Maternal thyroid function test level during the first trimester of pregnancy at a center Yazd, Iran: A cross-sectional study

BACKGROUND: Thyroid dysfunction is associated with negative pregnancy outcomes. There is a lack of reliable information on thyroid hormones in Iranian pregnant women, especially in Yazd. OBJECTIVE: To determine the safe thyroid hormone levels in women of Yazd and also the first trimester-specific reference ranges for serum thyroid-stimulating hormone (TSH), thyroxine (T4), and triiodothyronine (T3). MATERIALS AND METHODS: In this cross-sectional study, the serum of 1,148 women in the first trimester of pregnancy was analyzed. Thyroid function tests (TSH, T4, T3) were measured through radioimmunoassay (RIA) [immunoradiometric (IRMA) for TSH]. The study was conducted in Yazd, from September 2018 to November 2019. Reference intervals were defined as the 5 [Formula: see text] , 50 [Formula: see text] , and 95 [Formula: see text] percentiles. RESULTS: The mean age of the participants was 28.78 ([Formula: see text] 5.86 yr) (range: 15-45 yr). The thyroid hormones reference intervals in the first trimester were TSH (0.2-3.8 mIU/l), T4 (7.45-12.75, [Formula: see text] g/dl), and T3 (100-217 ng/dl). CONCLUSION: The results of the present study determined a local thyroid function measurement in the first trimester of pregnancy at a center of Yazd, Iran. This could facilitate the decision-making of maternal TSH level during the first trimester of pregnancy.