TSH in Pregnancy — What It Means
Informational only. Antenatal results should always be discussed with your obstetrician, who interprets them for your specific pregnancy.
TSH (Thyroid-Stimulating Hormone) is a hormone from the pituitary gland in your brain. It controls how much thyroid hormone your thyroid gland makes. Thyroid hormones matter for your baby's brain growth. In the first trimester your baby has no thyroid yet. So your own thyroid is watched closely.
First trimester · Second trimester · Third trimester
Last reviewed: 2026-08-16
When is it done?
You ideally have this at your first antenatal visit, before 10 weeks. It is repeated in the second trimester if the result is off. It is also repeated if you have known thyroid disease.
Why is it done in pregnancy?
Thyroid hormones matter for your baby's brain growth. In the first trimester your baby has no thyroid yet. So your own thyroid is watched closely.
Trimester-specific ranges
Trimester 1
Approximately 0.1–2.5 mIU/L (population- and laboratory-specific; verify with your lab)
Sources: [American Thyroid Association (ATA), 2017]
Trimester 2
Approximately 0.2–3.0 mIU/L (population- and laboratory-specific; verify with your lab)
Sources: [American Thyroid Association (ATA), 2017]
Trimester 3
Approximately 0.3–3.0 mIU/L (population- and laboratory-specific; verify with your lab)
Sources: [American Thyroid Association (ATA), 2017]
What to discuss with your obstetrician
Ask your obstetrician if your TSH result fits your lab's trimester range. Also ask if thyroid antibody testing or more monitoring is right for you.
Questions to ask your obstetrician
About this result
- What does my TSH result mean for me and my baby at this stage of pregnancy?
- Is my TSH being read against a pregnancy-specific range?
What to do next
- Based on my TSH, is there anything you would suggest I do or change during this pregnancy?
About retesting
- Will my TSH be checked again later in the pregnancy, and if so, when?
The bigger picture
- How does my TSH fit with the rest of my antenatal checks?
Frequently asked questions
- Why does the TSH range change in each trimester?
- Pregnancy hormones, especially hCG, nudge the thyroid. This makes TSH drop in the first trimester. The ranges then shift across the trimesters. This reflects normal changes in your body.
- Can I use a single general TSH normal range during pregnancy?
- No. The ATA advises against using one general range in pregnancy. It says each lab should set its own ranges for each trimester. These should come from its local pregnant women. A single global number is not right.
- What if my TSH is low in the first trimester?
- A slightly low TSH in the first trimester can be normal. It is driven by hCG. Whether it needs action depends on your free T4, symptoms, and your obstetrician's view. Do not change any thyroid medicine without asking your obstetrician.
- Does untreated hypothyroidism affect my baby?
- Well-managed thyroid levels in pregnancy support your baby's brain growth. Your obstetrician will advise on the right monitoring and care for your result.
- Do I need to test TSH if I am already on thyroid medication?
- Yes. Thyroid needs often rise during pregnancy. So TSH is usually checked more often if you already take thyroid hormone tablets. This makes sure the dose stays right.
Sources
- American Thyroid Association (ATA) (2017) — 2017 Guidelines for the Diagnosis and Management of Thyroid Disease During Pregnancy and the Postpartum, Thyroid 27(3):315–389
- FOGSI (2019) — FOGSI Position Statement on Thyroid Disorders in Pregnancy
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