Recent recommendations from ATA guidelines to define the upper reference range for serum TSH in the first trimester match reference ranges for pregnant women in Rio de Janeiro

Abstract

Objectives: American Thyroid Association (ATA)'s new guidelines recommend use of populationbased trimester-specific reference range (RR) for thyrotropin (TSH) in pregnancy. The aim of this study was to determine first trimester TSH RR for a population of pregnant women in Rio de Janeiro State. Subjects and methods: Two hundred and seventy pregnant women without thyroid illness, defined by National Academy of Clinical Biochemistry, and normal iodine status were included in this sectional study. This reference group (RG) had normal median urinary iodine concentration (UIC = 219 μg/L) and negative anti-thyroperoxidase antibodies (TPOAb). Twin pregnancy, trophoblastic disease and use of drugs or supplements that influence thyroid function were excluded. In a second step, we defined a more selective reference group (SRG, n = 170) by excluding patients with thyroiditis pattern on thyroid ultrasound and positive anti-thyroglobulin antibodies. This group also had normal median UIC. At a final step, a more selective reference group (MSRG, n = 130) was defined by excluding any pregnant women with UIC < 150 µg/L. Results: In the RG, median, 2.5 th and 97.5 th percentiles of TSH were 1.3, 0.1, and 4.4 mIU/L, respectively. The mean age was 27.0 ± 5.0 and the mean body mass index was 25.6 ± 5.2 kg/m 2. In the SRG and MSRG, 2.5 th and 97.5 th percentiles were 0.06 and 4.0 (SRG) and 0.1 and 3.6 mIU/L (MSRG), respectively. Conclusions: In the population studied, TSH upper limit in the first trimester of pregnancy was above 2.5 mIU/L. The value of 3.6 mIU/L, found when iodine deficiency and thyroiditis (defined by antibodies and ultrasound characteristics) were excluded, matches recent ATA guidelines.

Thyroid‐stimulating hormone (TSH) serum levels and risk of spontaneous abortion: A prospective population‐based cohort study

“…The latest guideline of the ATA has recommended an upper limit of 2.5 mIU/L for TSH during the first trimester and 3.0 mIU/L during the second and third trimester in American and European pregnant women . Previous studies reported the reference range of TSH in Brazilian, Swiss and Indian pregnant women during the first trimester as 0.14‐3.68 mIU/L, 0.0878‐2.829 mIU/L and 0.09‐6.65 mIU/L, respectively . In two separate studies conducted in Iran, the reference range of TSH for first trimester was reported as 0.2‐3.9 mIU/L and 0.2‐4.6 mIU/L, which are wider and higher than the recommended ranges by the ATA …”

Selective case finding versus universal screening for detecting hypothyroidism in the first trimester of pregnancy: a comparative evaluation of a group of pregnant women from Rio de Janeiro

“…We considered 3.8 mIU/L as the upper reference limit, by reducing 0.5 from the upper limit of TSH for non-pregnant women, according to recent recommendations from ATA's guidelines (5). This value is similar to that found by Silva de Morais and cols.., who evaluated the TSH reference range in a group of pregnant women from Rio de Janeiro (14).…”

Method-dependent variation in TSH and FT4 reference intervals in pregnancy: A systematic review

“…The studies included a total number of 132,794 pregnant women, comprising 68,097 samples analysed by Abbott (14 studies), 15,164 by Beckman (9 studies), 30,903 by Roche (15 studies) and 21,819 by Siemens (11 studies). Nineteen studies excluded women with antibodies to either thyroid peroxidase (TPOAb) or thyroglobulin (TgAb), 13,14,17–20,22,31,33,34,36,39,41,44,45,47,51,52,55 while 24 studies did not measure TgAbs and excluded women with positive TPOAb only. 15,16,21,23–25,27–30,32,35,37,38,40,42,43,46,48–50,53,54 The median age of patients ranged from 24 to 35 years with TSH and FT4 reference intervals determined during the first, second and third trimesters in 42, 28 and 26 studies, respectively.…”