title: The risk of preterm birth across generations.
abstract: OBJECTIVE
  To examine the risk of preterm birth for mothers who themselves were born before term.
  
  
  METHODS
  Data were taken from a linked data base of birth certificates composed of two cohorts: 1) a parental cohort of women born between 1947 and 1957 and 2) their offspring born between 1970 and 1992. "Preterm mothers" were women in the parental cohort who were born at less than 37 weeks' gestation. "Term mothers" were women in the parental cohort born at or after 38 weeks' gestation. Preterm mothers and term mothers were matched for birth year, county of birth, marital status, parity, and age. Odds ratios (ORs) and 95% confidence intervals (CIs) were calculated for the risk of preterm delivery in preterm mothers. Multiple logistic regression was used to assess the interaction of concomitant variables with the risk of premature delivery.
  
  
  RESULTS
  The risk of preterm birth was significantly higher in preterm mothers than in term mothers (OR 1.18; 95% CI 1.02, 1.37). The risk increased as the gestational age at the mothers' birth decreased (less than 30 weeks'; OR 2.38; 95% CI 1.37, 4.16). The interaction between maternal age and parity increased the risk of preterm delivery at less than 34 weeks in some age and parity strata.
  
  
  CONCLUSIONS
  An increased risk of preterm delivery exists for women who themselves were born before 37 weeks' gestation. The risk is inversely correlated with the maternal gestational age at birth and is influenced by maternal age and parity.
authors.affiliation: Department of Obstetrics and Gynecology, University of Utah, School of Medicine, Salt Lake City, USA. flint.porter@hsc.utah.edu
authors.forename: T F
authors.initials: TF
authors.lastname: Porter
authors.forename: A M
authors.initials: AM
authors.lastname: Fraser
authors.forename: C Y
authors.initials: CY
authors.lastname: Hunter
authors.forename: R H
authors.initials: RH
authors.lastname: Ward
authors.forename: M W
authors.initials: MW
authors.lastname: Varner
mesh_terms: D000293:Adolescent; D000328:Adult; D005260:Female; D005865:Gestational Age; D006801:Humans; D016015:Logistic Models; D007752:Obstetric Labor, Premature / Q000453:epidemiology / Q000235:genetics*; D011247:Pregnancy; D012306:Risk