In normal pregnancy, the maternal thyroid gland undergoes alterations to maintain the necessary levels of thyroid hormones (THs) in each gestational period. However, various factors may reduce TH levels, potentially impacting the onset and development of pregnancy. Such cases of thyroid dysfunction are divided into overt (clinical) hypothyroidism, subclinical hypothyroidism, or isolated hypothyroxinemia, depending on the severity of deficiency. The reported incidence of overt hypothyroidism in pregnancy is 0.3-1.9%, while that of subclinical hypothyroidism is 1.5-5% and that of isolated hypothyroxinemia ranges between 1.3%-25.4%. On a global level, the most common factor for hypothyroidism is iodine deficiency, but in regions where iodine sufficiency is the norm, the most cause is autoimmune thyroiditis or Hashimoto's thyroiditis. Early diagnosis and treatment of low TH levels can play a significant role in lowering the risk of negative outcomes such as recurring miscarriage, gestational hypertension, premature birth, and adverse fetal outcomes. However, there is no agreement on TH reference levels during pregnancy to be used to diagnose thyroid dysfunction, nor is there agreement on universal screening of pregnant women for thyroid function in the first trimester, so specific studies for different populations are needed. In extremely stressful events, as is the case during the COVID-19 pandemic, thyroid function may be altered early in pregnancy, so pregnant women in these situations merit extra monitoring of their thyroid function. As managed hypothyroidism is not a risk factor for more negative outcomes in patients with COVID-19, no extra precautions or measures need to be taken.