Levothyroxine dose before trying to conceive

What does the evidence say about levothyroxine dose before trying to conceive while trying to conceive?

1. Thyroid conditions, including untreated or undertreated hypothyroidism, can come with ovulatory dysfunction, irregular periods, and infertility, which is part of why optimizing thyroid function is a piece of preconception planning. 1
2. A commonly cited target for women planning pregnancy is a TSH level at or below 2.5 mIU/L before conception is attempted. 2
3. Once pregnant, guidelines call for maintaining TSH under 2.5 mIU/L in the first trimester and under 3.0 mIU/L in the second and third, and somewhere between half and the large majority of women with existing hypothyroidism need a higher levothyroxine dose, typically around 30% above their pre-pregnancy amount. 1
4. Current guidance recommends increasing the levothyroxine dose immediately when a pregnancy is discovered rather than waiting on lab results, in practice often done by adding two extra tablets a week, and dose needs rise by roughly half again during the first trimester before leveling off for the rest of pregnancy. 3
5. Once pregnancy is confirmed, thyroid levels are generally rechecked every 4 to 6 weeks through the first half of pregnancy and at least once after 30 weeks so the dose can be adjusted as needed. 4

What to know about levothyroxine dose before trying to conceive while trying to conceive

• Before you start trying, work with your provider toward a TSH at or below 2.5 mIU/L. Thyroid conditions, including undertreated hypothyroidism, have been linked to ovulatory dysfunction and irregular cycles, so getting levels settled first can matter for how easily you conceive, not only for the pregnancy that follows.
• The moment you get a positive test, plan on increasing your dose rather than waiting for a lab appointment. Current guidance calls for an immediate bump, often implemented in practice as adding two extra tablets of your usual dose per week, since levothyroxine needs typically climb early in pregnancy.
• Expect your dose need to keep rising through the rest of the first trimester, roughly half again higher than your pre-pregnancy dose, before it levels off. Levels are typically rechecked every 4 to 6 weeks through the first half of pregnancy and at least once after 30 weeks so your provider can fine-tune the dose.