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Drug Info Maternal Matters

Can you take Synthroid during pregnancy?

It’s not only safe, it’s dangerous not to take it if you have a thyroid issue
Valerie Williams headshot
By | Sep. 26, 2024 Medically reviewed by Kimberly Bowman, MD
pregnant person holding belly - Synthroid and pregnancy

Key takeaways

  • Synthroid (levothyroxine) is a prescription medication that treats hypothyroidism and is safe for pregnant women to take.

  • Studies have shown the importance of pregnant women taking levothyroxine to manage hypothyroidism and prevent pregnancy loss.

  • Alternatives to Synthroid include natural desiccated thyroid and other levothyroxine brands such as Eltroxin, Eutroxsig, Levo-T, Levolet, Novothyrox, Thyquidity, and more.

In this article:

Synthroid (a brand name for the generic drug levothyroxine) is a prescription medication used to treat hypothyroidism, a condition in which the body does not produce enough thyroid hormone. Levothyroxine is an artificial thyroid hormone meant to replace what your thyroid gland would make on its own if it were functioning normally. If you took levothyroxine pre-pregnancy, good news—you can continue to take the medication safely starting in the first trimester of pregnancy and beyond.

Can you take Synthroid while pregnant?

Not only is levothyroxine treatment safe during early pregnancy if you already have hypothyroidism, but it’s actually dangerous to not take it. This is because higher levels of thyroid hormone are often needed in pregnant women in order to prevent miscarriage. According to the American Thyroid Association, a 2016 study of women with hypothyroidism who were being treated with Synthroid before becoming pregnant shows there is an increased risk of miscarriage when the thyroid blood test TSH is abnormal, and the dosage of Synthroid is not appropriately increased during pregnancy. Of the women with hypothyroidism and an abnormal TSH level participating in the study who did not increase their medication after becoming pregnant, 36% experienced a miscarriage. The rate of pregnancy loss in the group of women who increased their medication was only 2.4%. There is no increased risk of congenital disorders when a pregnant woman is taking Synthroid.

“It’s safe to take levothyroxine during pregnancy,” confirms Michael A. Reed, MD, a California-based board-certified OB-GYN. “In fact, maintaining proper thyroid function is crucial for both your health and your baby’s development,” he says. A woman’s body needs more thyroid hormone during pregnancy, so it’s very important to continue taking levothyroxine to keep thyroid hormone levels in check. If you are taking levothyroxine and have become pregnant, consult with your healthcare provider, “but this medication is generally well-studied and widely recommended for pregnant women,” says Dr. Reed.

Hypothyroidism diagnosis

A thyroid function test is the first step to determining your thyroid health. A blood test can screen for levels of thyroid-stimulating hormone (TSH). If the TSH level is abnormal, then the next step is a blood test to check for total T3 (triiodothyronine) and free T4 (thyroxine) levels to gauge the health of your thyroid gland. The results will indicate whether you have hyperthyroidism or hypothyroidism. Your TSH and free T4 levels let your healthcare provider know whether you need to be treated with synthetic thyroid hormones like levothyroxine. Pregnant women with an abnormally high TSH level and low free T4 levels have overt hypothyroidism and should be treated with levothyroxine. 

In a pregnant woman who does not have hypothyroidism, there will be an increase in naturally produced thyroid hormone. In women who have hypothyroidism, taking Synthroid or another brand of levothyroxine becomes more important in order to produce enough thyroid hormone to continue a healthy pregnancy. Note that reference ranges for a healthy TSH level change in the first, second, and third trimesters. That’s why it’s important to have levels monitored by a healthcare professional throughout your pregnancy.

Be sure to consult with your OB-GYN and endocrinology specialist with any concerns about levothyroxine treatment and thyroid hormone replacement therapy during pregnancy.

Synthroid dosage

When addressing thyroid dysfunction with medication, it’s important to use the correct dosage. The standard levothyroxine dosage for adults with hypothyroidism is 50-200 mcg once daily, long-term. The maximum Synthroid dosage is 300 mcg once daily. Consult with your healthcare provider and have your thyroid levels tested regularly throughout your pregnancy to determine if your Synthroid dosage needs to be adjusted in order to manage your hypothyroidism.

Subclinical hypothyroidism vs. overt hypothyroidism

In discussing hypothyroidism, it’s important to note that this type of thyroid disease varies in severity. Thyroxine (T4) and triiodothyronine (T3) are the two thyroid hormones released from the thyroid. Together, they are the thyroid hormone that is found in Synthroid. Subclinical hypothyroidism is when thyroid function is a bit low, causing the blood level of thyroxine to be within the reference range, but the blood level of TSH is elevated. This would indicate mild thyroid failure. Subclinical hypothyroidism may not always require medication, and sometimes, treating the condition with levothyroxine may cause more harm than good due to medication overtreatment.

Overt hypothyroidism presents with below-normal levels of thyroxine, which may cause symptoms such as weight gain, fatigue, cold intolerance, dry skin, and an increased risk of cardiac issues. Overt hypothyroidism, however, typically requires daily thyroid medication to manage.

What are the risks of taking Synthroid while pregnant?

