Hypothyroidism is a disorder of the endocrine system in which the thyroid gland does not produce enough thyroid hormones. During pregnancy, there is a change in thyroid function and inadequate adaptation to these changes result in thyroid dysfunction. In pregnancy, thyroid gland may enlarge to a greater extent in iodine poor countries. A cross sectional study was conducted on 150 pregnant women to find out the prevalence of hypothyroidism in different trimesters of pregnancy. The prevalence of hypothyroidism among pregnant women was found to be 14.7%. The result showed that there is a high prevalence of subclinical hypothyroidism in first trimester of pregnancy in Lucknow area.