Trimester-specific reference intervals for thyroid function parameters in Indian pregnant women during final phase of transition to iodine sufficiency

摘要

Background: Interpretation of thyroid function tests during pregnancy depends on gestational age, method, and population-specific reference intervals. Therefore, there is a worldwide trend to establish trimester-specific levels for different populations. The aim of this study was to establish a trimester-specific reference range for thyroid function parameters during pregnancy in Indian women.Materials and Methods: Thyroid function tests (TSH, FT4, TT4, TT3) of 80, 76, and 73 women at 1supst/sup, 2supnd/sup, and 3suprd/sup trimester, respectively, and 168 nonpregnant women were analyzed after exclusion of low UIC( μg/L) and anti-TPO positivity(35 IU/ml). Urinary iodine excretion (UIC) was assessed in all. The 2.5supth/sup and 97.5supth/sup percentile values were used to determine the reference ranges for thyrotropin (TSH), free thyroxine (FT4), total thyroxine (TT4), and total triiodothyronine (TT3) for each trimester of pregnancy. Results: The reference range for TSH for first trimester was 0.19–4.34 μIU/ml, for second trimester 0.46–4.57 μIU/ml, and for third trimester 0.61–4.62 μIU/ml. The reference range during three trimesters for FT4 (ng/dl) was 0.88–1.32, 0.89–1.60, and 0.87–1.54, for total T4 (μg/dl) was 5.9–12.9, 7.4–15.2, and 7.9–14.9. In nonpregnant women, FT4 was 0.83–1.34, total T4 was 5.3–11.8, and TSH was 0.79–4.29. The mean UIC in nonpregnant women was 176 ± 15.7 μg/L suggesting iodine-sufficiency in the cohort. Conclusion: The trimester-specific TSH range in pregnant women in this study is not significantly different from nonpregnant reference range in the final phase of transition to iodine sufficiency in India.