title: Investigating Implausible Gestational Age and High Birthweight Combinations.
abstract: BACKGROUND
  Birth certificate data overestimate national preterm births because a high percentage of last menstrual period (LMP) dates have errors. Study goals were to determine: (i) To what extent errors in transfer of birthweight and LMP date from medical records to birth certificates contribute to implausibly high birthweight-for-gestational-age births; (ii) What percentage of implausible births would be resolved if the clinical estimate (CE) from birth certificates were used instead of LMP-based gestational age, and with what degree of certainty; and (iii) Of those not resolved, what percentage had a medical explanation.
  
  
  METHODS
  Medical records and birth certificates for all singleton infants with implausibly high birthweight-for-gestational-age based on LMP delivered in the Kaiser Permanente Northwest system in Oregon during 1998-2007 were examined. Percentages of implausible records resolved under various scenarios were calculated.
  
  
  RESULTS
  A total of 100 births with implausibly high birthweight-for-gestational age combinations were identified. When LMP date and birthweight from medical records were used instead of from birth certificates, 31% of births with implausible combinations were resolved. Substituting the CE on the birth certificate for the LMP date resolved 92%. Of the latter, the clinician's gestational age estimate in the medical record was obtained in early pregnancy in 72%. Five of the eight births with unresolved implausible combinations were to mothers with diabetes; the remaining three had no documented medical explanation.
  
  
  CONCLUSIONS
  In this study, use of the birth certificate CE rather than the LMP resulted in a clinically reliable reclassification for the majority of implausible birthweight-for-gestational age deliveries.
authors.affiliation: Centers for Disease Control and Prevention, Atlanta, GA.
authors.forename: Lucinda J
authors.initials: LJ
authors.lastname: England
authors.affiliation: Kaiser Permanente Center for Health Research, Portland, OR.
authors.forename: Joanna E
authors.initials: JE
authors.lastname: Bulkley
authors.affiliation: Centers for Disease Control and Prevention, Atlanta, GA.
authors.forename: Karen
authors.initials: K
authors.lastname: Pazol
authors.affiliation: Centers for Disease Control and Prevention, Atlanta, GA.
authors.forename: F Carol
authors.initials: FC
authors.lastname: Bruce
authors.affiliation: Kaiser Permanente Center for Health Research, Portland, OR.
authors.forename: Terry
authors.initials: T
authors.lastname: Kimes
authors.affiliation: Centers for Disease Control and Prevention, Atlanta, GA.
authors.forename: Cynthia J
authors.initials: CJ
authors.lastname: Berg
authors.affiliation: Kaiser Permanente Center for Health Research, Portland, OR.
authors.forename: Mark C
authors.initials: MC
authors.lastname: Hornbrook
authors.affiliation: Centers for Disease Control and Prevention, Atlanta, GA.
authors.forename: William M
authors.initials: WM
authors.lastname: Callaghan
mesh_terms: D000328:Adult; D001719:Birth Certificates; D001724:Birth Weight; D005260:Female; D005865:Gestational Age; D006801:Humans; D007231:Infant, Newborn; D007232:Infant, Newborn, Diseases; D007233:Infant, Postmature; D008297:Male; D008499:Medical Records; D009922:Oregon / Q000453:epidemiology; D011247:Pregnancy; D011256:Pregnancy Outcome; D047928:Premature Birth / Q000453:epidemiology*
keywords: clinical estimate; gestational age; misclassification; preterm delivery