title: Gestation specific reference intervals for thyroid function tests in pregnancy.
abstract: BACKGROUND
  Thyroid function tests are frequently assessed during pregnancy to evaluate thyroid dysfunction or to monitor pre-existing thyroid disease. However, using non-pregnant reference intervals can lead to misclassification. International guidelines recommended that institutions should calculate their own pregnancy-specific reference intervals for free thyroxine (FT4), free triiodothyronine (FT3) and thyroid-stimulating hormone (TSH). The objective of this study is to establish gestation-specific reference intervals (GRIs) for thyroid function tests in pregnant Turkish women and to compare these with the age-matched non-pregnant women.
  
  
  METHODS
  Serum samples were collected from 220 non-pregnant women (age: 18-48), and 2460 pregnant women (age: 18-45) with 945 (39%) in the first trimester, 1120 (45%) in the second trimester, and 395 (16%) in the third trimester. TSH, FT4 and FT3 were measured using the Abbott Architect i2000SR analyzer.
  
  
  RESULTS
  GRIs of TSH, FT4 and FT3 for first trimester pregnancies were 0.49-2.33 mIU/L, 10.30-18.11 pmol/L and 3.80-5.81 pmol/L, respectively. GRIs for second trimester pregnancies were 0.51-3.44 mIU/L, 10.30-18.15 pmol/L and 3.69-5.90 pmol/L. GRIs for third trimester pregnancies were 0.58-4.31 mIU/L, 10.30-17.89 pmol/L and 3.67-5.81 pmol/L. GRIs for TSH, FT4 and FT3 were different from non-pregnant normal reference intervals.
  
  
  CONCLUSIONS
  TSH levels showed an increasing trend from the first trimester to the third trimester, whereas both FT4 and FT3 levels were uniform throughout gestation. GRIs may help in the diagnosis and appropriate management of thyroid dysfunction during pregnancy which will prevent both maternal and fetal complications.
authors.forename: Süleyman
authors.initials: S
authors.lastname: Akarsu
authors.forename: Filiz
authors.initials: F
authors.lastname: Akbiyik
authors.forename: Eda
authors.initials: E
authors.lastname: Karaismailoglu
authors.forename: Zeliha Gunnur
authors.initials: ZG
authors.lastname: Dikmen
mesh_terms: D000293:Adolescent; D000328:Adult; D005260:Female; D006801:Humans; D008875:Middle Aged; D011247:Pregnancy / Q000097:blood / Q000502:physiology*; D011261:Pregnancy Trimester, First / Q000097:blood / Q000502:physiology; D011262:Pregnancy Trimester, Second / Q000097:blood / Q000502:physiology; D011263:Pregnancy Trimester, Third / Q000097:blood / Q000502:physiology; D012016:Reference Values; D013960:Thyroid Function Tests / Q000379:methods* / Q000592:standards; D013961:Thyroid Gland / Q000502:physiology*; D013972:Thyrotropin / Q000097:blood; D013974:Thyroxine / Q000097:blood; D014284:Triiodothyronine / Q000097:blood; D014421:Turkey; D055815:Young Adult
chemical_list: D014284:Triiodothyronine; D013972:Thyrotropin; D013974:Thyroxine