title: Which factors could explain the low birth weight paradox?
abstract: OBJECTIVE
  Low birth weight children are unusual among well-off families. However, in Brazil, low birth weight rate was higher in a more developed city than in a less developed one. The study objective was to find out the reasons to explain this paradox.
  
  
  METHODS
  A study was carried out in two municipalities, Ribeirão Preto (Southeastern Brazil) and São Luís (Northeastern Brazil), which low birth weight rates were 10.7% and 7.6% respectively. Data from two birth cohorts were analyzed: 2,839 newborns in Ribeirão Preto in 1994 and 2,439 births in São Luís in 1997-1998. Multiple logistic regression analysis was performed, adjusted for confounders.
  
  
  RESULTS
  Low birth weight risk factors in São Luís were primiparity, maternal smoking and maternal age less than 18 years. In Ribeirão Preto, the associated variables were family income between one and three minimum wages, maternal age less than 18 and equal to or more than 35 years, maternal smoking and cesarean section. In a combined model including both cohorts, Ribeirão Preto presented a 45% higher risk of low birth weight than São Luís. When adjusted for maternal smoking habit, the excess risk for low birth weight in Ribeirão Preto compared to São Luís was reduced by 49%, but the confidence interval was marginally significant. Differences in cesarean section rates between both cities contributed to partially explain the paradox.
  
  
  CONCLUSIONS
  Maternal smoking was the most important risk factor for explaining the difference in low birth weight between both cities. The other factors contributed little to explain the difference in low birth weight rates.
authors.affiliation: Departamento de Saúde Pública, Universidade Federal do Maranhão, São Luís, MA, Brasil. aasilva@elo.com.br
authors.forename: Antônio Augusto Moura da
authors.initials: AA
authors.lastname: Silva
authors.forename: Heloisa
authors.initials: H
authors.lastname: Bettiol
authors.forename: Marco Antonio
authors.initials: MA
authors.lastname: Barbieri
authors.forename: Luiz Gustavo Oliveira
authors.initials: LG
authors.lastname: Brito
authors.forename: Márcio Mendes
authors.initials: MM
authors.lastname: Pereira
authors.forename: Vânia Maria Farias
authors.initials: VM
authors.lastname: de Aragão
authors.forename: Valdinar Sousa
authors.initials: VS
authors.lastname: Ribeiro
mesh_terms: D001938:Brazil / Q000453:epidemiology; D002585:Cesarean Section; D004812:Epidemiologic Methods; D005260:Female; D006801:Humans; D007230:Infant, Low Birth Weight; D007231:Infant, Newborn; D008297:Male; D008423:Maternal Age; D015997:Neonatal Screening; D017678:Sex Distribution; D012907:Smoking / Q000009:adverse effects; D012959:Socioeconomic Factors