title: Spatial and temporal patterns in preterm birth in the United States.
abstract: BACKGROUND
  Despite years of research, the etiologies of preterm birth remain unclear. In order to help generate new research hypotheses, this study explored spatial and temporal patterns of preterm birth in a large, total-population dataset.
  
  
  METHODS
  Data on 145 million US births in 3,000 counties from the Natality Files of the National Center for Health Statistics for 1971-2011 were examined. State trends in early (<34 wk) and late (34-36 wk) preterm birth rates were compared. K-means cluster analyses were conducted to identify gestational age distribution patterns for all US counties over time.
  
  
  RESULTS
  A weak association was observed between state trends in <34 wk birth rates and the initial absolute <34 wk birth rate. Significant associations were observed between trends in <34 wk and 34-36 wk birth rates and between white and African American <34 wk births. Periodicity was observed in county-level trends in <34 wk birth rates. Cluster analyses identified periods of significant heterogeneity and homogeneity in gestational age distributional trends for US counties.
  
  
  CONCLUSIONS
  The observed geographic and temporal patterns suggest periodicity and complex, shared influences among preterm birth rates in the United States. These patterns could provide insight into promising hypotheses for further research.
authors.affiliation: Artificial Intelligence Center, SRI International, San Diego, California.
authors.forename: John
authors.initials: J
authors.lastname: Byrnes
authors.affiliation: Robotics Program, SRI International, Menlo Park, California.
authors.forename: Richard
authors.initials: R
authors.lastname: Mahoney
authors.affiliation: 1] Division of Neonatology, Department of Pediatrics, Stanford University School of Medicine, Stanford, California [2] March of Dimes Center for Prematurity Research at Stanford, Stanford University School of Medicine, Stanford, California.
authors.forename: Cele
authors.initials: C
authors.lastname: Quaintance
authors.affiliation: 1] Division of Neonatology, Department of Pediatrics, Stanford University School of Medicine, Stanford, California [2] March of Dimes Center for Prematurity Research at Stanford, Stanford University School of Medicine, Stanford, California.
authors.forename: Jeffrey B
authors.initials: JB
authors.lastname: Gould
authors.affiliation: 1] Division of Neonatology, Department of Pediatrics, Stanford University School of Medicine, Stanford, California [2] March of Dimes Center for Prematurity Research at Stanford, Stanford University School of Medicine, Stanford, California.
authors.forename: Suzan
authors.initials: S
authors.lastname: Carmichael
authors.affiliation: 1] Division of Neonatology, Department of Pediatrics, Stanford University School of Medicine, Stanford, California [2] March of Dimes Center for Prematurity Research at Stanford, Stanford University School of Medicine, Stanford, California.
authors.forename: Gary M
authors.initials: GM
authors.lastname: Shaw
authors.affiliation: David Geffen School of Medicine, University of California, Los Angeles, California.
authors.forename: Amy
authors.initials: A
authors.lastname: Showen
authors.affiliation: 1] Division of Neonatology, Department of Pediatrics, Stanford University School of Medicine, Stanford, California [2] March of Dimes Center for Prematurity Research at Stanford, Stanford University School of Medicine, Stanford, California.
authors.forename: Ciaran
authors.initials: C
authors.lastname: Phibbs
authors.affiliation: 1] Division of Neonatology, Department of Pediatrics, Stanford University School of Medicine, Stanford, California [2] March of Dimes Center for Prematurity Research at Stanford, Stanford University School of Medicine, Stanford, California.
authors.forename: David K
authors.initials: DK
authors.lastname: Stevenson
authors.affiliation: 1] Division of Neonatology, Department of Pediatrics, Stanford University School of Medicine, Stanford, California [2] March of Dimes Center for Prematurity Research at Stanford, Stanford University School of Medicine, Stanford, California [3] Center for Policy, Outcomes and Prevention, Center for Health Policy/Center for Primary Care and Outcomes Research, Stanford University, Stanford, California.
authors.forename: Paul H
authors.initials: PH
authors.lastname: Wise
mesh_terms: D016000:Cluster Analysis; D003710:Demography; D005865:Gestational Age; D049673:History, 20th Century; D049674:History, 21st Century; D006801:Humans; D047928:Premature Birth / Q000453:epidemiology* / Q000209:etiology / Q000266:history; D044469:Racial Groups; D014481:United States / Q000453:epidemiology