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Levothyroxine is used to treat hypothyroidism (underactive thyroid gland), a condition in which the body’s functions slow down. Hypothyroidism can increase the risk of pregnancy complications. Levothyroxine is considered safe to be used during pregnancy. Euthyroid pregnant women with normal thyroid function who are treated with levothyroxine have a lower risk of pregnancy complications. 

Pregnant women should get regular blood tests while taking thyroid hormone treatment to ensure the medication and the prescribed dosage are working properly. If levothyroxine treatment has been started before pregnancy is confirmed, the dose needs to be adjusted during pregnancy. 

Please continue reading to find out how thyroid hormone levels affect the developing baby and pregnancy outcomes. We will also talk about adjustments in levothyroxine doses during pregnancy.

Diagnosis of thyroid problems in pregnancy

Thyroid problems can be hard to diagnose during pregnancy because pregnancy hormones such as human chorionic gonadotropin (hCG) and estrogen can lead to an increase in thyroid hormone levels. In addition, many of the symptoms of thyroid disorders and pregnancy are similar and can be challenging to differentiate. However, some symptoms of thyroid problems are easier to identify during pregnancy and may prompt your healthcare provider to test you for thyroid disease.

Fetal thyroid gland in pregnancy

During the first 3 months of pregnancy, the baby obtains thyroid hormones from the mother through the placenta. The fetal thyroid gland starts functioning at around 12 weeks gestation but does not produce enough thyroid hormones until 18-20 weeks (second and third trimesters). Therefore, levothyroxine replacement in hypothyroid pregnant women is vital to ensure the baby gets enough thyroid hormones, especially in early pregnancy.

Can I get pregnant while taking levothyroxine?

Yes, you can get pregnant while taking levothyroxine. This medication helps to treat hypothyroidism. Untreated hypothyroidism can lead to fertility problems and make it harder for you to conceive. Correcting thyroid dysfunction with levothyroxine therapy will bring your thyroid hormone levels back to normal. This will not only help you get pregnant but also lower your risk of pregnancy complications. The good news is that levothyroxine is considered to be safe to use during pregnancy.

If you have had hypothyroidism diagnosed and are planning to get pregnant, tell your doctor. They may adjust the dose of levothyroxine tablets to keep your TSH level in the lower half of the reference range to reduce your risk of miscarriage. Check out: “How Long Does It Take for Levothyroxine to Work?”

Note: Both men and women with hypothyroidism can experience fertility problems. 

Is it safe to take levothyroxine while pregnant?

It is safe to take levothyroxine while pregnant. Evidence-based guidelines recommend adequate replacement of thyroid hormone with levothyroxine during pregnancy (and even before conception) to reduce adverse outcomes. 

This thyroid medication is the mainstay of treatment for hypothyroidism in pregnant women. Treatment for hypothyroidism during pregnancy is especially important in early pregnancy until your baby can make their own thyroid hormone. Levothyroxine is safe for your baby during pregnancy. It is also safe for you to take levothyroxine if you are nursing an infant with breast milk.

How do I adjust my thyroid medication during pregnancy?

Your healthcare provider will adjust your thyroid medication during pregnancy by checking thyroid function tests every 4-6 weeks during the first and second trimesters and at least once in the third trimester.

How much to increase levothyroxine in pregnancy?

If you had a diagnosis of hypothyroidism before you became pregnant and are on levothyroxine treatment, you will likely need to increase your dose during pregnancy, especially during the first 20 weeks. Your doctor may recommend taking an extra dose of your thyroid medication on two days every week or increasing your dose by 25 mcg to 50 mcg daily as soon as pregnancy is confirmed.

What are levothyroxine doses after childbirth?

Hypothyroid women usually go back to their pre-pregnancy levothyroxine doses after childbirth. Your doctor will order blood tests to measure thyroid hormone levels a few weeks after you give birth. 

Can I take Armour Thyroid instead of Synthroid during pregnancy?

Taking Armour Thyroid instead of levothyroxine or Synthroid is not recommended during pregnancy. Synthroid is a brand name product for levothyroxine (T4), which is the gold standard for hypothyroidism treatment. 

