Reference Intervals of Thyroid Hormones and Correlation of BMI with Thyroid Function in Healthy Zhuang Ethnic Pregnant Women

Abstract

Ethnic differences in the level of thyroid hormones exist among individuals. The American Thyroid Association (ATA) recommends that an institution or region should establish a specific thyroid hormone reference value for each stage of pregnancy. To date, a limited number of studies have reported the level of thyroid hormones in Chinese minorities, and the exact relationship between BMI and thyroid function in pregnant women is ill. This study was performed to establish trimester-specific reference ranges of thyroid hormones in Zhuang ethnic pregnant women and explore the role of body mass index (BMI) on thyroid function. A total of 3324 Zhuang ethnic health pregnant women were recruited in this Zhuang population-based retrospective cross-sectional study. The values of thyroid stimulating hormone (TSH), free thyroxine (FT4), and free triiodothyronine (FT3) were determined by automatic chemiluminescence immunoassay analyzer. Multivariate linear regression and binary logistic regression were constructed to evaluate the influence of BMI on the thyroid function. The established reference intervals for the serum thyroid hormones in three trimesters were as follows: TSH, 0.02–3.28, 0.03–3.22, and 0.08-3.71 mIU/L; FT4, 10.57–19.76, 10.05–19.23, and 8.96–17.75 pmol/L; FT3, 3.51–5.64, 3.42–5.42, and 2.93–5.03 pmol/L. These values were markedly lower than those provided by the manufacturers for nonpregnant adults which can potentially result in 6.10% to 19.73% misclassification in Zhuang pregnant women. Moreover, BMI was positively correlated with isolated hypothyroxinemia (OR=1.081, 95% CI=1.007–1.161), while the correlation between the BMI and subclinical hypothyroidism was not statistically significant (OR=0.991, 95% CI=0.917–1.072). This is the first study focusing on the reference ranges of thyroid hormones in Guangxi Zhuang ethnic pregnant women, which will improve the care of them in the diagnosis and treatment. We also found that high BMI was positively associated with the risk of isolated hypothyroxinemia.

Establishment of Early Pregnancy Related Thyroid Hormone Models and Reference Intervals for Pregnant Women in China Based on Real World Data

“…In this study, based on the big clinical data collected from early pregnant women who delivered in the obstetrics and gynecology department of Peking Union Medical College Hospital, we established RIs of thyroid hormones for early pregnant women in China. Moreover, RIs for TSH and FT4 of early pregnancy in previous studies were listed, and our results concerning early pregnancy TSH and FT4 and FT3 RIs are comparable with those of other studies using the same detection platform [27,29]. However, the RIs for TSH and FT4 showed wide variation across studies and analytical systems, with the upper limit of TSH varying between 2.33 μIU/ml and 4.92 μIU/ml and the upper limit of FT4 varying between 1.18 ng/dl and 1.72 ng/dl.…”

“…The TSH and FT4 RIs of early pregnant women as reported previously are shown in ▶ table 4 [25][26][27][28][29][30][31][32][33][34][35][36]. The RIs for TSH and FT4 of early pregnant women showed large differences across studies, and the RIs were different from detection platforms, ethnic and regions.…”

“…Various previous studies have established TSH and FT4 RIs during pregnancy [25][26][27][28][29][30][31][32][33][34][35][36], only a few studies have reported FT3 RIs for pregnant women [27,30,31,33,36]. However, all of these studies were clinical researches and used the direct method to establish RIs.…”

Characterization of Fetal Thyroid Levels at Delivery among Appalachian Infants

“…Upon analysis of thyroid glands from electively terminated fetuses in the second trimester, Filis et al found significant changes in thyroid function, increased fetal thyroid mass and plasma TSH levels, and changes in the expression of genes critical for proper thyroid development based upon maternal BMI [ 30 ]. Another study conducted on Zhuang ethnic pregnant women did not find any statistically significant correlation between BMI and overt hypothyroidism, but a BMI > 25 was associated with a higher risk of overt hypothyroxinemia, defined as having a normal TSH with free T4 levels in the lower 2.5th percentile, based on the reference range for each trimester [ 31 ]. However, our study did not show any association between BMI and thyroid disease.…”

Determinação do intervalo de referência de TSH sérico em mulheres saudáveis no primeiro trimestre gestacional no Distrito Federal segundo recomendações recentes da ATA

“…Em relação a avaliação de correlação entre os valores de TSH e a idade, encontramos uma correlação não relevante estatisticamente (p=0,455; r=0,04). Na literatura recente, observamos uma replicação do resultado encontrado, não sendo identificadas alterações de dosagem sérica de TSH com relevância estatística relacionada à idade das gestantes em um estudo contendo 3324 gestantes (47).…”