Key takeaways
Untreated hypothyroidism can be harmful to you and your baby. It can also make it harder for you to get pregnant.
Hypothyroidism in pregnancy can be safely managed with a medication called levothyroxine (Synthroid).
Your healthcare provider may adjust your levothyroxine dose during and after pregnancy.
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If you’ve ever been pregnant, you know that your body goes through many changes during pregnancy. Some changes — like morning sickness — are very obvious to the pregnant person. But other changes may not be so obvious.
In pregnancy, your body adapts to accommodate your growing baby. This includes organs like your thyroid. The thyroid is a butterfly-shaped organ located at the front of your neck. It makes hormones that affect your body in many ways. Thyroid hormones help your muscles, brain, and heart function normally. They also affect how well your stomach works, and make sure your bones remain strong.
In some people, the thyroid doesn’t make enough hormones. This is known as hypothyroidism, and it occurs in about 5% of Americans older than 12 years of age. Hypothyroidism can also occur during pregnancy. Out of every 100 pregnant women, 2 to 3 of them will experience hypothyroidism.
If you have hypothyroidism during pregnancy, you may be wondering what treatment is safe for you and your growing baby. Levothyroxine (Synthroid) is a first-choice option to treat hypothyroidism. Here, we’ll learn how hypothyroidism can affect your pregnancy and why levothyroxine is often recommended.
I’m pregnant with hypothyroidism. Will this affect me or my baby?
Untreated hypothyroidism can be harmful for you and your baby. It can cause serious health complications in pregnancy. These include:
Stillbirth
Delivering your baby before week 37 of pregnancy (preterm labor)
Dangerously high blood pressure (preeclampsia)
Thyroid hormones are also very important for your baby’s brain development, especially in the first trimester. Babies rely on your supply of thyroid hormones for the first three months of pregnancy. At 12 weeks, your baby’s thyroid gland begins to work on its own. But it won’t make enough hormones until 18 to 20 weeks into pregnancy. Your baby still needs your thyroid hormones for the first half of pregnancy.
What does hypothyroidism in pregnancy look like?
Some people won’t experience any symptoms of hypothyroidism. For other people, symptoms of hypothyroidism can look like symptoms of pregnancy itself. Talk to your healthcare provider if you have any symptoms listed below:
Weight gain
Slow heart rate
How often are thyroid hormone levels checked in pregnancy?
If you’re pregnant without hypothyroidism, your thyroid hormone levels may not be checked during pregnancy.
But, this won't be the case if you have hypothyroidism or you’re at high risk of hypothyroidism during pregnancy. In these cases, you can expect your levels to be monitored about every 4 weeks until mid-pregnancy, and at least one time around 30 weeks of pregnancy.
What is levothyroxine and is it safe during pregnancy?
Levothyroxine is a medication used to treat hypothyroidism. It’s a man-made version of a natural thyroid hormone called thyroxine (T4). In hypothyroidism, the body doesn’t make enough T4. When you take levothyroxine, you are raising the amount of T4 so that your body can function properly. Levothyroxine has a long history of safe use in pregnancy. It’s a first-choice medication to treat hypothyroidism in both pregnant and nonpregnant people. It hasn’t been found to raise the risk of miscarriage or birth defects.
I have hypothyroidism. Should I continue levothyroxine while I’m trying to become pregnant?
Yes. Levothyroxine is safe to take while trying to become pregnant. Untreated hypothyroidism is more risky than taking levothyroxine. Low thyroid hormone levels can make it harder to get pregnant and raise the risk of miscarriage. In fact, a study of 200 people trying to become pregnant showed that treating hypothyroidism with levothyroxine significantly raised the chance of becoming pregnant.
If you are trying to become pregnant, let your healthcare provider know. They may want to check your thyroid hormone levels to make sure you have enough thyroid hormone.
Will my dose of levothyroxine change during pregnancy?
Up to 85% of people will need a higher levothyroxine dose during pregnancy.
In a study of pregnant people with uncontrolled hypothyroidism, raising the dose of levothyroxine in the first trimester lowered the risk of pregnancy loss. You’ll probably need to raise your dose within the first 16 weeks of pregnancy. Therefore, it’s important to contact your healthcare provider as soon as you find out you're pregnant. Most pregnant women will need to raise their levothyroxine dose by 20% to 30% in early pregnancy.
Your healthcare provider might tell you to raise your levothyroxine dose before your first prenatal visit. They may tell you to raise your total levothyroxine dose by adding two extra tablets each week. For example, if you’re taking one tablet every day, your healthcare provider might tell you to take an extra tablet 2 days per week.
Will my levothyroxine dose change after I give birth?
After you have your baby, your body won’t need as much thyroid hormone anymore. If you were taking levothyroxine before pregnancy, your dose will likely return back to your pre-pregnancy dose. You’ll likely need to recheck your thyroid hormone levels 6 weeks after birth to make sure you’re taking the right dose.
If you were taking levothyroxine for hypothyroidism that started during pregnancy, you’ll probably be able to stop taking levothyroxine after birth. You’ll likely have your thyroid hormone levels checked 6 weeks after birth to ensure you no longer need the medication.
Can I take levothyroxine while I’m nursing?
High or low thyroid hormone levels can negatively affect your milk supply and make it hard to successfully breastfeed. Since levothyroxine helps normalize your thyroid hormone levels, it helps your body maintain an adequate milk supply.
A small amount of levothyroxine can pass into breast milk. But, it’s not enough to impact the thyroid hormone levels of your baby. If you have hypothyroidism and you’re breastfeeding, you should keep taking levothyroxine. Talk to your healthcare provider if you have any concerns about levothyroxine and breastfeeding.
The bottom line
Uncontrolled hypothyroidism can negatively impact your pregnancy and the health of your baby. To avoid unnecessary risks during pregnancy, take levothyroxine if your healthcare provider recommends it. It’s considered safe to take while trying to become pregnant, while pregnant, or while breastfeeding. If you were taking levothyroxine before becoming pregnant, you may need to raise your dose during pregnancy.
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References
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