When you're pregnant and have hypothyroidism, a condition where the thyroid doesn't make enough hormone. It's not just about feeling tired—it affects your baby's brain development, especially in the first trimester. This is why levothyroxine, a synthetic form of thyroid hormone used to treat underactive thyroid is one of the most commonly prescribed medications during pregnancy. It’s safe, well-studied, and often needed at higher doses than before pregnancy.
Thyroid hormones don’t just regulate your metabolism—they’re critical for your baby’s nervous system. In early pregnancy, the fetus relies entirely on mom’s thyroid hormone until its own gland kicks in around week 12. If your levels drop too low, even slightly, it can impact your child’s IQ and motor skills. That’s why doctors check your thyroid function test, a blood test measuring TSH and free T4 levels early and often during pregnancy—usually every 4 to 6 weeks. Your dose may need adjusting multiple times, especially in the first half of pregnancy, because your body’s demand for thyroid hormone increases by up to 50%.
Many women worry about taking pills while pregnant, but levothyroxine doesn’t cross the placenta in harmful amounts—it simply replaces what your body can’t make. It’s not the same as thyroid drugs used for weight loss or overactive thyroid. If you’re on levothyroxine and find out you’re pregnant, don’t stop. Talk to your doctor right away. Missing doses or delaying adjustments can be riskier than taking the medication. Also, avoid taking it with prenatal vitamins or calcium supplements—they can block absorption. Take it on an empty stomach, at least 30 to 60 minutes before breakfast.
Not everyone needs medication. Some women develop temporary thyroid changes during pregnancy, like gestational transient thyrotoxicosis, which doesn’t require treatment. But if you have a history of thyroid disease, autoimmune conditions like Hashimoto’s, or even just a family history, testing early is key. Even if you feel fine, low thyroid levels often show no symptoms until it’s too late.
After delivery, your dose often goes back down. But don’t assume you can stop or reduce it on your own. Many women need to stay on levothyroxine long-term, even after pregnancy. And if you plan another pregnancy later, get your levels checked before conceiving—starting off with optimal thyroid function gives your next baby the best start.
Below, you’ll find real-world insights from patients and providers on managing thyroid health through pregnancy, spotting warning signs, understanding test results, and avoiding common mistakes that can put both mom and baby at risk.
Posted By Kieran Beauchamp On 1 Dec 2025 Comments (5)
Thyroid medication needs increase by 20-30% during pregnancy to support fetal brain development. Learn when and how to adjust your levothyroxine dose, what TSH levels to target, and how to monitor effectively for a healthy pregnancy.
READ MORE