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

ABSTRACT Objective: To evaluate the association of isolated hypothyroxinemia in the first trimester with obstetric and neonatal outcomes and iron deficiency. Subjects and methods: The study was prospective. Women who had become pregnant spontaneously were initially selected. Next, anti-thyroid peroxidase antibodies (TPOAb), free T4 (FT4), total T4 (TT4), TSH, and ferritin were measured. TPOAb-positive women were excluded. The final sample consisted of 596 women with serum TSH between 0.1 and 2.5 mIU/l. Hypothyroxinemia was defined as FT4 < 0.86 ng/dL and < 0.92 ng/dL, corresponding to the 5th and 10th percentiles, respectively, and TT4 < 7.8 ng/dL. None of the pregnant women was treated with levothyroxine until the end of pregnancy. Results: The women ranged in age from 18 to 36 years, with a median gestation of 9 weeks. T4 levels were not correlated with BMI or maternal TSH. Isolated hypothyroxinemia was observed in 4.3% (FT4 < 0.86 ng/dL), 9% (FT4 < 0.92 ng/dL), and 7% (TT4 < 7.8 ng/dL) of the pregnant women. The frequencies of obstetric and neonatal outcomes were similar in women with versus without hypothyroxinemia. In women without iron deficiency, 8.4%, 3.9%, and 6.5% had FT4 < 0.92 ng/dl, FT4 < 0.86 ng/dL and TT4 < 7.8 ng/dL, respectively. These frequencies of hypothyroxinemia were significantly higher among women with iron deficiency (20.7%, 14.8% and 17.2%, respectively). Conclusions: This prospective Brazilian study found no association between isolated hypothyroxinemia in the first trimester of gestation and obstetric or neonatal outcomes, but an association was demonstrated with iron deficiency.

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 2.5th and 97.5th 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 97.5th percentile was 2.68 mIU/L in the first trimester of gestation.