Armour Thyroid is a form of natural desiccated thyroid extract (DTE) obtained from animal thyroid glands. It contains both T3 and T4. 

Also, while Synthroid is the brand name of the generic drug levothyroxine, these two drug products (and other brand names) are not interchangeable. Switching between different levothyroxine brands may cause abnormal thyroid function tests. Switching to a different levothyroxine product is only acceptable under the supervision of a healthcare professional. 

However, in early pregnancy, T3 does not enter the baby’s brain like T4. Instead, T4 is converted to T3. Therefore, even though Armour Thyroid contains T3, it is not useful for the baby’s brain development. The amount of thyroid hormones in Armour Thyroid can vary and may include too much T3 and not enough T4. Therefore, doctors recommend taking levothyroxine to treat hypothyroidism during pregnancy. This medication is lab-made and provides a precise dose of T4 hormone to you and your baby while you’re pregnant.

What are the risks of untreated hypothyroidism during pregnancy?

Normal thyroid function in the mother is essential for an uncomplicated pregnancy. Untreated hypothyroidism, especially in early pregnancy, can lead to adverse fetal outcomes. Thyroid hormones are vital for fetal neurocognitive development (brain development). 

Untreated maternal hypothyroidism during pregnancy can lead to adverse pregnancy outcomes, including an increased risk of: 

• Gestational hypertension (high blood pressure in pregnancy)

• Preeclampsia (a dangerous rise in blood pressure)

• Gestational diabetes (elevated blood sugar levels)

• Congestive heart failure (rare)

• Anemia

• Pregnancy loss (miscarriage)

• Intrauterine growth restriction

• Preterm birth

• Low birth weight

• Stillbirth

• Postpartum hemorrhage (excessive bleeding in the postpartum period) 

Untreated women with low thyroid hormones, especially in the first trimester, also put their baby at a higher risk of adverse neonatal outcomes, such as problems with growth and development and low IQ.

Note: Treatment of overt hypothyroidism during pregnancy is recommended. However, if you have subclinical hypothyroidism (mildly elevated serum TSH levels and no symptoms), you may not need levothyroxine treatment during pregnancy. 

Understanding the thyroid gland

Thyroid gland

The thyroid gland is a small butterfly-shaped gland located in the anterior part of the neck that makes mainly two thyroid hormones, triiodothyronine (T3) and thyroxine (T4). Sometimes, the thyroid gland makes too much or too little thyroid hormones. These conditions are called hyperthyroidism (overactive thyroid gland or too much thyroid hormone) and hypothyroidism (underactive thyroid gland or too little thyroid hormone).

Normal thyroid function

Normal thyroid function is important for the regulation of many processes in the body, including metabolism, body temperature, heart rate, digestion, muscle contraction, skin and bone function, brain development, and fertility.

Thyroid-stimulating hormone

Thyroid-stimulating hormone (TSH) is a hormone made by the pituitary gland in the brain. TSH tells the thyroid gland to make thyroid hormones based on the levels sensed by the pituitary gland in the blood. If thyroid hormone levels are low, TSH secretion by the pituitary increases, which tells the thyroid to make more thyroid hormones. Therefore, serum TSH levels are high in people with untreated hypothyroidism.

Health care providers can measure TSH with a blood test to detect hyperthyroidism, hypothyroidism, and other thyroid disorders. Other thyroid function tests include tests to measure T3 and T4 (thyroid hormone levels in the blood) and thyroid antibody tests (thyroid peroxidase antibodies, thyroglobulin antibodies, and thyrotropin receptor antibodies) to diagnose autoimmune thyroid disease.

Decreasing the risk of adverse maternal and neonatal outcomes

Taking your levothyroxine as prescribed to treat hypothyroidism during pregnancy can protect both you and your baby from adverse outcomes. It is also important to keep all your medical and lab appointments so that your health care providers can adjust your levothyroxine dose during pregnancy. This will ensure your baby has an adequate supply of thyroid hormones for growth and development.