Management of Hypothyroidism and Hypothyroxinemia During Pregnancy

To review the diagnosis and management of hypothyroidism during pregnancy, in the preconception period, and in the postpartum period.

A literature review of English-language papers published between 1982 and 2022, focusing on the most recent literature.

During pregnancy, thyroid function laboratory tests need to be interpreted with regard to gestational age. Overt hypothyroidism, regardless of the thyroid-stimulating hormone (TSH) level, should always be promptly treated when it is diagnosed before conception or during pregnancy or lactation. Most women with pre-existing treated hypothyroidism require an increase in levothyroxine (LT4) dosing to maintain euthyroidism during gestation. LT4-treated pregnant patients need close monitoring of their serum TSH levels to avoid overtreatment or undertreatment. There is no consensus about whether to initiate LT4 in women with mild forms of gestational thyroid hypofunction. However, in light of current evidence, it is reasonable to treat women with subclinical hypothyroidism with LT4, particularly if the TSH level is >10 mIU/L or thyroperoxidase antibodies are present. Women who are not treated need to be followed up to ensure that treatment is initiated promptly if thyroid failure progresses. Additional studies are needed to better understand the effects of the initiation of LT4 in early gestation in women with subclinical hypothyroidism and hypothyroxinemia and determine optimal strategies for thyroid function screening in the preconception period and during pregnancy.

The diagnosis and management of hypothyroidism in the peripregnancy period present specific challenges. While making management decisions, it is essential to weigh the risks and benefits of treatments for not just the mother but also the fetus.