title: A case-control study of preterm delivery risk factors according to clinical subtypes and severity.
abstract: OBJECTIVE
  To examine risk factors of preterm delivery (PTD) among Thai women.
  
  
  METHODS
  Our case-control study included 467 term controls and 467 PTD cases. PTD was studied in aggregate and in subgroups (i.e. spontaneous preterm labor and delivery [SPTD], preterm premature rupture of membrane [PPROM], medically indicated preterm delivery [MIPTD], moderate preterm delivery [32-36 weeks], and very preterm delivery [<32 weeks]). We used multivariable logistic regression procedures to estimate odds ratio (OR) and 95% confidence intervals (CI) of potential PTD risk factors.
  
  
  RESULTS
  Advanced maternal age (>or=35 years) was associated with a 2.27-fold increased PTD risk overall (95%CI: 1.40, 3.68); and with a 3.79-fold increased risk of MIPTD (95%CI: 1.89, 7.59). Young maternal age (<20 years) was associated with a 2.07-fold increased risk of SPTD (95%CI: 1.19, 3.61). Prior history of PTD was associated with a 3.64-fold increased PTD risk overall (95%CI: 1.87, 7.09), and with a 5.69-fold increased risk of MIPTD (95%CI: 2.44, 13.24). No prenatal care was associated with all PTD subtypes. Lean women (body mass index < 18.5 kg/m(2)), compared with normal weight women (18.5-24.9 kg/m(2)), had a 1.70-fold increased risk of PTD (95%CI: 1.21, 2.39). Risk of SPTD (OR = 2.16, 95%CI: 1.44, 3.24) and very PTD (OR = 2.45, 95%CI: 1.35, 4.45) were also elevated in lean women.
  
  
  CONCLUSIONS
  Maternal age, pre-pregnancy body mass index, prior history of PTD and no utilization of prenatal care were covariates identified in this study as risk factors for PTD. Our findings also suggest heterogeneity in risk factors for clinical subtypes of PTD.
authors.affiliation: Department of Epidemiology, University of Washington School of Public Health and Community Medicine, Seattle, Washington, USA.
authors.forename: Marisa
authors.initials: M
authors.lastname: Ip
authors.forename: Elmera
authors.initials: E
authors.lastname: Peyman
authors.forename: Vitool
authors.initials: V
authors.lastname: Lohsoonthorn
authors.forename: Michelle A
authors.initials: MA
authors.lastname: Williams
mesh_terms: D000293:Adolescent; D000328:Adult; D015992:Body Mass Index; D016022:Case-Control Studies; D005260:Female; D005322:Premature Rupture of Fetal Membranes; D006801:Humans; D008423:Maternal Age; D007752:Obstetric Labor, Premature; D011247:Pregnancy; D011248:Pregnancy Complications; D047928:Premature Birth; D011295:Prenatal Care; D012307:Risk Factors; D012720:Severity of Illness Index; D013785:Thailand; D055815:Young Adult