Effects of high and low temperature and air pollution on the risk of preterm births. A cohort study, Rome 2001-2010

Abstract

Background Preterm births represent about 10% of total births and the first cause of perinatal mortality and morbidity in developed countries. Aims To evaluate the effect of short term exposure to high and low temperatures and air pollution on preterm delivery. Moreover to identify maternal risk factors enhancing individual susceptibility. Methods All singleton live-births in Rome between 2001-2010 were analyzed. Preterms were defined as births between the 22nd and the 36th week of gestational age. Cold (Nov to Mar) and warm (Apr to Oct) season were studied using daily minimum temperature (MT) in the first and maximum apparent temperature (MAT) and heat waves (HW) in the second. PM10, O3 and NO2 were also analyzed by season. Shape and lag dimension of the temperature-preterm relationship was tested. A Poisson GAM model was used for effect estimation, controlling for seasonal and long-term trends, day of the week, holidays. Socio-demographic and clinical risk factors were analyzed. Results Study population was of 132,691 total births, 5.5% of which preterm. A linear relationship with lag 0-2 was observed with MAT in summer, while no effect of MT was observed in winter at any lag. An increase of 1,7% (IC 95%: 0.67 -2.64) in daily preterm births per 1°C increase in MAT was estimated. Older women, with higher education level and those with obstetric or chronic pathologies reported during delivery had a lower risk while women with a chronic disease in the two years before delivery and mothers <20yrs showed a higher risk (%change 7.09; IC95% 1.42-13.08; and 2.99; IC95% 0.11-5.95 respectively). We observed a 17% increase in preterm births during HW days. Air pollutants showed no effect on preterm births, and didn’t act as confounders and effect modifiers of temperature-preterm relationship. Conclusion Prevention measures targeted to pregnant women during high temperatures should be introduced, to reduce the risk of preterm birth and the consequent adverse health conditions among preterm children.