TSH Interpreter
Compare your TSH with pregnancy reference ranges
* Your laboratory’s pregnancy-specific range takes priority. The third-trimester and TTC comparisons use a general adult range. TSH is interpreted with free T4 and your treatment history; a treatment target is different from a diagnostic limit.
† Dose examples are for discussion if treatment is prescribed. They do not select your dose. Pregnancy and existing treatment can change dose needs. Do not start or change levothyroxine from this result alone.
Normal TSH Levels in Pregnancy Chart
Use your laboratory’s pregnancy-specific range when available. When it is unavailable, the 2026 ATA guideline allows a 0.1–4.0 mIU/L comparison in the first and second trimesters. For the third trimester, this chart uses a general adult fallback of 0.4–4.5 mIU/L.
| Trimester | Reference Range (mIU/L) |
|---|---|
| First Trimester (Weeks 1–12) | 0.1 – 4.0 mIU/L |
| Second Trimester (Weeks 13–26) | 0.1 – 4.0 mIU/L |
| Third Trimester (Weeks 27–40) | 0.4 – 4.5 mIU/L (adult fallback) |
Laboratory ranges differ. The general adult fallback is a comparison, not a universal laboratory range. A lower target used during treatment is a separate consideration.
Levothyroxine Dosage Chart (Hypothyroidism)
Your prescriber considers free T4, TSH, pregnancy stage, current treatment, body weight and medical history when choosing a dose. The examples below describe different treatment settings; they are not interchangeable prescriptions.
| Reference | Setting | Daily dose example |
|---|---|---|
| Low-dose adult example | When a clinician selects a lower starting dose | 25–50 mcg/day |
| Weight-based study example | Nazarpour trial in pregnant women with normal free-thyroxine index and negative TPO antibodies | 1 mcg/kg/day |
| General adult full replacement | When little thyroid function remains and full replacement is appropriate | About 1.6 mcg/kg/day |
| Known Thyroid Disease | Already taking medication | Follow your established pregnancy dose plan; contact your prescriber promptly |
How is "Full Replacement" Calculated?
The general adult full-replacement example uses this daily calculation:
At 70 kg, this gives 112 mcg/day. Pregnancy may require a different dose. For newly diagnosed overt hypothyroidism during pregnancy, current ATA guidance describes a full-replacement calculation of 1.5–1.7 mcg/kg/day with an additional 20–30%; your prescriber decides whether that approach applies.
Frequently Asked Questions
What causes High TSH in pregnancy?
High TSH can indicate that more thyroid hormone is needed. Your clinician interprets it with free T4, your laboratory range, symptoms and current medication.
Is a TSH of 3.5 dangerous?
A TSH of 3.5 falls within the fallback comparison ranges shown here. Your laboratory range, free T4 and existing treatment still matter. A target below 2.5 for someone taking levothyroxine is different from a diagnostic threshold; thyroid antibodies alone do not mean treatment is needed when thyroid function is normal.
Methodology: How this works
1. TSH comparisons
The calculator compares your TSH with the displayed range for your selected stage. The laboratory range on your report takes priority.
- First and second trimesters: 0.1–4.0 mIU/L, the fallback interval in the 2026 ATA guideline when a suitable laboratory interval is unavailable.
- Third trimester and trying to conceive: a general adult comparison of 0.4–4.5 mIU/L. The ATA notes that the nonpregnancy laboratory interval will usually suffice in the third trimester; the exact limits vary by laboratory.
2. Dose examples
Dose examples appear above TSH 2.5. This display threshold does not mean that treatment is needed. TSH alone cannot distinguish overt from subclinical hypothyroidism or choose a dose.
- TSH above 2.5 and up to 10: with weight entered, the calculator shows a 25 mcg/day low-dose example alongside a separate 1 mcg/kg/day calculation used in the Nazarpour trial. These are separate examples, not the endpoints of a recommended personal range. Without weight, it shows the general adult low-dose example of 25–50 mcg/day.
- TSH above 10: the calculator shows a general adult full-replacement example of 1.6 mcg/kg/day. Without weight, 100–150 mcg/day illustrates that formula for adults weighing 62.5–93.75 kg. A high TSH warrants clinical review, but does not by itself establish which dose is appropriate.
Weight in pounds is divided by 2.20462. Changing units converts the entered weight, and calculations retain its unrounded value. Dose examples are rounded to the nearest whole microgram per day; this is not tablet-strength rounding.
Scientific References & Guidelines
- General adult dose references: Jonklaas et al. Guidelines for the Treatment of Hypothyroidism (2014). Sections 4a and 4b describe weight-based full replacement and lower starting-dose examples.
- Weight-based study dose: Nazarpour et al. Effects of Levothyroxine on Pregnant Women With Subclinical Hypothyroidism, Negative for Thyroid Peroxidase Antibodies (2018). The trial used 1 mcg/kg/day; its findings do not establish treatment benefit for TSH 2.5–4.
- Current ATA clinical guidance (2026): American Thyroid Association 2026 Guidelines for Thyroid Disease in Preconception, Pregnancy, and Postpartum. Thyroid, 36(5):481–544.
- American Thyroid Association (ATA): 2017 Guidelines of the American Thyroid Association for the Diagnosis and Management of Thyroid Disease During Pregnancy and the Postpartum. (Earlier pregnancy guidance; updated by the 2026 guideline).
- The Endocrine Society: Management of Thyroid Dysfunction during Pregnancy and Postpartum (2012; retired guideline).
- UpToDate: Hypothyroidism during pregnancy: Clinical manifestations, diagnosis, and treatment.
TSH results and treatment decisions
The 2026 ATA guideline distinguishes an elevated TSH with low free T4 from an elevated TSH with normal free T4. Mild abnormalities may be checked again before treatment. Newly diagnosed mild subclinical hypothyroidism is managed differently in early pregnancy and after the first trimester; TSH above 10 requires prompt clinical review.
When treatment is chosen, the guideline describes low starting-dose examples of 25–75 mcg/day according to clinical circumstances. The dose examples above do not replace that assessment. If you already take levothyroxine, follow your pregnancy treatment plan and contact your prescriber about a new result.