title: Heat and air pollution exposure as triggers of delivery: A survival analysis of population-based pregnancy cohorts in Rome and Barcelona.
abstract: BACKGROUND
  Environmental exposures have been linked to length of gestation but the question as to during which weeks of gestation pregnancies are most susceptible still remains little explored. We estimated the effect of maximum apparent temperature and air pollution levels on risk of birth by week of gestation.
  
  
  METHODS
  We analyzed two cohorts of singleton live births in Rome (2001-2010) and Barcelona (2007-2012). Maximum apparent temperature (MAT), PM10, O3 and NO2 were analyzed in the warm period (1st April-31st October). Gestational week-specific hazard ratios of giving birth associated to a 1-unit increase in exposure were estimated fitting Cox regression models adjusted for seasonality, and demographic and clinical characteristics of the mother.
  
  
  RESULTS
  We observed 78,633 births (5.5% preterm) in Rome and 27,255 (4.5% preterm) in Barcelona. The highest hazard ratios for 1°C increase in MAT were in the 22nd-26th weeks of gestation, 1.071, (95% CI 1.052-1.091) in Rome and 1.071 (95% CI 1.036-1.106) in Barcelona, and decreased to 1.032 (95% CI 1.026-1.038) and 1.033 (95% CI 1.020-1.045) at the 36th week of gestation, respectively. Similar associations and trends were observed for PM10 and NO2 after adjusting for MAT. O3 showed similar trends but weaker associations.
  
  
  CONCLUSIONS
  We found, consistently in Rome and Barcelona, an increased risk of delivery for a unit increase in MAT, PM10, NO2 and O3, especially in the second half of the second trimester, thus effectively increasing the risk of preterm and particularly early preterm birth. Results may help to increase awareness of these risks among public-health regulators and clinicians, leading to better preventive strategies.
authors.affiliation: Department of Epidemiology, Lazio Regional Health Service, Rome, Italy. Electronic address: p.schifano@deplazio.it.
authors.forename: Patrizia
authors.initials: P
authors.lastname: Schifano
authors.affiliation: Department of Epidemiology, Lazio Regional Health Service, Rome, Italy.
authors.forename: Federica
authors.initials: F
authors.lastname: Asta
authors.affiliation: Centre for Research in Environmental Epidemiology (CREAL), Barcelona, Spain; Universitat Pompeu Fabra (UPF), Barcelona, Spain; CIBER Epidemiología y Salud Pública (CIBERESP), Barcelona, Spain.
authors.forename: Payam
authors.initials: P
authors.lastname: Dadvand
authors.affiliation: Department of Epidemiology, Lazio Regional Health Service, Rome, Italy.
authors.forename: Marina
authors.initials: M
authors.lastname: Davoli
authors.affiliation: Centre for Research in Environmental Epidemiology (CREAL), Barcelona, Spain; Universitat Pompeu Fabra (UPF), Barcelona, Spain; CIBER Epidemiología y Salud Pública (CIBERESP), Barcelona, Spain.
authors.forename: Xavier
authors.initials: X
authors.lastname: Basagana
authors.affiliation: Department of Epidemiology, Lazio Regional Health Service, Rome, Italy.
authors.forename: Paola
authors.initials: P
authors.lastname: Michelozzi
mesh_terms: D000293:Adolescent; D000328:Adult; D000393:Air Pollutants / Q000009:adverse effects*; D015331:Cohort Studies; D004781:Environmental Exposure; D005260:Female; D005865:Gestational Age; D006358:Hot Temperature / Q000009:adverse effects*; D006801:Humans; D007231:Infant, Newborn; D011247:Pregnancy; D047928:Premature Birth / Q000139:chemically induced / Q000453:epidemiology*; D012307:Risk Factors; D012384:Rome / Q000453:epidemiology; D012621:Seasons; D013030:Spain / Q000453:epidemiology; D055815:Young Adult
chemical_list: D000393:Air Pollutants
keywords: Air pollutants; Birth cohorts; Gestational length; High temperature; Preterm