title: Adverse Infant Outcomes Associated with Discordant Gestational Age Estimates.
abstract: Gestational age estimation by last menstrual period (LMP) vs. ultrasound (or best obstetric estimate in the US) may result in discrepant classification of preterm vs. term birth. We investigated whether such discrepancies are associated with adverse infant outcomes.
  
  
  
  We studied singleton livebirths in the Medical Birth Registries of Norway, Sweden and Finland and US live birth certificates from 1999 to the most recent year available. Risk ratios (RR) with 95% confidence intervals (CI) by discordant and concordant gestational age estimation for infant, neonatal and post-neonatal mortality, Apgar score <4 and <7 at 5 min, and neonatal intensive care unit (NICU) admission were estimated using generalised linear models, adjusting for maternal age, education, parity, year of birth, and infant sex. Results were presented stratified by country.
  
  
  
  Compared to infants born at term by both methods, infants born preterm by ultrasound/best obstetric estimate but term by LMP had higher infant mortality risks (range of adjusted RRs 3.9 to 7.2) and modestly higher risks were obtained among infants born preterm by LMP but term by ultrasound/best obstetric estimate (range of adjusted RRs 1.6 to 1.9). Risk estimates for the other outcomes showed the same pattern. These findings were consistent across all four countries.
  
  
  
  Infants classified as preterm by ultrasound/best estimate, but term by LMP have consistently higher risks of adverse outcomes than those classified as preterm by LMP but term by ultrasound/best estimate. Compared with ultrasound/best estimate, use of LMP overestimates the proportion of births that are preterm.
authors.affiliation: Departments of Global Public Health and Primary Care, University of Bergen, Bergen, Norway.|Departments of Clinical Science, University of Bergen, Bergen, Norway.
authors.forename: Nils-Halvdan
authors.initials: NH
authors.lastname: Morken
authors.affiliation: Departments of Global Public Health and Primary Care, University of Bergen, Bergen, Norway.
authors.forename: Rolv
authors.initials: R
authors.lastname: Skjaerven
authors.affiliation: Department of Epidemiology, Rollins School of Public Health, Emory University, Atlanta, GA.
authors.forename: Jennifer L
authors.initials: JL
authors.lastname: Richards
authors.affiliation: Department of Epidemiology, Rollins School of Public Health, Emory University, Atlanta, GA.
authors.forename: Michael R
authors.identifier: 0000-0002-6372-6170
authors.initials: MR
authors.lastname: Kramer
authors.affiliation: Clinical Epidemiology Unit, T2, Department of Medicine Solna, Karolinska University Hospital, Karolinska Institutet, Stockholm, Sweden.
authors.forename: Sven
authors.initials: S
authors.lastname: Cnattingius
authors.affiliation: Clinical Epidemiology Unit, T2, Department of Medicine Solna, Karolinska University Hospital, Karolinska Institutet, Stockholm, Sweden.|Department of Clinical Science and Education, Södersjukhuset, Karolinska Institutet, Stockholm, Sweden.
authors.forename: Stefan
authors.initials: S
authors.lastname: Johansson
authors.affiliation: Information Services Department, National Institute for Health and Welfare, Helsinki, Finland.
authors.forename: Mika
authors.initials: M
authors.lastname: Gissler
authors.affiliation: Department of Obstetrics and Gynecology and Women's Health, Albert Einstein College of Medicine/Montefiore Medical Center, Bronx, NY.
authors.forename: Siobhan M
authors.initials: SM
authors.lastname: Dolan
authors.affiliation: Inserm UMR 1153, Obstetrical, Perinatal and Pediatric Epidemiology Research Team (Epopé), Center for Epidemiology and Statistics Sorbonne Paris Cité, DHU Risks in pregnancy, Paris Descartes University, Paris, France.
authors.forename: Jennifer
authors.initials: J
authors.lastname: Zeitlin
authors.affiliation: Departments of Pediatrics and of Epidemiology, Biostatistics and Occupational Health, McGill University Faculty of Medicine, Montreal, QC, Canada.
authors.forename: Michael S
authors.initials: MS
authors.lastname: Kramer
mesh_terms: D001034:Apgar Score; D001719:Birth Certificates; D000068598:Data Accuracy; D005260:Female; D005387:Finland; D005865:Gestational Age; D006801:Humans; D007223:Infant; D007226:Infant Mortality; D007234:Infant, Premature / Q000502:physiology*; D007363:Intensive Care Units, Neonatal; D008297:Male; D009664:Norway; D011247:Pregnancy; D011379:Prognosis; D018570:Risk Assessment; D013548:Sweden; D016216:Ultrasonography, Prenatal; D014481:United States
keywords: Gestational age estimation; best obstetric estimate; infant outcome; last menstrual period; ultrasound