Introduction: Hypothyroidism during pregnancy can lead to multiple adverse effects on both mother and child. Children born to untreated or undertreated mothers suffer profound effects on intellectual development. Subclinical hypothyroidism (SCH) is another important subset and knowledge of SCH in pregnancy is evolving. There are only a few studies on this aspect from South Asia. Objectives: 1. To estimate the prevalence and patterns of hypothyroidism in pregnant women 2. To assess SCH and its association with clinic-demographic variables such as age, residence, consanguinity, duration of pregnancy, parity, diet, obesity and autoimmunity. Methodology: This was a cross-sectional study conducted at JSS Hospital, a Tertiary Care Teaching Hospital, Mysore between Jan 2017 to June 2019. 500 women in the first trimester of pregnancy were included. Detailed history and clinical examination were recorded and blood samples were analysed for Hb, T3, T4, TSH and anti-TPO antibodies. Data were analyzed concerning associations. Results: Out of 500, the results of 9 subjects were ineligible for analysis because of preanalytical lab error. The prevalence of Hypothyroidism in first trimester pregnant women was 156/491 (31.77%), Of this9(5.76%) had overt hypothyroidism and 147(94.23%) had subclinical hypothyroidism, and7 (1.42%) had hyperthyroidism. Clinicodemographic variables as mentioned above were not significantly associated with SCH except the presence of anti-TPO antibody(p__ampersandsignlt;0.001). Conclusions: The prevalence rate of hypothyroidism was very high in our setting compared to that seen in other published reports. Positive Anti-TPO antibody was significantly associated with SCH. There is a need for routine screening of hypothyroidism in the first trimester itself.