title: Association between preterm birth and its subtypes and maternal sociodemographic characteristics during the post-transitional phase in a developing country with a very high human development index.
abstract: OBJECTIVE
  Chile is a post-transitional country evolving towards a stationary population pyramid, which may be associated with increasing preterm birth (PTB) rates. This study aimed to compare maternal sociodemographic characteristics between the start of the post-transition phase (1994) and an established stage (2013) and to evaluate associations between these characteristics and PTB.
  
  
  METHODS
  An observational analytic design was conducted using national birth records (n = 4,956,311).
  
  
  METHODS
  Variables analysed in the 20 birth cohorts from 1994 to 2013 were: length of gestation (preterm <37 weeks) subdivided by gestational age (extreme, moderate/severe and late); maternal age (≤19, 20-35 and >35 years); education level (<8, 8-12 and >12 years of education); employment; marital status; area of residence; and type of birth (singleton, twins, and triplets or higher order). The prevalence of PTB was expressed as a percentage, and associations between PTB and predictor variables were analysed using logistic regression models.
  
  
  RESULTS
  Education level, age >35 years, maternal employment, unmarried status, twin delivery and urban residency rates increased between 1994 and 2013. According to the adjusted models, age >35 years and delivery of more than two foetuses were risk factors for all PTB subtypes. Maternal employment was a risk factor for moderate/severe, late and total PTB, and a low level of education was a risk factor for late and total PTB. On the other hand, age ≤19 years was protective against all PTB subtypes.
  
  
  CONCLUSIONS
  All maternal characteristics changed between 1994 and 2013. Furthermore, the prevalence of PTB increased for all predictor variables studied over this period.
authors.affiliation: Department of Women and Newborn Health Promotion, Faculty of Medicine, University of Chile, Santiago, Chile. Electronic address: marcelaaraya@med.uchile.cl.
authors.forename: B M
authors.initials: BM
authors.lastname: Araya
authors.affiliation: Department of Women and Newborn Health Promotion, Faculty of Medicine, University of Chile, Santiago, Chile.
authors.forename: M
authors.initials: M
authors.lastname: Díaz
authors.affiliation: Department of Women and Newborn Health Promotion, Faculty of Medicine, University of Chile, Santiago, Chile.
authors.forename: D
authors.initials: D
authors.lastname: Paredes
authors.affiliation: Department of Women and Newborn Health Promotion, Faculty of Medicine, University of Chile, Santiago, Chile.
authors.forename: J
authors.initials: J
authors.lastname: Ortiz
mesh_terms: D000293:Adolescent; D000328:Adult; D002677:Chile / Q000453:epidemiology; D015331:Cohort Studies; D003906:Developing Countries; D005260:Female; D006801:Humans; D007231:Infant, Newborn; D009035:Mothers / Q000706:statistics & numerical data*; D011247:Pregnancy; D047928:Premature Birth / Q000453:epidemiology*; D015995:Prevalence; D012307:Risk Factors; D012959:Socioeconomic Factors; D055815:Young Adult
keywords: Extremely premature infant; Health transition; Population characteristics; Preterm birth; Stationary population