title: Registration of Down syndrome in the Medical Birth Registry of Norway: validity and time trends.
abstract: OBJECTIVE
  To validate Down syndrome registration in the Medical Birth Registry of Norway (MBRN), 2001-2005, and study time trends and geographical differences in Down syndrome prevalence,1967-2005.
  
  
  METHODS
  Population-based cohort study, Norway.
  
  
  METHODS
  2.3 million pregnancies and births registered in the MBRN, 1967-2005.
  
  
  METHODS
  We linked data from the MBRN during 2001-2005 with data from Norway's four laboratories of medical genetics. We calculated sensitivity and positive predictive values (PPV) of the MBRN registration overall, and by background variables. Prevalence rates from 1967 to 2005, overall and regional, were presented graphically as smoothed lowess estimates, crude and standardized for maternal age. Time trends were evaluated, adjusting for maternal age by logistic regression.
  
  
  METHODS
  Sensitivity, PPV, and prevalence rates.
  
  
  RESULTS
  Five hundred and seventy-six verified cases of Down syndrome gave a prevalence of 2.0 per 1,000 among 288,213 births and terminations in the MBRN during 2001-2005. Of verified cases, 470 (81.6%) were registered with Down syndrome in the MBRN, while 470 (90.2%) of 521 MBRN-registered cases were verified. Sensitivity was higher in the Northern (93.1%; p=0.005) and Middle (90.6%; p=0.02) region relative the Southern (76.3%), higher for mothers > or =35 years (92.9%) than younger ones (86.1%; p=0.01), and higher for live births (88.8%) relative stillbirths (55.6%; p<0.001). When adjusting for maternal age, there were no significant time trends in prevalence rates from 1967 to 2005. Regional differences over time were found, probably representing reporting differences.
  
  
  CONCLUSIONS
  Validity of registration in the MBRN was satisfactory during 2001-2005. Increasing prevalence rates over time were explained by increasing maternal age.
authors.affiliation: Department of Public Health and Primary Health Care, University of Bergen, Bergen, Norway. kari.melve@isf.uib.no
authors.forename: Kari Klungsøyr
authors.initials: KK
authors.lastname: Melve
authors.forename: Rolv Terje
authors.initials: RT
authors.lastname: Lie
authors.forename: Rolv
authors.initials: R
authors.lastname: Skjaerven
authors.forename: Carl Birger
authors.initials: CB
authors.lastname: Van Der Hagen
authors.forename: Gyri Aasland
authors.initials: GA
authors.lastname: Gradek
authors.forename: Christopher
authors.initials: C
authors.lastname: Jonsrud
authors.forename: Geir J
authors.initials: GJ
authors.lastname: Braathen
authors.forename: Lorentz M
authors.initials: LM
authors.lastname: Irgens
mesh_terms: D000328:Adult; D001723:Birth Rate / Q000639:trends*; D016000:Cluster Analysis; D004314:Down Syndrome / Q000175:diagnosis / Q000453:epidemiology*; D005260:Female; D006801:Humans; D007231:Infant, Newborn; D008297:Male; D008423:Maternal Age; D009664:Norway / Q000453:epidemiology; D015995:Prevalence; D012042:Registries; D012044:Regression Analysis; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity