Maintenance of thyroid function during pregnancy is critical for both maternal and fetal health and development; therefore, knowledge regarding the relationship between thyroid hormones and pregnancy is essential. The American Thyroid Association task force has developed clinical guidelines on the diagnosis and treatment of thyroid disease during pregnancy. Gestational thyroid diseases are divided into two classifications, hypothyroidism and hyperthyroidism, which are further divided into more specific classifications based on clinical presentation. Differentiation, diagnosis, and monitoring of thyroid diseases throughout pregnancy require assessing symptoms, as well as obtaining levels of thyroid-stimulating hormone (TSH) and free thyroxine (FT4) concentration by a simple serum test. Treatment goals are based on trimester-specific normal ranges of these hormone levels. Uncontrolled hypothyroidism and hyperthyroidism during pregnancy can lead to adverse pregnancy complications and have negative effects on fetal development. However, debate still exists as to the benefit of thyroid hormone level screening in all pregnant patients versus only those with higher risk.