Abstract: Hypothyroidism including overt hypothyroidism (OH) and subclinical hypothyroidism (SCH) is the most frequent condition of thyroid dysfunction during pregnancy. The prevalence of SCH during pregnancy ranges from 3% to 5%. In contrast, OH has a prevalence of less than 1% . Currently, pregnancy- specific reference ranges for serum thyrotropin (TSH) and free thyroxin (FT4) are used in the clinical diagnosis of hypothyroidism during pregnancy. More levothyroxine dosage should be taken in pregnant women with OH diagnosed before pregnancy, whereas, pregnant women with newly diagnosed OH should immediately start on levothyroxine (L-T4) therapy to ensure that TSH reaches the target value as soon as possible. As for pregnant women with SCH, there has been a controversy regarding the benefit of L- T4 therapy in preventing adverse pregnancy-related outcome and the suggestion in national and international guidelines. However, recent studies have recommended L-T4 replacement in all SCH women during pregnancy regardless of whether TPO antibodies are positive or negative. This paper reviews the research status of OH and SCH related diagnosis and treatment in pregnancy.

Key words: hypothyroidism, pregnancy complications, thyroxine, thyrotropin, prognosis, review