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.
Highlights
Thyroid dysfunction is a common endocrine disease during pregnancy, approximately 0.2–0.6% of pregnant women suffer from hypothyroidism, and subclinical hypothyroidism occurs in an additional 3.5–18.0% of pregnant women [1]
The cumulative scientific evidence suggests that gestational thyroid dysfunction can cause adverse pregnancy outcomes, including subclinical hypothyroidism, isolated hypothyroxinemia and thyroid peroxidase antibody (TPO-Ab) positive [9]
Thyroid hormone replacement therapy can effectively reduce the risk of pregnancy loss among women with subclinical hypothyroidism [20]
Summary
Thyroid dysfunction is a common endocrine disease during pregnancy, approximately 0.2–0.6% of pregnant women suffer from hypothyroidism, and subclinical hypothyroidism occurs in an additional 3.5–18.0% of pregnant women [1]. Thyroid hormone deficiency can lead to adverse pregnancy outcomes, including premature delivery, placental abruption, miscarriage and gestational hypertension [4,5]. The guidelines published by ATA in 2017 do not recommend universal thyroid function screening, except for the following patients: thyroid antibody positive, >30 years of age, with a history of adverse pregnancy outcomes, multiple prior pregnancies (≥2), or morbidly obese (BMI ≥40 kg/m2) were recommended to be tested for serum TSH levels. The purpose of the present study was to establish the specific reference value of thyroid hormone in the first trimester of pregnancy in Chinese women, and to explore the effects of HCG, blood lipid status, BMI, age and parity on thyroid hormone status
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