title: Parity and 11-Year Serum Thyrotropin and Thyroid Autoantibody Change: A Longitudinal Population-Based Study.
abstract: BACKGROUND
  A role for female reproductive factors in the pathogenesis of thyroid autoimmunity has been suggested. This study investigated the prospective association between parity, abortion, use of oral contraceptive pill (OCP), and use of hormone replacement therapy (HRT), and 11-year change in serum thyrotropin (TSH), as well as change in thyroid peroxidase autoantibody (TPOAb) status.
  
  
  METHODS
  A random sample of 4649 people aged 18-65 years participated in a population-based study in the period 1997-1998. In the study presented here, 1749 non-pregnant women with no history of thyroid disease were included who participated in the 11-year follow-up examination in the period 2008-2010. Gynecological exposures were reported in a self-administered questionnaire at baseline and follow-up. TSH and TPOAb were measured at baseline and follow-up. Increased TPOAb status during follow-up was defined as a TPOAb below the assay cutoff (<30 kIU/L) at baseline and a TPOAb ≥30 kIU/L at follow-up. Multiple linear regression models were used, adjusted for age, smoking status, and urinary iodine excretion.
  
  
  RESULTS
  An inverse association was found between the number of years on HRT and the risk (odds ratio) of increased TPOAb status during follow-up (0.735 [confidence interval 0.558-0.968], p = 0.03). However, this association was not statistically significant when applying the Bonferroni adjusted significance level. The remaining reproductive factors showed no statistically significant association with risk of increased TPOAb during follow-up. Furthermore, parity, abortions, use of OCP, HRT use, age at menarche, and being pre- or postmenopausal were not significantly associated with 11-year TSH change.
  
  
  CONCLUSIONS
  No statistically significant association was found between the studied female reproductive measures and 11-year risk of TSH or TPO change. A possible protective role for HRT in the etiology of thyroid autoimmunity, however, deserves further research.
authors.affiliation: 1 Research Centre for Prevention and Health , The Capital Region of Denmark, Glostrup, Denmark .|2 Department of Endocrinology, Bispebjerg University Hospital , Copenhagen, Denmark .
authors.forename: Lena
authors.initials: L
authors.lastname: Bjergved
authors.affiliation: 3 Department of Endocrinology, Aalborg University Hospital , Aalborg, Denmark .
authors.forename: Allan
authors.initials: A
authors.lastname: Carlé
authors.affiliation: 1 Research Centre for Prevention and Health , The Capital Region of Denmark, Glostrup, Denmark .|4 Faculty of Health Sciences, University of Copenhagen , Copenhagen, Denmark .|5 Faculty of Medicine, Aalborg University , Aalborg, Denmark .
authors.forename: Torben
authors.initials: T
authors.lastname: Jørgensen
authors.affiliation: 2 Department of Endocrinology, Bispebjerg University Hospital , Copenhagen, Denmark .
authors.forename: Hans
authors.initials: H
authors.lastname: Perrild
authors.affiliation: 3 Department of Endocrinology, Aalborg University Hospital , Aalborg, Denmark .|5 Faculty of Medicine, Aalborg University , Aalborg, Denmark .
authors.forename: Peter
authors.initials: P
authors.lastname: Laurberg
authors.affiliation: 3 Department of Endocrinology, Aalborg University Hospital , Aalborg, Denmark .
authors.forename: Anne
authors.initials: A
authors.lastname: Krejbjerg
authors.affiliation: 6 Department of Gastroenterology, Slagelse Hospital , Slagelse, Denmark .
authors.forename: Lars
authors.initials: L
authors.lastname: Ovesen
authors.affiliation: 3 Department of Endocrinology, Aalborg University Hospital , Aalborg, Denmark .
authors.forename: Inge
authors.initials: I
authors.lastname: Bülow Pedersen
authors.affiliation: 7 Department of Nutrition, National Food Institute, Technical University of Denmark , Søborg, Denmark .
authors.forename: Lone Banke
authors.initials: LB
authors.lastname: Rasmussen
authors.affiliation: 2 Department of Endocrinology, Bispebjerg University Hospital , Copenhagen, Denmark .
authors.forename: Nils
authors.initials: N
authors.lastname: Knudsen
mesh_terms: D000028:Abortion, Induced; D000293:Adolescent; D000328:Adult; D000368:Aged; D001323:Autoantibodies / Q000097:blood* / Q000737:chemistry; D001324:Autoantigens / Q000097:blood; D003276:Contraceptives, Oral / Q000627:therapeutic use; D003718:Denmark; D005260:Female; D006801:Humans; D007453:Iodide Peroxidase / Q000097:blood / Q000276:immunology; D007455:Iodine / Q000008:administration & dosage; D033862:Iron-Binding Proteins / Q000097:blood; D008137:Longitudinal Studies; D008875:Middle Aged; D016017:Odds Ratio; D010298:Parity; D011247:Pregnancy; D012044:Regression Analysis; D017673:Sodium Chloride, Dietary; D013961:Thyroid Gland / Q000276:immunology*; D013972:Thyrotropin / Q000097:blood*; D013997:Time Factors; D016896:Treatment Outcome; D055815:Young Adult
chemical_list: D001323:Autoantibodies; D001324:Autoantigens; D003276:Contraceptives, Oral; D033862:Iron-Binding Proteins; D017673:Sodium Chloride, Dietary; D013972:Thyrotropin; D007455:Iodine; C056658:TPO protein, human; D007453:Iodide Peroxidase