery (lag 0-3) was 2.1% (95% CI -4.1% to 8.7%) for minimum temperature (-2.0°C vs 8.3°C) and 0.6% (95% CI -7.3% to 9.2%) for maximum temperature (2.5°C vs 14.7°C). CONCLUSIONS: Even in a temperate climate, ambient temperature may trigger preterm delivery, suggesting that pregnant women should avoid temperature extremes. Published by the BMJ Publishing Group Limited. For permission to use (where not already granted under a licence) please go to http://www.bmj.com/company/products-services/rights-and-licensing/.
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