From the Guidelines
Levothyroxine is generally considered safe and is actually recommended during pregnancy for women with hypothyroidism. Maintaining proper thyroid hormone levels is crucial during pregnancy as maternal hypothyroidism can lead to complications including miscarriage, preeclampsia, anemia, and impaired fetal brain development 1. Women who are already taking levothyroxine before pregnancy typically need to increase their dosage by about 25-50% during pregnancy, often as early as the first trimester. This increase is necessary because pregnancy increases the body's demand for thyroid hormone.
Key Considerations
- Women should have their thyroid function (TSH levels) checked every 4-6 weeks during the first half of pregnancy and at least once during the second half to ensure proper dosing 1.
- The target TSH level during pregnancy is typically lower than for non-pregnant women, with most guidelines recommending keeping TSH below 2.5 mIU/L in the first trimester and below 3.0 mIU/L in the second and third trimesters.
- Levothyroxine should be taken on an empty stomach, at least 30-60 minutes before breakfast or any other medications, particularly prenatal vitamins containing iron or calcium, which can interfere with absorption.
Monitoring and Adjustments
- The dosage of levothyroxine should be adjusted every four weeks until the TSH level is stable 1.
- Checking the TSH level every trimester is advised to ensure that the thyroid hormone levels are within the recommended range.
- Women with hypothyroidism should be monitored for any signs of complications, such as preterm birth, low birth weight, placental abruption, and fetal death 1.
From the FDA Drug Label
- 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 safety in pregnancy: Levothyroxine is safe to use during pregnancy in women with hypothyroidism. The clinical experience has not reported increased rates of major birth defects, miscarriages, or other adverse maternal or fetal outcomes. However, it is essential to monitor TSH levels and adjust the levothyroxine sodium dosage during pregnancy to maintain a euthyroid state. Untreated hypothyroidism in pregnancy is associated with a higher rate of complications, and levothyroxine sodium should not be discontinued during pregnancy 2.
- Key points:
- Levothyroxine is safe to use during pregnancy.
- Monitor TSH levels and adjust dosage during pregnancy.
- Untreated hypothyroidism in pregnancy is associated with a higher rate of complications.
- Levothyroxine sodium should not be discontinued during pregnancy.
From the Research
Levothyroxine Safety in Pregnancy
- Levothyroxine is a thyroid hormone replacement medication used to treat hypothyroidism (underactive thyroid) in pregnant women.
- The safety of levothyroxine use during pregnancy has been studied extensively, with research indicating that it is safe to use in women with hypothyroidism 3, 4, 5, 6.
- A population-based cohort study found that levothyroxine supplementation in late pregnancy among individuals with hypothyroidism was not associated with prematurity risk 3.
- Another study found that thyroid hormone replacement with levothyroxine reduces the risk of adverse pregnancy outcomes in the setting of overt hypothyroidism 4.
Benefits and Risks of Levothyroxine Use
- Levothyroxine treatment has been shown to have beneficial effects on pregnancy outcomes and offspring development 4, 5.
- However, some studies have found that hypothyroidism in pregnancy is often overlooked or that levothyroxine is not given appropriately to gain tight control of TSH 4, 7.
- Pregnant women using levothyroxine have reported feelings of uneasiness and anxiety due to their hypothyroidism diagnosis, and many have expressed concerns about the treatment burden of levothyroxine use 7.
Management of Hypothyroidism During Pregnancy
- Overt hypothyroidism should always be promptly treated when diagnosed before conception or during pregnancy or lactation 6.
- Most women with pre-existing treated hypothyroidism require an increase in levothyroxine dosing to maintain euthyroidism during gestation 6.
- Close monitoring of serum TSH levels is necessary to avoid overtreatment or undertreatment in LT4-treated pregnant patients 6.
- There is no consensus about whether to initiate levothyroxine in women with mild forms of gestational thyroid hypofunction, but it is reasonable to treat women with subclinical hypothyroidism with levothyroxine, particularly if the TSH level is >10 mIU/L or thyroperoxidase antibodies are present 6.