Hypothyroidism and Conception: What You Need to Know Before Trying to Get Pregnant

When you have hypothyroidism, a condition where the thyroid gland doesn’t make enough hormones to keep your body running smoothly. Also known as underactive thyroid, it can slow down metabolism, cause fatigue, weight gain, and — critically — make it harder to get pregnant. Many women don’t realize their thyroid is off until they start trying to conceive. That’s because symptoms like irregular periods, low libido, and unexplained weight gain often get blamed on stress or aging. But if your thyroid is underactive, it’s not just about feeling tired — it’s about your body’s ability to ovulate, support a pregnancy, and keep hormones balanced.

Thyroid hormones directly influence the menstrual cycle and egg development. If your TSH levels, the hormone your pituitary gland releases to tell your thyroid to work harder are too high — even slightly — your chances of conceiving drop. Studies show that women with TSH above 2.5 mIU/L before pregnancy have a harder time getting pregnant and face higher risks of miscarriage. That’s why doctors now recommend aiming for TSH between 1.0 and 2.5 mIU/L when trying to conceive, not just staying under 4.0. If you’re on levothyroxine, the most common thyroid hormone replacement used to treat hypothyroidism, your dose often needs to be increased as soon as you start trying to get pregnant — sometimes by 25–50%. Waiting until you’re pregnant to adjust your meds can be too late.

It’s not just about the medication, though. Hypothyroidism often comes with other imbalances — like high prolactin or insulin resistance — that also affect fertility. That’s why simply checking TSH isn’t enough. A full thyroid panel — including free T4, free T3, and thyroid antibodies — gives a clearer picture. If you have Hashimoto’s, the most common cause of hypothyroidism, your immune system is attacking your thyroid, which can make hormone levels unstable. This means you need more frequent monitoring, especially in the first trimester when your baby relies entirely on your thyroid hormones for brain development.

Good news: with the right care, most women with hypothyroidism go on to have healthy pregnancies and babies. The key is planning. Don’t wait for your period to be late to check your thyroid. If you’re thinking about conceiving, get tested. Talk to your doctor about adjusting your levothyroxine dose before you stop using birth control. Track your cycle. Know your numbers. And don’t assume your old dose is still right — your body’s needs change fast when you’re trying to get pregnant.

Below, you’ll find real, practical advice from people who’ve been there — from how to time your blood tests to what to ask your endocrinologist, and how thyroid meds interact with other common supplements. These aren’t theory pieces. They’re the tools you need to take control before you even take that pregnancy test.