Reference values and the effect of clinical parameters on thyroid hormone levels during early pregnancy

Abstract

Objective: Thyroid dysfunction is a common endocrine problem during pregnancy; correct diagnosis and appropriate treatments are essential to avoid adverse pregnancy outcomes. Besides, it is vital to identify and quantify the major risk factors for gestational thyroid dysfunction, including thyroid autoimmunity, human chorionic gonadotropin (HCG) concentration, body mass index (BMI) and parity. The study objective was to establish reference ranges during early pregnancy and to explore the relationship between risk factors and thyroid stimulating hormone (TSH), free thyroxine (FT4) and free triiodothyroxine (FT3). Design, patients and measurements: To establish the reference ranges of thyroid hormone during early pregnancy in China and to identify the risk factors for thyroid dysfunction, woman in the first trimester of pregnancy (4–12 weeks gestation) were recruited. After excluding thyroid peroxidase antibody (TPO-Ab) positive and/or thyroglobulin antibody (TG-Ab) positive women, previous thyroid disease, a lack of iodine intake, reference values were calculated by 2.5th to 97.5th percentiles. Results: After exclusion of TPO-Ab and/or TG-Ab positive women, reference values were as follows: TSH, 0.11–3.67 mIU/l; FT3, 3.19–5.91 pmol/l; FT4 10.95–16.79 pmol/l. Higher BMI was associated with lower FT4 concentrations (P=0.005). In multiple regression analysis, TSH was significantly and positively associated with TG (P=0.03). Maternal parity and maternal age may be risk factors for the abnormal thyroidal response to hCG concentrations. Conclusions: Our study defined first trimester-specific reference ranges for serum TSH, FT4, FT3 in a Chinese population, and demonstrated that BMI ≥23kg/m2, maternal parity ≥3 and maternal age ≥30 years may increase the risk of thyroid dysfunction.

Association between gestational blood lipids and TSH levels and pregnancy outcome of patients with subclinical hypothyroidism

“…At the same time, after applying a Pearson analysis, we found that the levels of TC, TG and LDL-C were positively correlated with those of TSH and with the pregnancy outcomes; and, that the TSH levels were positively correlated with the pregnancy outcomes. Lin H et al 27 showed that TSH was significantly and positively associated with TG (P=0.03), which is consistent with this result, but they also found that serial TSH, free thyroxine (FT4) and free triiodothyroxine (FT3) in a Chinese population, and demonstrated that BMI ≥ 23kg/ m2, material degree ≥ three and material age ≥ 30 years may increase the risk of thyroid dysfunction. Our study showed that there is no significant difference in age and gestational week between the two groups, which may be related to the selection of sample size.…”

Maternal Thyroid Hormones as Mediators between Phthalate Exposure and Neonatal Birth Weight: A Cross-Sectional Study from the Zunyi Birth Cohort

“…Thyroid hormones play a crucial role in fetal development, and thyroid hormone levels in pregnant women in Zunyi were low compared to other studies. For example, one study found thyrotropin levels in pregnant women in the first trimester of pregnancy to be 0.11–3.67 mIU/L, FT3 levels to be 3.19–5.91 pmol/L, and FT4 levels to be 10.95–16.79 pmol/L; furthermore, a birth cohort in Beijing found that early pregnancy TSH concentrations were 0.74–5.46u IU/mL, FT3 early pregnancy concentrations of 3.82–5.34 pmol/L, and FT4 early pregnancy concentrations of 12.94–20.58 pmol/L . This phenomenon may be related to environmental and dietary factors in Zunyi, such as endemic iodine deficiency and frequent consumption of pickles and cured meat.…”