title: Maternal thyroid parameters in pregnant women with different ethnic backgrounds: Do ethnicity-specific reference ranges improve the diagnosis of subclinical hypothyroidism?
abstract: OBJECTIVE
  Guidelines on the management of thyroid dysfunction during pregnancy have recently been updated and, for the diagnosis of subclinical hypothyroidism (SCH), a thyroid-stimulating hormone (TSH) upper reference limit (cut-off) of 4.0 mIU/L has been proposed when no institutional values are available. It is also suggested that serum TSH and thyroid autoimmunity (TAI) may be different according to the ethnic background of the women. We therefore determined the prevalence of TAI and SCH in pregnant women with different ethnic backgrounds and, to define SCH, we used different first trimester TSH upper reference cut-offs (institutional, ethnicity-specific, 2.5 mIU/L [Endocrine Society] and 4.0 mIU/L [American Thyroid Association]).
  
  
  METHODS
  Cross-sectional data analysis of 1683 pregnant women nested within an ongoing prospective database of pregnant women.
  
  
  METHODS
  The study was performed in a single centre in Brussels, Belgium. During the first antenatal visit, thyroid peroxidase antibodies (TPO-abs), TSH and free T4 (FT4) were measured and baseline characteristics recorded. Data from 481 women with sub-Saharan (SaBg; 28.6%), 754 North African (NaBg; 44.8%) and 448 Caucasian (CaBg; 26.6%) backgrounds were analysed. For the calculation of TSH reference ranges, women with TAI, outliers, twin and assisted pregnancies were excluded.
  
  
  RESULTS
  The prevalence of TAI was significantly lower in the SaBg group than in NaBg and CaBg groups (3.3% vs 8.6% and 11.1%; P<.001, respectively). Median TSH was significantly lower in SaBg and NaBg groups as compared with the CaBg group (1.3 and 1.4 vs 1.5 mIU/L; P=.006 and .014, respectively). The prevalence of women with SCH was comparable between all groups when 2.5 mIU/L was used as cut-off, but when 4.0 mIU/L or the institutional cut-off (3.74 mIU/L) was used, it was significantly higher in the CaBg group vs the NaBg group (5.4% vs 2.1% and 7.1% vs 3.3%, P=.008 and .013, respectively). The use of ethnicity-specific cut-offs did not change the prevalence of SCH as compared to the use of institutional cut-offs. However, when these cut-offs were used, the prevalence of SCH reduced by >70% (4.5% instead of 16.7%; P<.001) relative to the 2.5 mIU/L cut-off.
  
  
  CONCLUSIONS
  Pregnant women with a sub-Saharan African background had a lower prevalence of TAI and TSH levels as compared with women from other backgrounds. The use of ethnicity-specific TSH cut-offs in early pregnancy was not more specific for the diagnosis of SCH as compared to the use of the institutional cut-off.
authors.affiliation: Endocrine Unit, Centre Hospitalier Universitaire Saint Pierre, Université Libre de Bruxelles (ULB), Brussels, Belgium.
authors.forename: Flora
authors.initials: F
authors.lastname: Veltri
authors.affiliation: Departement of Gynecology and Obstetrics, Centre Hospitalier Universitaire Saint Pierre, Université Libre de Bruxelles (ULB), Brussels, Belgium.
authors.forename: Julie
authors.initials: J
authors.lastname: Belhomme
authors.affiliation: Endocrine Unit, Centre Hospitalier Universitaire Saint Pierre, Université Libre de Bruxelles (ULB), Brussels, Belgium.
authors.forename: Pierre
authors.initials: P
authors.lastname: Kleynen
authors.affiliation: Endocrine Unit, Centre Hospitalier Universitaire Saint Pierre, Université Libre de Bruxelles (ULB), Brussels, Belgium.
authors.forename: Lidia
authors.initials: L
authors.lastname: Grabczan
authors.affiliation: Departement of Gynecology and Obstetrics, Centre Hospitalier Universitaire Saint Pierre, Université Libre de Bruxelles (ULB), Brussels, Belgium.
authors.forename: Serge
authors.initials: S
authors.lastname: Rozenberg
authors.affiliation: Geriatric Unit, Centre Hospitalier Universitaire Saint Pierre, Université Libre de Bruxelles (ULB), Brussels, Belgium.
authors.forename: Thierry
authors.initials: T
authors.lastname: Pepersack
authors.affiliation: Endocrine Unit, Centre Hospitalier Universitaire Saint Pierre, Université Libre de Bruxelles (ULB), Brussels, Belgium.
authors.forename: Kris
authors.identifier: http://orcid.org/0000-0002-5452-4243
authors.initials: K
authors.lastname: Poppe
mesh_terms: D000328:Adult; D017954:Africa South of the Sahara / Q000208:ethnology; D000352:Africa, Northern / Q000208:ethnology; D015551:Autoimmunity; D005260:Female; D006801:Humans; D007037:Hypothyroidism / Q000175:diagnosis* / Q000208:ethnology*; D011247:Pregnancy; D012016:Reference Values; D013960:Thyroid Function Tests / Q000592:standards*; D013961:Thyroid Gland / Q000276:immunology / Q000502:physiology*; D013972:Thyrotropin / Q000097:blood* / Q000592:standards; D044465:White People; D055815:Young Adult
chemical_list: D013972:Thyrotropin
keywords: TSH reference ranges; ethnic background; hypothyroidism; pregnancy; thyroid