When you find out you're pregnant, your body changes in ways you can't always see. One of the most important but often overlooked shifts happens in your thyroid. If you're already taking thyroid medication-usually levothyroxine-your dose likely needs to go up. Not tomorrow. Not next month. Now.
Why Thyroid Medication Changes in Pregnancy
Your thyroid makes hormones that control metabolism, energy, and, most critically for your baby, brain development. Before pregnancy, your body runs on a steady supply. But as soon as you conceive, your baby starts relying on your thyroid hormones for the first 10 to 12 weeks. During that time, your baby can't make its own. If your hormone levels drop even slightly, it can affect how your child’s brain develops. Research shows that untreated or poorly managed hypothyroidism during pregnancy increases the risk of miscarriage by up to 60% and lowers a child’s IQ by 7 to 10 points on average. That’s not a small difference-it’s the gap between average and above-average cognitive performance. The good news? Getting your dose right can prevent almost all of these risks.How Much More Medication Do You Need?
Most women with pre-existing hypothyroidism need 20% to 30% more levothyroxine as soon as they confirm pregnancy. That might sound like a lot, but it’s not guesswork. It’s science. A 2021 NIH study of 280 pregnant women found their average daily dose jumped from 85.7 mcg before pregnancy to 100.0 mcg in the first trimester. That’s a 14.3 mcg increase-roughly one extra tablet every few days. For some, that means adding a 12.5 mcg or 25 mcg pill. For others, it’s doubling their weekly dose on two extra days. Guidelines vary slightly. The American Thyroid Association says to increase your dose by 20-30% immediately after a positive pregnancy test. The American College of Obstetricians and Gynecologists (ACOG) recommends a bigger jump: a 50 mcg increase right away for women already on medication. Why the difference? Because some women need more, and some need less. The key is not to wait. If you’re newly diagnosed during pregnancy, your starting dose depends on your TSH level:- If your TSH is 10 mIU/L or higher: Start at 1.6 mcg per kg of body weight per day.
- If your TSH is under 10 mIU/L: Start at 1.0 mcg per kg per day.
When to Adjust Your Dose
Don’t wait for your first prenatal visit. Don’t wait until you feel tired or cold. Don’t wait for your doctor to bring it up. The moment you know you’re pregnant, increase your dose. Why? Because your baby’s brain is already developing. By week 6, your baby’s thyroid gland is forming, but it still can’t make hormones. Until week 12, it’s all on you. Delaying a dose increase-even by a few weeks-can mean missing a critical window for neurodevelopment. A 2021 study found that women who had their levothyroxine dose adjusted within four weeks of confirmation had 23% fewer preterm births than those who waited longer. That’s not just a statistic. It’s a real outcome: a baby born at 39 weeks instead of 35, a baby who doesn’t spend time in the NICU, a baby who starts life with fewer risks.How to Take Your Medication Correctly
Taking levothyroxine isn’t just about the dose-it’s about how you take it. If you’re not doing it right, your body won’t absorb enough.- Take it on an empty stomach, at least 30 to 60 minutes before eating.
- Avoid calcium, iron, or prenatal vitamins within 4 hours. These minerals bind to the medication and block absorption by up to 50%.
- Don’t switch brands unless your doctor says so. Synthroid, Tirosint, and generic levothyroxine aren’t always interchangeable. Even small differences in fillers can affect how your body uses the drug.
- If you miss a dose, take it as soon as you remember. If it’s almost time for your next dose, skip the missed one. Don’t double up.
Monitoring TSH: The Gold Standard
You can’t guess if your dose is right. You can’t feel it. You need a blood test. The American Thyroid Association recommends checking your TSH:- Within 4 weeks of any dose change
- Every 4 weeks until your levels stabilize
- At least once per trimester after that
- First trimester: ≤2.5 mIU/L
- Second trimester: ≤3.0 mIU/L
- Third trimester: ≤3.0 mIU/L
What If You’re Not on Medication Yet?
Not everyone knows they have hypothyroidism before pregnancy. Some women are diagnosed during prenatal screening. If your TSH is above 4.0 mIU/L, you should start levothyroxine immediately. Even if you have no symptoms. The 2023 ATA guidelines now recommend universal TSH screening for all pregnant women in the first trimester. That’s a big shift. Just five years ago, only high-risk women were tested. Now, because of the evidence linking low thyroid hormone to poor outcomes, screening is becoming standard. If you’re planning pregnancy and have a history of thyroid disease, autoimmune conditions, or a family history of thyroid disorders, get your TSH checked before you conceive. Don’t wait.Real Stories, Real Consequences
One patient on Reddit wrote: “My OB said, ‘Wait and see.’ I waited eight weeks. My TSH was 5.8. I was terrified my baby wouldn’t be okay.” She ended up increasing her dose by 50 mcg, then another 25 mcg. Her baby was born healthy-but she spent months in anxiety. Another woman, on HealthUnlocked, said: “I increased my dose the day I got a positive test. My TSH stayed under 1.5 the whole pregnancy. My daughter is now 18 months and hitting every milestone early.” The difference? Timing. Action. Advocacy.