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 population-based 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, 2.5th and 97.5th percentiles of TSH were 1.3, 0.1, and 4.4 mIU/L, respectively. The mean age was 270 ± 5.0 and the mean body mass index was 25.6 ± 5.2 kg/m2. In the SRG and MSRG, 2.5th and 975th 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.

Hormona estimulante de la tiroides

La hormona estimulante de la tiroides- TSH por throid stimulating hormone-, liberada por la hipófisis anterior, es principal regulador de la función tiroidea. La secreción de la TSH es controlada por el hipotálmo mediante la hormona liberadora de tirotropina - TRH por thyrotropin releasing hormone-. A su vez, este sistemea regula la liberación de las hormonas tiroides: Tiroxina- T4- y tirotropina- T3-. En la producción de la TSH existe un mecanismo de retroalimentación negativo, que es sensible a las concentraciones de las hormonas tiroideas circulantes, T3 y T4, controladas por el hipotálamo. Colectivamente este sistema se denomina eje hipotálamo-hipofisiario-tiroideo. Cualquier alteraciónen la función del eje influye sobre los niveles sanguíneos de la T4 y T3.