RESUMEN
Introduction: Assessment of thyroid function duringpregnancy is important for assessing maternal and foetalwell being. However, the complex physiological alterationsoccurring during normal pregnancy cause thyroid hormonelevels to change. Hence, the interpretation of the thyroidprofile becomes difficult in pregnancy if normal referenceranges are not defined. Study objective was to determinetrimester specific reference ranges for thyroid hormone innormal pregnancy.Material and methods: Serum sample was collected from194 females in various trimester of normal intrauterine singlepregnancy and total T3, total T4 and TSH was determined.The results obtained were then analysed to determine gestationspecific thyroid hormone levels.Result: The normal ranges of thyroid hormone in first, secondand third trimesters during normal pregnancy in our studywere: total T3 (83.9-196.6, 86.1-217.4, 79.9-186 ng/dl), totalT4 (4.4-11.5, 4.9-12.2, 5.1-13.2 μg/dl) and TSH (0.1-2.7, 0.4-3.3, 0.5-3.8 IU/ml) respectively.Conclusion: The levels of thyroid hormones in pregnancynot only show characteristic changes from non pregnant statebut also vary with each trimester. Hence, trimester specificreference ranges for thyroid hormone need to be defined toensure correct interpretation of these tests.