Managing thyroid disorders during pregnancy is very important for the health of the pregnant woman and the fetus. “The risks associated with taking Synthroid during pregnancy are generally minimal,” explains Dr. Reed. “The biggest ‘risk’ would be not taking it if you need it,” he says. “Synthroid is well-tolerated, and most side effects, like slight changes in appetite or heart rate, are rare,” he explains. “The benefits of Synthroid far outweigh the risks when it comes to ensuring your thyroid levels are where they need to be for a healthy pregnancy.”

While side effects of levothyroxine are rare, overuse of the medication “can lead to negative impacts on the body’s homeostasis,” says Kecia Gaither, MD, a double board-certified OB-GYN and maternal-fetal medicine specialist and director of Perinatal Services/Maternal Fetal Medicine at NYC Health + Hospitals/Lincoln in the Bronx. Overuse of thyroid medication means getting more thyroid hormone than your body actually needs. The dosage is often weight-based, and of course, weight changes throughout pregnancy. For this reason, it’s very important to have your thyroid hormone levels monitored for the duration of your pregnancy.

The side effects of overuse, according to Dr. Gaither, include an increased risk of the following:

  • Chest pain
  • Tachycardia (rapid heartbeat)
  • Vomiting/diarrhea
  • Excessive sweating
  • Nervousness
  • Irritability
  • Muscle spasms
  • Heat intolerance
  • Weight loss
  • Decreases in bone density

While thyroid hormones do cross the placenta, levothyroxine is the synthetic version of naturally produced thyroid hormone and should not be dangerous to the fetus, says Dr. Gaither.

Women with hypothyroidism should continue to take levothyroxine postpartum as well. “It’s safe to breastfeed while using levothyroxine,” says Dr. Gaither. “Just be sure that there is constant oversight by your endocrinologist and TSH levels have normalized while on the medication.”

“Your thyroid hormone levels impact your overall health, and keeping them stable is important for both you and your baby,” agrees Dr. Reed. “Synthroid passes into breast milk in very small amounts, but it’s not considered harmful to your baby.” Consult with your healthcare provider if you have concerns about the safety of taking levothyroxine during pregnancy or the postpartum period while managing your hypothyroidism.

What are the risks of not treating hypothyroidism while pregnant?

All thyroid problems and their possible treatments should be thoroughly discussed with a healthcare professional at the start of your pregnancy to determine the risks and benefits of any treatment. While all medications have the potential for side effects, it’s important to note that with conditions like maternal hypothyroidism, there is a higher risk of not taking medication to manage the disease. Below are possible pregnancy complications of not treating hypothyroidism, according to the guidelines of the American Thyroid Association:

  • Developing preeclampsia (sudden high blood pressure that releases protein in the urine)
  • Gestational hypertension (high blood pressure)
  • Maternal anemia
  • Muscle pain and weakness
  • Congestive heart failure
  • Placental abnormalities
  • Postpartum hemorrhage
  • Low birth weight
  • Preterm birth/preterm delivery
  • Miscarriage
  • Stillbirth

For the best pregnancy outcome, it is critical to speak to your healthcare provider early in the first trimester about continuing to treat your thyroid disease and monitor TSH levels to be sure the dosage of levothyroxine is adequate. “Your thyroid hormones play a vital role in your fetus’s growth, especially in the early stages, so managing your thyroid condition is crucial for a healthy pregnancy and a healthy baby,” cautions Dr. Reed.

What can I take instead of Synthroid during pregnancy?

“Synthroid, or levothyroxine, is the go-to treatment for hypothyroidism, but there are other options if necessary,” says Dr. Reed. “Some people use natural desiccated thyroid (like Armour Thyroid), which contains both T3 and T4 hormones.” However, he notes that most OB-GYNs prefer Synthroid during pregnancy “because it offers a stable, consistent dose of T4, which your body then converts to T3 as needed.”

“Alternatives to levothyroxine can work, but it’s essential to discuss them with your doctor to ensure they’re safe for you and your baby,” says Dr. Reed.

Other brands of levothyroxine include:

Natural remedies for thyroid control during pregnancy

Thyroid disease management is crucial for pregnant women, and any proposed changes to the treatment of pre-existing hypothyroidism should be thoroughly discussed with your healthcare provider before stopping a medication that manages your TSH levels. If you are interested in trying natural remedies to help keep thyroid function healthy during pregnancy, there are some available:

  • Selenium: The body needs selenium for a number of reasons, including improved thyroid function. While selenium supplements are available, you can get selenium in your diet by eating seafood, meat, poultry, eggs, dairy products, breads, cereals, and other grain products.
  • Herbal remedies: Nigella sativa L., ashwagandha, and Mentha x Piperita L. may all improve symptoms of hypothyroidism. However, the safety of using most herbal remedies in pregnancy has not been established. Check with your healthcare provider before starting any new supplements during pregnancy.
  • Dietary changes: Avoid foods high in soy, as they may interfere with the absorption of thyroid medications. Try to consume a diet high in fruits, vegetables, and whole grains. Any proteins, such as poultry or fish, should be lean.

Again, normal thyroid function is especially important during pregnancy, so do not stop taking your thyroid medication in favor of natural remedies without discussing it with your healthcare providers. Together with your OB-GYN and endocrine specialist, you can be sure your thyroid disease is treated so you can have a healthy and happy pregnancy.

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