title: Possibilities and considerations when merging dietary data from the world's two largest pregnancy cohorts: the Danish National Birth Cohort and the Norwegian Mother and Child Cohort Study.
abstract: OBJECTIVE
  To elucidate the research possibilities when merging data on maternal diet from the Danish National Birth Cohort (DNBC) and the Norwegian Mother and Child Cohort Study (MoBa), through comparison of (i) the methodology used for dietary assessment and (ii) the estimated intake of selected food groups in the two cohorts.
  
  
  METHODS
  Qualitative and quantitative comparison of the two dietary databases.
  
  
  METHODS
  Two national prospective pregnancy cohorts.
  
  
  METHODS
  Denmark, Norway.
  
  
  METHODS
  Comparison of food intake using food frequency questionnaires (FFQs).
  
  
  RESULTS
  The FFQs had overlapping time windows and a majority of the questions in the two FFQs were comparable. Calculation principles shared similar features, including the software used and use of global questions to calibrate intakes of different food groups. A total of 63 food groups were defined that could be compared across the two cohorts; these were further aggregated down to 31 broader groups. A comparison of food intakes (grams/d) showed 39, 74 and 141% lower daily intakes of fish, potatoes and rice, respectively, in DNBC vs. MoBa and 39, 54 and 65% higher daily intakes of milk, butter and potatoes in DNBC vs. MoBa. For most other food groups, differences in consumption data were below 20%.
  
  
  CONCLUSIONS
  The two FFQs are to a large extent compatible and substantial differences in dietary habits were observed between the two cohorts. This may strengthen studies using pooled analysis to examine diet-disease relations. This is a conclusion of great importance given the colossal and costly task involved to establish each of these two cohorts.
authors.affiliation: Centre for Fetal Programming, Department of Epidemiology Research, Statens Serum Institute, Copenhagen, Denmark; Department of Nutrition, Harvard School of Public Health, Boston, Massachusetts, USA.
authors.forename: Sjurdur F
authors.initials: SF
authors.lastname: Olsen
authors.forename: Bryndis Eva
authors.initials: BE
authors.lastname: Birgisdottir
authors.forename: Thorhallur I
authors.initials: TI
authors.lastname: Halldorsson
authors.forename: Anne Lise
authors.initials: AL
authors.lastname: Brantsaeter
authors.forename: Margaretha
authors.initials: M
authors.lastname: Haugen
authors.forename: Hanne
authors.initials: H
authors.lastname: Torjusen
authors.forename: Sesilje B
authors.initials: SB
authors.lastname: Petersen
authors.forename: Marin
authors.initials: M
authors.lastname: Strøm
authors.forename: Helle Margrete
authors.initials: HM
authors.lastname: Meltzer
mesh_terms: D015331:Cohort Studies; D016208:Databases, Factual; D003718:Denmark / Q000453:epidemiology; D004034:Diet Surveys; D002149:Energy Intake; D005260:Female; D006801:Humans; D039382:Maternal Nutritional Physiological Phenomena; D009664:Norway / Q000453:epidemiology; D015596:Nutrition Assessment; D011247:Pregnancy; D039401:Prenatal Nutritional Physiological Phenomena
keywords: Denmark; Norway; Pregnancy cohorts; diet; early nutrition programming; longitudinal epidemiology