title: Hyperthyroidism incidence fluctuates widely in and around pregnancy and is at variance with some other autoimmune diseases: a Danish population-based study.
abstract: BACKGROUND
  Hyperthyroidism in women of reproductive age is predominantly caused by Graves' disease. Pregnancy associated changes in the immune system may influence the onset of disease, but population-based incidence rates in and around pregnancy have not been reported.
  
  
  OBJECTIVE
  The objective of the study was to estimate the incidence of maternal hyperthyroidism (defined by redeemed prescription of antithyroid drugs) in and around pregnancy and to compare this with the incidence of other autoimmune diseases such as rheumatoid arthritis (RA) and inflammatory bowel disease (IBD).
  
  
  METHODS
  This was a population-based cohort study.
  
  
  METHODS
  The study used the Danish nationwide registers.
  
  
  METHODS
  The participants were women who gave birth to singleton liveborn children in Denmark from 1999 to 2008 (n = 403,958).
  
  
  METHODS
  Incidence rates (IR) of maternal hyperthyroidism during a 4-year period beginning 2 years before and ending 2 years after the date when the mother was giving birth for the first time in the study period were measured.
  
  
  RESULTS
  Altogether 3673 women (0.9%) were identified with an onset of hyperthyroidism from 1997 to 2010, and the overall IR of maternal hyperthyroidism was 65.0/100,000/year. The IR of hyperthyroidism in and around pregnancy varied widely and was high in the first 3 months of pregnancy [incidence rate ratio (IRR) vs the remaining study period: 1.50 (95% CI 1.09-2.06)), very low in the last 3 months of pregnancy (0.26 (0.15-0.44)], and reached the highest level 7-9 months postpartum [3.80 (2.88-5.02)]. The incidence variation in and around pregnancy was different for RA and IBD.
  
  
  CONCLUSIONS
  These are the first population-based data on the incidence of hyperthyroidism in and around pregnancy. The incidence of hyperthyroidism was high in early pregnancy and postpartum, whereas such particular pattern was not observed for other diseases of autoimmune origin.
authors.affiliation: Departments of Endocrinology (S.L.A., A.C., P.L.) and Clinical Biochemistry (S.L.A.), Aalborg University Hospital, 9000 Aalborg, Denmark; Department of Clinical Medicine (S.L.A., P.L.), Aalborg University, 9000 Aalborg, Denmark; Section for Epidemiology, Department of Public Health (J.O.), Aarhus University, 8000 Aarhus, Denmark; and Department of Internal Medicine (A.C.), Silkeborg Hospital, 8600 Silkeborg, Denmark.
authors.forename: Stine Linding
authors.initials: SL
authors.lastname: Andersen
authors.forename: Jørn
authors.initials: J
authors.lastname: Olsen
authors.forename: Allan
authors.initials: A
authors.lastname: Carlé
authors.forename: Peter
authors.initials: P
authors.lastname: Laurberg
mesh_terms: D000293:Adolescent; D000328:Adult; D017668:Age of Onset; D001327:Autoimmune Diseases / Q000453:epidemiology*; D015331:Cohort Studies; D003718:Denmark / Q000453:epidemiology; D005260:Female; D006801:Humans; D006980:Hyperthyroidism / Q000453:epidemiology*; D015994:Incidence; D008875:Middle Aged; D011247:Pregnancy; D011248:Pregnancy Complications / Q000453:epidemiology*; D055815:Young Adult