Program: Abstracts - Orals, Featured Poster Presentations, and Posters
Session: MON 437-470-Non-neoplastic Thyroid Disorders
Monday, June 17, 2013: 1:45 PM-3:45 PM
Expo Halls ABC (Moscone Center)

Poster Board MON-456
Tim Korevaar*, Marco Medici, Yolande de Rijke, Willy Visser, Sabine de Muinck Keizer-Schrama, Vincent Jaddoe, Albert Hofman, Herbert Hooijkaas, Henning Tiemeier, Eric Steegers, Jacoba Bongers-Schokking, Edward Visser, Theo Visser and Robin Peeters
Erasmus Medical Center, Rotterdam
Context: Abnormal maternal thyroid function during pregnancy is associated with various complications. International guidelines advocate the use of population-based trimester-specific reference ranges for thyroid function tests. When such data are unavailable, upper TSH limits of 2.5 mU/l for the first,- and 3.0 mU/l for the second and third trimesters are recommended. Although inter-individual differences in thyroid function tests may partially be explained by ethnicity, data on the influence of ethnicity on thyroid parameters during pregnancy are sparse.

Material and methods: Serum TSH, FT4, T4 and TPO antibody (TPOAb) levels were determined during early pregnancy in 4103 pregnant women from the Generation R study. Additional data were available on maternal age, parity, smoking, socio-economic status and urinary iodine levels.

Results: The study population consisted of 2765 Dutch, 308 Moroccan, 421 Turkish and 609 Surinam/Antillean women. Urinary iodine excretion indicated that the total group and each separate ethnic group were iodine sufficient. Median TSH was higher in Dutch and Turkish women than in Moroccan or Surinamese/Antillean women (1.41-1.39 vs. 1.14-1.15 mU/l; P<0.01). Although no differences in FT4 were seen, median T4 levels were lower in Dutch women (140 vs. 151-157 nmol/l; P<0.01). Turkish women had the highest risk of TPOAb positivity (9.3% vs. 4.4-5.8%; P=0.02) and of elevated TSH levels in the second trimester according to international guidelines (13.6% vs. 5.0-9.5%;P=0.02).
A comparison of disease prevalence between a population-based versus an ethnicity-specific reference range changed the diagnosis for 19% (N=54) of all 290 women who were initially diagnosed as having an abnormal thyroid function test. Vice versa, of all 3813 women who were considered euthyroid using population-based reference ranges, 1.3% (N=54) had an abnormal thyroid function test when ethnicity-specific reference ranges were used.

Conclusions: Ethnic differences in serum TSH, T4 and TPOAb positivity within one population from one geographical area resulted in considerable misclassification of thyroid disease. It is likely that the use of fixed trimester-specific cut-offs throughout the world will result in an even larger number of misclassified patients. These data underline the importance of calculating population-based reference ranges in different regions throughout the world, which should preferably also take large local ethnic groups into account.

Nothing to Disclose: TK, MM, YD, WV, SD, VJ, AH, HH, HT, ES, JB, EV, TV, RP

*Please take note of The Endocrine Society's News Embargo Policy at

Sources of Research Support: Netherlands Organization for Health Research and Development to R.P.P. (VENI Grant 91696017 and Clinical Fellowship Grant 90700412)