Adequate thyroid hormone in pregnancy is critical for healthy fetal development. Thyroid disease is the most common endocrine problem in women of reproductive age. Hypothyroidism is estimated to occur in 4% of pregnancies and hyperthyroidism in 2.4% of pregnancies, majority of cases being subclinical thyroid dysfunction. Although adverse effects of overt thyroid dysfunction in pregnancy on obstetric and offspring outcomes are well established, impact and need for treatment of subclinical thyroid dysfunction are more debated. Studies suggest increasing evidence of subclinical hypothyroidism leading to adverse pregnancy and offspring neurodevelopmental outcomes. However, no clear benefit of levothyroxine treatment of subclinical hypothyroidism in pregnancy is established in currently available clinical trials. Treatment of subclinical hypothyroidism in pregnancy needs to be individualized based on the degree and persistence of dysfunction and timing of diagnosis. On the other hand, there is no clear evidence of adverse impact of subclinical hyperthyroidism on pregnancy or offspring outcomes. Treatment of subclinical hyperthyroidism in pregnancy is not recommended. This review summarizes current evidence in assessment of thyroid function in pregnancy, evaluation and treatment considerations of subclinical thyroid dysfunction in pregnancy, and screening recommendation for thyroid dysfunction in pregnancy.