TSH reference values in the first trimester of gestation and correlation between maternal TSH and obstetric and neonatal outcomes: a prospective Brazilian study

Abstract

Objective: To define the normal range of TSH in the first trimester of gestation and to evaluate the correlation between maternal TSH and obstetric and neonatal outcomes. Subjects and methods: Prospective study. Women without known or clinically suspected thyroid disease and without risk factors for thyroid dysfunction, who became pregnant spontaneously and were initially evaluated up to week 12 of gestation, were included. Women with positive anti-thyroperoxidase antibodies, twin pregnancy, hyperemesis gravidarum, and trophoblastic disease were excluded. Results: In the 660 pregnant women, the mean, median, and 2.5 th and 97.5 th percentiles of TSH were 0.9, 0.96, 0.04 and 2.68 mIU/L, respectively. TSH was undetectable in 2%, < 0.5 mIU/L in 17.4%, > 2 mIU/L in 9.7%, > 2.5 mIU/L in 4.7%, and > 3 mIU/L in 1%. None of the women received levothyroxine or antithyroid drugs during pregnancy. In addition, there was no difference in obstetric or neonatal outcomes when women with TSH ≤ 0.1, between 0.1 and 2.5, and between 2.5 and 4 mIU/L were compared. Conclusion: In the population studied, the TSH value corresponding to the 97.5 th percentile was 2.68 mIU/L in the first trimester of gestation. Arch Endocrinol Metab. 2016;60(4):314-8

Maternal hypothyroxinemia in the first trimester of gestation and association with obstetric and neonatal outcomes and iron deficiency: a prospective Brazilian study

“…Obstetric and neonatal outcomes were compared between women with FT4 < 0.86 ng/dL and < 0.92 ng/dL and those with FT4 ≥ 0.92 ng/dL. These values correspond, respectively, to the 5 th and 10 th percentiles of FT4 concentrations obtained for the initially selected 660 TPOAb-negative women (8). We also compared women with TT4 < 7.8 ng/dL and ≥ 7.8 ng/dL.…”

“…Hypothyroxinemia was defined using three different criteria of T4 concentration. Regarding TSH, a cutoff of 2.5 mIU/l was used since it is still the most accepted value for the first trimester of gestation (2,3,(5)(6)(7) and is compatible with the normal range for our population (8). In addition, an overestimated TSH cutoff may compromise the conclusions because of the inclusion of women with subclinical hypothyroidism.…”

“…Regarding TSH, except when the assay-and population-specific references values are available, the range of 0.1 to 2.5 mIU/l has been accepted for the definition of maternal euthyroidism in the first trimester (2,3,(5)(6)(7). It is worth noting that this range does also seem to be adequate for our population (8). Iodine deficiency appears to the most important factor in the etiology of isolated hypothyroxinemia, but other factors have also been implicated, such as environmental disruptors, obesity, and iron deficiency (4).…”

“…The population studied was from the metropolitan region of Belo Horizonte (Minas Gerais, Brazil). One thousand and eighty two pregnant women who underwent prenatal exams at a clinical analysis laboratory and who had become pregnant spontaneously were initially interviewed and examined (8). Women who met the clinical criteria shown in Table 1 (n = 748) were first selected.…”

Maternal thyroid‐stimulating hormone reference ranges for first trimester screening from 11 to 14 weeks of gestation

“…The 2.5th and 97.5th percentiles of the values obtained were 0.04 and 2.68 mIU/L, respectively. TSH was measured with a chemiluminescent assay (Immulite 2000, Diagnostic Products Corporation, Los Angeles, CA, USA) . They used different analytical system, so it is difficult to compare results.…”