title: Increase in thyroglobulin antibody and thyroid peroxidase antibody levels, but not preterm birth-rate, in pregnant Danish women upon iodine fortification.
abstract: OBJECTIVE
  The presence of thyroid antibodies in pregnancy has been associated with preterm birth. In the non-pregnant population, the implementation of the Danish iodine fortification program has increased the prevalence of thyroid antibodies. This study investigated the prevalence of thyroid peroxidase antibodies (TPOAbs) and thyroglobulin antibodies (TgAbs) in pregnant Danish women before, during and after implementation of the iodine fortification program and association with preterm birth.
  
  
  METHODS
  Comparative cohort study of 1368 pregnancies from three cohorts gathered before (1996-1998), during (2000-2003) and after (2008-2009) the iodine fortification program.
  
  
  METHODS
  In cohort 1 (n= 297), TPOAbs were measured (DYNOtest (BRAHMS)). In cohorts 2 (n= 148) and 3 (n= 923), both TPOAbs and TgAbs were measured (Kryptor immunofluorescent assay (BRAHMS)). The prevalence and effect of antibody positivity were explored using three cut-offs: TPOAbs and/or TgAbs >100 kU/L, TPOAbs and/or TgAbs >60 kU/L and TPOAbs >30 and/or TgAbs >20 kU/L. National preterm birth data were extracted from the National Birth Registry.
  
  
  RESULTS
  In the three cohorts, TPOAb levels >60 kU/L were found in 5.4, 8.1 and 12.0% (χ2(2,n= 1367) = 11.7,P= 0.003) respectively, and TPOAbs and/or TgAbs >60 kU/L in 8.1 and 16.2% in cohorts 2 and 3 respectively (χ2(2,n= 1070) = 6.5,P= 0.01). TgAb levels (>20 kU/L) had increased plenty-fold from cohort 2 to 3 (χ2(1,n= 1071) = 136.5,P< 0.001). Preterm birth occurred in 4.1% of all pregnancies with no effect from antibody positivity (TPOAbs and/or TgAbs >60 kU/L,χ2(1,n= 1039) = 0.0,P= 0.98, aOR = 1.1, 95% CI (0.4-2.7)). The national preterm birth-rate showed no increase over the same period.
  
  
  CONCLUSIONS
  Thyroid antibody positivity in Danish pregnant women has more than doubled upon the implementation of the iodine fortification program without an increase in preterm birth-rate.
authors.affiliation: Departments of Medical EndocrinologySection 2132.
authors.forename: Sofie
authors.initials: S
authors.lastname: Bliddal
authors.affiliation: Departments of Growth and Reproduction.
authors.forename: Malene
authors.initials: M
authors.lastname: Boas
authors.affiliation: Departments of Clinical BiochemistryCopenhagen University Hospital (Rigshospitalet), Copenhagen, Denmark.
authors.forename: Linda
authors.initials: L
authors.lastname: Hilsted
authors.affiliation: Department of Clinical BiochemistryHilleroed Hospital, Hilleroed, Denmark.
authors.forename: Lennart
authors.initials: L
authors.lastname: Friis-Hansen
authors.affiliation: Departments of Growth and Reproduction.|Faculty of Health and Medical SciencesUniversity of Copenhagen, Copenhagen, Denmark.
authors.forename: Anders
authors.initials: A
authors.lastname: Juul
authors.affiliation: Department of Foetal MedicineCopenhagen University Hospital (Holbaek Hospital), Holbaek, Denmark.
authors.forename: Torben
authors.initials: T
authors.lastname: Larsen
authors.affiliation: Faculty of Health and Medical SciencesUniversity of Copenhagen, Copenhagen, Denmark.|Department of ObstetricsCentre of Foetal Medicine, Copenhagen University Hospital (Rigshospitalet), Copenhagen, Denmark.
authors.forename: Ann
authors.initials: A
authors.lastname: Tabor
authors.affiliation: Faculty of Health and Medical SciencesUniversity of Copenhagen, Copenhagen, Denmark.|Department of Medicine OEndocrine Unit, Copenhagen University Hospital (Herlev Hospital), Herlev, Denmark.
authors.forename: Jens
authors.initials: J
authors.lastname: Faber
authors.affiliation: Department of Child PsychiatryCopenhagen University Hospital (Roskilde), Roskilde, Denmark.
authors.forename: Dorthe Hansen
authors.initials: DH
authors.lastname: Precht
authors.affiliation: Departments of Medical EndocrinologySection 2132.|Faculty of Health and Medical SciencesUniversity of Copenhagen, Copenhagen, Denmark.
authors.forename: Ulla
authors.initials: U
authors.lastname: Feldt-Rasmussen
mesh_terms: D000328:Adult; D001323:Autoantibodies / Q000097:blood*; D001327:Autoimmune Diseases / Q000150:complications / Q000453:epidemiology; D015331:Cohort Studies; D003718:Denmark / Q000453:epidemiology; D005260:Female; D005527:Food, Fortified; D006801:Humans; D007453:Iodide Peroxidase / Q000276:immunology*; D007455:Iodine / Q000008:administration & dosage*; D008137:Longitudinal Studies; D011247:Pregnancy; D011248:Pregnancy Complications / Q000276:immunology; D047928:Premature Birth / Q000453:epidemiology*; D011446:Prospective Studies; D013954:Thyroglobulin / Q000276:immunology*; D013959:Thyroid Diseases / Q000276:immunology
chemical_list: D001323:Autoantibodies; C006606:anti-thyroglobulin; C056626:thyroid microsomal antibodies; D013954:Thyroglobulin; D007455:Iodine; D007453:Iodide Peroxidase