Objectives: The present study was conducted to assess the maternal thyroid functions (triiodothyronine [T3], thyroxine [T4], and thyroid stimulating hormone [TSH]) during the first trimester of pregnancy and also to determine the proportion of thyroid dysfunction in these subjects.

Materials and Methods: 80 apparently normal the first trimes- ter pregnant women were randomly selected and were aged between 18 and 35 years from the outpatient department of Obstetrics and Gynaecology, Vijayanagara Institute of Medical Sciences, Ballari. The T3, T4, and TSH levels were estimated using chemiluminescent immunoassay method.

Results: The mean total T3 and T4 levels were significantly increased during 10-12 weeks of gestation as compared to 6-9 weeks with P value of 0.03 and 0.02, respectively. Based on American Thyroid Association guidelines for TSH values during the first trimester of pregnancy, the proportion of thyroid dysfunction was found to be high, of which 16.3% were in hypothyroid range, and 2.5% were in hyperthyroid range. Conclusion: A high proportion of thyroid dysfunctions (16.3% in hypothyroid range and 2.5% in hyperthyroid range) was observed during the first trimester of pregnancy, and hence a routine antenatal screening is suggested, to diagnose the thyroid dysfunction at the earliest.