title: The attitude toward hypothyroidism during early gestation: time for a change of mind?
abstract: BACKGROUND
  The approach not to screen thyroid function of all pregnant women is mainly based on conflicting evidence of whether treatment of women with mild hypothyroidism is beneficial. However, there is consensus that all women with overt hypothyroidism (OH) and those with a thyrotropin (TSH) >10 mIU/L should be treated immediately, but data on these conditions are scarce. We assessed the prevalence of OH and a TSH >10 mIU/L during the first trimester of pregnancy.
  
  
  METHODS
  Thyroid function was assessed at 10-12 weeks gestation in 4199 Dutch Caucasian healthy pregnant women from three studies conducted in 2002, 2005, and 2013 from the same iodine sufficient area in the southeast of The Netherlands. We defined the first trimester specific cutoffs (2.5th-97.5th percentile) for TSH and free thyroxine (fT4) in thyroid peroxidase antibody (TPO-Ab) negative women in each study to determine the prevalence of women with OH and those with a TSH >10 mIU/L. We extrapolated these figures to the pregnant population of 2012 in The Netherlands, the United Kingdom, and the United States.
  
  
  RESULTS
  The prevalence of OH or a TSH >10 mIU/L in these 4199 women was 26 (0.62%) of whom 96% had (highly) elevated TPO-Ab titers. Based on the birth figures of 2012, if all pregnant women from The Netherlands, the United Kingdom or the United States were screened, the conservative annual number of cases would be 1000, 4500, and 25,000 respectively. However, the United Kingdom and parts of the United States have recently been demonstrated to be iodine deficient, which will result in even higher numbers.
  
  
  CONCLUSIONS
  Our findings show that the discussion concerning thyroid screening during pregnancy should be based on data of overt hypothyroidism in healthy pregnant women. Screening of thyroid function is not expensive because all pregnant women have a standardized blood sample test at 8-12 weeks' gestation. Positive patients largely benefit from a cheap, safe, and effective treatment.
authors.affiliation: 1 Department of Medical Health Psychology, University of Tilburg , Tilburg, The Netherlands .
authors.forename: Victor
authors.initials: V
authors.lastname: Pop
authors.forename: Maarten
authors.initials: M
authors.lastname: Broeren
authors.forename: Wilmar
authors.initials: W
authors.lastname: Wiersinga
mesh_terms: D001291:Attitude of Health Personnel; D001323:Autoantibodies / Q000097:blood; D015415:Biomarkers / Q000097:blood; D005260:Female; D005865:Gestational Age; D007722:Health Knowledge, Attitudes, Practice; D006801:Humans; D007037:Hypothyroidism / Q000097:blood / Q000175:diagnosis* / Q000208:ethnology; D009426:Netherlands / Q000453:epidemiology; D010818:Practice Patterns, Physicians' / Q000592:standards; D011237:Predictive Value of Tests; D011247:Pregnancy; D011248:Pregnancy Complications / Q000097:blood / Q000175:diagnosis* / Q000208:ethnology; D011261:Pregnancy Trimester, First / Q000097:blood; D015995:Prevalence; D013960:Thyroid Function Tests / Q000592:standards; D013972:Thyrotropin / Q000097:blood; D013974:Thyroxine / Q000097:blood; D006113:United Kingdom / Q000453:epidemiology; D014481:United States / Q000453:epidemiology; D044465:White People
chemical_list: D001323:Autoantibodies; D015415:Biomarkers; C056626:thyroid microsomal antibodies; D013972:Thyrotropin; D013974:Thyroxine