Is levothyroxine (T4) safe during pregnancy?

From the Guidelines

Levothyroxine is safe to use during pregnancy, and its benefits in managing hypothyroidism outweigh the risks, as it helps prevent complications for both mother and baby. The use of levothyroxine in pregnant women is supported by guidelines that recommend treating women with elevated serum TSH to restore normal thyroid function and prevent potential complications such as fetal wastage or neuropsychological problems in the offspring 1. It is essential to monitor serum TSH concentrations every 6 to 8 weeks during pregnancy and adjust the levothyroxine dose as needed, as the requirement for levothyroxine often increases during pregnancy.

Some key points to consider when using levothyroxine during pregnancy include:

• Regular monitoring of thyroid function through blood tests to ensure proper dosing
• Adjusting the levothyroxine dose as needed, especially during the first trimester
• Informing the healthcare provider immediately if pregnancy occurs while taking levothyroxine
• Maintaining normal thyroid levels with levothyroxine to ensure proper fetal development

According to the guidelines, the risks of appropriately managed levothyroxine therapy in pregnancy are minimal 1. Another study also supports the use of levothyroxine in pregnant women, recommending that hypothyroidism be treated with levothyroxine to return the TSH level to normal, with dosage adjustments every four weeks until the TSH level is stable 1. However, the most recent and highest-quality study 1 provides the strongest evidence for the safety and efficacy of levothyroxine during pregnancy.

From the FDA Drug Label

1. 1 Pregnancy Risk Summary The clinical experience, including data from postmarketing studies, in pregnant women treated with oral levothyroxine to maintain euthyroid state have not reported increased rates of major birth defects, miscarriages, or other adverse maternal or fetal outcomes. There are risks to the mother and fetus associated with untreated hypothyroidism in pregnancy Since TSH levels may increase during pregnancy, TSH should be monitored and levothyroxine sodium dosage adjusted during pregnancy Levothyroxine sodium should not be discontinued during pregnancy and hypothyroidism diagnosed during pregnancy should be promptly treated

Levothyroxine use during pregnancy is considered relatively safe when used to maintain a euthyroid state.

• The drug label states that there are no increased rates of major birth defects, miscarriages, or other adverse maternal or fetal outcomes associated with levothyroxine use during pregnancy.
• However, untreated hypothyroidism poses risks to both the mother and the fetus.
• It is recommended to monitor TSH levels and adjust the levothyroxine dosage as needed during pregnancy.
• Levothyroxine should not be discontinued during pregnancy, and hypothyroidism diagnosed during pregnancy should be promptly treated 2.

From the Research

Safety of Levothyroxine During Pregnancy

• The use of levothyroxine in obstetric practices requires a correct diagnosis and consideration of specific recommendations for each thyroid dysfunction entity 3.
• Levothyroxine therapy is strongly recommended in all cases of overt hypothyroidism and in cases of subclinical hypothyroidism associated with positive thyroid autoimmunity 3.
• The effectiveness and safety of levothyroxine treatment in preventing adverse perinatal events in pregnant women with clinical hypothyroidism is supported by all current guidelines 3.

Benefits and Risks of Levothyroxine Treatment

• Levothyroxine treatment reduces the risk of adverse pregnancy outcomes in the setting of overt hypothyroidism 4.
• Meta-analyses suggest that subclinical hypothyroidism reduces the chance of a successful pregnancy outcome, and guidelines support intervention for some patients with subclinical hypothyroidism 4.
• However, some patients may experience concerns and anxiety related to levothyroxine treatment, highlighting the need for effective communication and tailored counseling 5.

Therapeutic Regimen and Dosing

• Recent guidelines recommend thyrotropin (TSH) target levels of ≤2.5 mIU/L for the first trimester and ≤3 mIU/L for the subsequent trimesters 6.
• The appropriate levothyroxine dose for women with subclinical hypothyroidism is lower than for those with overt hypothyroidism, and the dose should be adjusted based on basal TSH levels 6.
• Initiating treatment with the recommended levothyroxine doses can help patients promptly attain the euthyroid state and avoid additional increments and potential obstetric risks 6.