title: The rise of multiple births in Brazil.
abstract: OBJECTIVE
  The aim of this study was to assess the rise in multiple births and its influence on trends of low birth weight (LBW) rates in Porto Alegre, Brazil.
  
  
  METHODS
  This is a registry-based study of live births from 1994 to 2005 obtained from the national live birth information system. Chi-square tests for trends were assessed for LBW and multiple birth rates. The impact of multiple births on LBW trends was assessed by sequential modelling, including year and further adjustment for multiple births. Risk factors for multiple births were assessed using the Poisson regression.
  
  
  RESULTS
  A total of 263 252 live births were studied. The LBW rate increased from 9.70% to 9.88% (p < 0.001) and the multiple birth rate rose from 1.95% to 2.53% (p < 0.001). LBW rate increased among twins, from 57.14% to 63.46% (p = 0.001). The twin birth rate rose by 24.7%, while the rate of triplets or higher-order increased by 150%. Multiple births may be responsible for 23.9% of the increase in the LBW rate over the period. Mothers with higher levels of schooling, older mothers and mothers delivering in private hospitals were more likely to deliver multiple births.
  
  
  CONCLUSIONS
  It seems that both the increase in multiple births and in the LBW among multiple births contributed to this rise in overall LBW rate.
authors.affiliation: Departamento de Pediatria e Puericultura da Faculdade de Medicina da Universidade Federal do Rio Grande do Sul, Porto Alegre, Rio Grande do Sul, Brazil.
authors.forename: Clécio
authors.initials: C
authors.lastname: Homrich da Silva
authors.forename: Marcelo Zubaran
authors.initials: MZ
authors.lastname: Goldani
authors.forename: Antônio Augusto
authors.initials: AA
authors.lastname: de Moura Silva
authors.forename: Marilyn
authors.initials: M
authors.lastname: Agranonik
authors.forename: Heloísa
authors.initials: H
authors.lastname: Bettiol
authors.forename: Marco Antônio
authors.initials: MA
authors.lastname: Barbieri
authors.forename: Roberto
authors.initials: R
authors.lastname: Rona
mesh_terms: D001938:Brazil / Q000453:epidemiology; D005260:Female; D006801:Humans; D007230:Infant, Low Birth Weight; D007231:Infant, Newborn; D009099:Multiple Birth Offspring / Q000706:statistics & numerical data*; D011247:Pregnancy; D012042:Registries; D012307:Risk Factors