If you take levothyroxine and get a positive pregnancy test, contact the clinician who manages your thyroid as soon as you can. Ask about blood tests and whether your dose should change; do not wait for a routine antenatal appointment to raise the question. An elevated TSH during pregnancy can signal that your replacement needs review, but results must be interpreted using appropriate pregnancy and laboratory reference ranges.
Why Levothyroxine Needs Can Rise Early
Pregnancy changes how your body handles thyroid hormone. Levels of a hormone-binding protein rise, and the placenta breaks down thyroid hormones. Together with the increased demands of pregnancy, these changes mean many people with hypothyroidism need more levothyroxine, often starting early. The amount varies, and not everyone needs the same adjustment.
Maternal thyroid hormone is especially important in early pregnancy, before the fetus’s own thyroid is fully functional. This is why an agreed plan matters: you can act promptly without guessing at a dose.
What To Do About Elevated TSH During Pregnancy
Keep taking your prescribed levothyroxine and contact your prescriber, endocrinologist, or pregnancy-care team promptly. If you made a pregnancy plan with your clinician in advance that tells you to increase your dose after a positive test, follow that plan while arranging testing. If you do not have an agreed plan, ask what to do while waiting for results rather than changing your dose on your own.
Some current guidance supports a pre-planned increase of about 20–30% once pregnancy is confirmed; a common approach is adding two extra usual doses per week. That is not a universal instruction for every person. Your starting dose, recent thyroid results, medical history, and local guidance all matter.
A clinician will usually arrange a TSH test and may also check free T4 (FT4), which helps interpret thyroid hormone status alongside TSH. Targets and reference ranges vary: the 2025 Royal College of Obstetricians and Gynaecologists guidance and 2026 American Thyroid Association guidance favor laboratory- and pregnancy-specific ranges where available. For people already treated for hypothyroidism, a reasonable TSH treatment target is 0.5–2.5 mU/L, but your clinician should interpret your result in context. A number from a general online chart cannot set your personal dose.
Expect Follow-Up, Not Just One Test
Thyroid levels may be checked again after a dose change and during pregnancy so the plan can be adjusted. In a retrospective study, Karoline Schack and colleagues reviewed records for 175 people with pre-existing hypothyroidism treated at endocrine departments in Denmark’s North Denmark Region during 2022–2024. About half had a levothyroxine adjustment after testing through week 12, compared with about one in five during weeks 13–24 and one in ten later in pregnancy. This regional study describes care in that group; it does not prescribe a dose or show that every pregnant person needs an increase.
Tell your care team about prenatal vitamins and other supplements. Iron and calcium can interfere with levothyroxine absorption if taken together, so ask how to space them. Also mention biotin, which can affect some thyroid test results; see more about biotin and thyroid testing.
Plan For After Delivery, Too
Your pregnancy dose may not be the right dose after birth. Ask your clinician before delivery what to do postpartum; guidance commonly advises returning to the pre-pregnancy dose and rechecking thyroid function at about six weeks, with individual adjustments as needed. Keep the follow-up appointment even if you feel well.
Regional protocols and laboratory ranges differ, so your local pregnancy-care team should guide testing and dose changes. If you cannot reach your usual clinician, contact your maternity or primary-care service for advice. Seek medical advice if you are unsure about a dose, miss doses, or receive an abnormal result.