Thyroid hormones reference ranges during each trimester of normal pregnancy subjects in Andhra Pradesh, South India

Background: The Thyroid hormones normal levels are very much essential for fetal neural development and good pregnancy outcome. Thyroid insufficiency during pregnancy may be associated with adverse obstetric outcome and fetal neurodevelopmental deficits. The main objective of the study is to estimate and establish the reference ranges of thyroid hormones as it varies from place to place and inter dependent on the iodine levels as the American Thyroid Association strongly recommends to refer to population defined trimester-specific reference ranges.Methods: A longitudinal study was conducted at obstetric clinic, Kakinada city, Andhra Pradesh over a period of 18 months. The total number of normal pregnancy subjects included in this study was 126. Thyroid hormones estimation was done by Competitive electrochemiluminescence (T3 and T4) and Sandwich electrochemiluminescence (TSH) at Thyorocare Laboratory. Only 47 subjects were having all three trimester thyroid hormone levels estimated during each trimester and were followed up to full term. The 2.5th and 97.5th percentiles were calculated as the reference intervals for thyroid hormone levels during each trimester.Results: The thyroid hormone levels during first, second and third trimesters median with reference intervals - Total Triiodothyronine (T3) : 163(100.2-230), 168(121-219.2), 168(110.2-222.6) ng/dl ,Total Thyroxine (T4) : 8.4(4.05-16.64) , 10.2(4.09-18.7), 11.2(3.8-16.7) μg/dl and Thyroid Stimulating Hormone (TSH ):2.52(1.6-7.9) 3.01(1.28-7.6) 3(1.5-8.4) μIU/mlConclusions: The trimester-specific reference intervals and median for thyroid hormones during normal pregnancy have been established for pregnant South Indian women in Andhra Pradesh by full term follow-up during pregnancy using 2.5th and 97.5th percentiles and median.