title: Maternal BMI and preterm birth: a systematic review of the literature with meta-analysis.
abstract: OBJECTIVE
  To examine the association between high prepregnancy maternal body mass index (BMI) and the risk of preterm birth (PTB).
  
  
  METHODS
  A systematic review of the literature. We included cohorts and case-control studies published since 1968 that examined the association between BMI and PTB of all types, spontaneous (s), elective and with ruptured membranes (PPROM) in three gestational age categories: general (<37 weeks), moderate (32-36 weeks) and very (<32 weeks) PTB.
  
  
  RESULTS
  20,401 citations were screened and 39 studies (1,788,633 women) were included. Preobese (BMI, 25-29.9) and obese I (BMI, 30-34.9) women have a reduced risk for sPTB: AOR = 0.85 (95% CI: 0.80-0.92) and 0.83 (95% CI: 0.75-0.92), respectively. Their risk for moderate PTB was 1.20 (95% CI: 1.04-1.38) and 1.60 (95% CI: 1.32-1.94), respectively. Obese II women (BMI, 35-40) have an increased risk for PTB in general (AOR = 1.33, 95% CI: 1.12-1.57) moderate (AOR = 2.43, 95% CI: 1.46-4.05) and very PTB (AOR = 1.96, 95% CI: 1.66-2.31). Obese III women (BMI > 40) have an even higher risk for very PTB (AOR = 2.27, 95%CI: 1.76-2.94). High BMI does not modify the risk for PPROM and increases the risk for elective PTB.
  
  
  CONCLUSIONS
  High maternal BMI may have different effects on different types of PTB.
authors.affiliation: Department of Obstetrics, São Paulo Federal University, São Paulo, Brazil. ginecologia@terra.com.br
authors.forename: Maria Regina
authors.initials: MR
authors.lastname: Torloni
authors.forename: Ana Pilar
authors.initials: AP
authors.lastname: Betrán
authors.forename: Silvia
authors.initials: S
authors.lastname: Daher
authors.forename: Mariana
authors.initials: M
authors.lastname: Widmer
authors.forename: Siobhan M
authors.initials: SM
authors.lastname: Dolan
authors.forename: Ramkumar
authors.initials: R
authors.lastname: Menon
authors.forename: Eduardo
authors.initials: E
authors.lastname: Bergel
authors.forename: Tomas
authors.initials: T
authors.lastname: Allen
authors.forename: Mario
authors.initials: M
authors.lastname: Merialdi
mesh_terms: D015992:Body Mass Index; D005260:Female; D005322:Premature Rupture of Fetal Membranes / Q000453:epidemiology; D005865:Gestational Age; D006801:Humans; D009765:Obesity / Q000145:classification / Q000453:epidemiology*; D011247:Pregnancy; D047928:Premature Birth / Q000453:epidemiology*; D012306:Risk