title: Diagnosing gestational diabetes mellitus in the Danish National Birth Cohort.
abstract: BACKGROUND
  The Danish National Birth Cohort (DNBC) contains comprehensive information on diet, lifestyle, constitutional and other major characteristics of women during pregnancy. It provides a unique source for studies on health consequences of gestational diabetes mellitus. Our aim was to identify and validate the gestational diabetes mellitus cases in the cohort.
  
  
  METHODS
  We extracted clinical information from hospital records for 1609 pregnancies included in the Danish National Birth Cohort with a diagnosis of diabetes during or before pregnancy registered in the Danish National Patient Register and/or from a Danish National Birth Cohort interview during pregnancy. We further validated the diagnosis of gestational diabetes mellitus in 2126 randomly selected pregnancies from the entire Danish National Birth Cohort. From the individual hospital records, an expert panel evaluated gestational diabetes mellitus status based on results from oral glucose tolerance tests, fasting blood glucose and Hb1c values, as well as diagnoses made by local obstetricians.
  
  
  RESULTS
  The audit categorized 783 pregnancies as gestational diabetes mellitus, corresponding to 0.89% of the 87 792 pregnancies for which a pregnancy interview for self-reported diabetes in pregnancy was available. From the randomly selected group the combined information from register and interviews could correctly identify 96% (95% CI 80-99.9%) of all cases in the entire Danish National Birth Cohort population. Positive predictive value, however, was only 59% (56-61%).
  
  
  CONCLUSIONS
  The combined use of data from register and interview provided a high sensitivity for gestational diabetes mellitus diagnosis. The low positive predictive value, however, suggests that systematic validation by hospital record review is essential not to underestimate the health consequences of gestational diabetes mellitus in future studies.
authors.affiliation: Centre for Fetal Programming, Department of Epidemiology Research, State Serum Institute, Copenhagen, Denmark.|Department of Nutrition, Harvard TH Chan School of Public Health, Boston, MA, USA.
authors.forename: Sjurdur F
authors.initials: SF
authors.lastname: Olsen
authors.affiliation: Department of Endocrinology, Rigshospitalet University Hospital, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark.
authors.forename: Azedeh
authors.initials: A
authors.lastname: Houshmand-Oeregaard
authors.affiliation: Centre for Fetal Programming, Department of Epidemiology Research, State Serum Institute, Copenhagen, Denmark.
authors.forename: Charlotta
authors.initials: C
authors.lastname: Granström
authors.affiliation: Department of Obstetrics, Rigshospitalet Universtiy Hospital, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark.
authors.forename: Jens
authors.identifier: http://orcid.org/0000-0003-2838-2533
authors.initials: J
authors.lastname: Langhoff-Roos
authors.affiliation: Center for Pregnant Women with Diabetes, Department of Obstetrics, Rigshospitalet Universtiy Hospital, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark.
authors.forename: Peter
authors.initials: P
authors.lastname: Damm
authors.affiliation: Department of Public Health, Section for Epidemiology, University of Aarhus, Aarhus, Denmark.
authors.forename: Bodil H
authors.initials: BH
authors.lastname: Bech
authors.affiliation: Department of Endocrinology, Rigshospitalet University Hospital, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark.
authors.forename: Allan A
authors.initials: AA
authors.lastname: Vaag
authors.affiliation: Epidemiology Branch, Division of Intramural Population Health Research, Eunice Kennedy Shriver National Institute of Child Health and Human Development, Rockville, MD, USA.
authors.forename: Cuilin
authors.initials: C
authors.lastname: Zhang
mesh_terms: D015331:Cohort Studies; D003718:Denmark / Q000453:epidemiology; D016640:Diabetes, Gestational / Q000175:diagnosis* / Q000453:epidemiology; D005260:Female; D006801:Humans; D007407:Interviews as Topic; D008403:Mass Screening; D011247:Pregnancy; D011296:Prenatal Diagnosis; D012042:Registries; D012680:Sensitivity and Specificity
keywords: Danish National Patient Register; gestational diabetes mellitus; hospital records review; standardized telephone interview; validation