TSH Levels in Pregnancy Chart & Levothyroxine Dosage Calculator

TSH Interpreter

Check if your thyroid levels are normal for pregnancy

Pregnancy Stage

Your TSH Level

mIU/L

Current Weight (Optional)

Used to estimate dosage if needed.

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Normal Ranges (ATA Guidelines)

TTC / Non-Pregnant 0.4 – 2.5 mIU/L

First Trimester 0.1 – 2.5 mIU/L

Second Trimester 0.2 – 3.0 mIU/L

Third Trimester 0.3 – 3.0 mIU/L

Levothyroxine Dosage Estimate

* This tool is for informational purposes only. Dosage estimates are based on the American Thyroid Association (ATA) 2017 Guidelines for calculating full replacement doses (1.6mcg/kg) vs starting doses. Always consult your endocrinologist before changing medication.

Peer-Reviewed Science

Updated Dec 2025

See Methodology

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Normal TSH Levels in Pregnancy Chart

During pregnancy, your body requires more thyroid hormone to support the developing baby. As a result, the "normal" range for TSH (Thyroid Stimulating Hormone) is strictly lower than for non-pregnant adults. Most guidelines, including the American Thyroid Association (ATA), recommend the following upper limits:

Trimester	Reference Range (mIU/L)
First Trimester (Weeks 1–12)	0.1 – 2.5 mIU/L
Second Trimester (Weeks 13–26)	0.2 – 3.0 mIU/L
Third Trimester (Weeks 27–40)	0.3 – 3.0 mIU/L

Note: Some labs use a universal upper limit of 4.0 mIU/L. However, for fertility and pregnancy safety, many endocrinologists prefer the stricter cutoff of 2.5 mIU/L to minimize miscarriage risk.

Levothyroxine Dosage Chart (Hypothyroidism)

If your TSH is elevated (Hypothyroidism), your doctor may prescribe Levothyroxine (synthetic T4) to bring your levels down quickly. The starting dose depends on how high your TSH is and your current body weight.

Below is a general dosage chart based on clinical guidelines for starting doses:

Condition	TSH Level	Typical Starting Dose
Subclinical Hypothyroidism	2.5 – 10 mIU/L	25 – 50 mcg
Overt Hypothyroidism	> 10 mIU/L	Full replacement (~1.6 mcg/kg)
Known Thyroid Disease	Already on Meds	Increase dose by ~30% immediately

How is "Full Replacement" Calculated?

For women with overt hypothyroidism (TSH > 10) or those who have had their thyroid removed, the dose is calculated by weight:

Daily Dose = 1.6 mcg x Body Weight (kg)

For example, a woman weighing 70kg would require approx 112 mcg daily.

Important Safety Note: Never adjust your thyroid medication without a blood test and doctor's approval. Taking too much Levothyroxine can cause Hyperthyroidism (Low TSH), which carries its own risks for the baby, including fast heart rate and growth restriction.

Frequently Asked Questions

What causes High TSH in pregnancy?

High TSH indicates your thyroid is underactive (Hypothyroidism). In pregnancy, your thyroid must work 50% harder to produce hormones for both you and the baby. If it cannot keep up, your pituitary gland screams "Work Harder!" by releasing more TSH.

Is a TSH of 3.5 dangerous?

A TSH of 3.5 is considered "normal" for a non-pregnant adult, but it is elevated for the First Trimester (where the goal is < 2.5). While not an emergency, doctors often treat this "Subclinical" elevation with a low dose of medication (e.g., 25mcg) to protect the pregnancy from potential miscarriage risks.

Methodology: How this works

1. Reference Ranges (The "Traffic Light" Logic)

This calculator compares your input TSH value against trimester-specific cutoffs defined by the American Thyroid Association (ATA) 2017 Guidelines. Unlike standard lab reports which often use a generic "non-pregnant" upper limit of 4.0–5.0 mIU/L, this tool applies the stricter pregnancy thresholds:

First Trimester: Strict cutoff of 2.5 mIU/L. Values between 2.5–4.0 are flagged as "Subclinical" risk zones.
Second & Third Trimesters: Relaxed cutoff of 3.0 mIU/L as the hCG effect wears off.

2. Dosage Estimation Algorithm

If your TSH is flagged as "High" (Hypothyroid), the tool estimates a starting dose of Levothyroxine (T4) using two clinical pathways:

For Mild Elevations (TSH 2.5–10): The tool suggests a conservative starting dose (typically 25–50 mcg) to avoid over-correction (Hyperthyroidism).
For Overt Elevations (TSH > 10): The tool switches to a "Full Replacement" calculation based on body weight, as recommended for patients with little to no thyroid function.

Full Replacement Dose = 1.6 mcg × Weight (kg)

Note: If you enter your weight in pounds (lbs), the calculator automatically divides by 2.20462 to convert to kilograms before running the formula.

Scientific References & Guidelines

American Thyroid Association (ATA): 2017 Guidelines of the American Thyroid Association for the Diagnosis and Management of Thyroid Disease During Pregnancy and the Postpartum. (Primary source for TSH cutoffs and dosage calculations).
The Endocrine Society: Management of Thyroid Dysfunction during Pregnancy and Postpartum.
National Institutes of Health (NIH): Subclinical Hypothyroidism in Pregnancy: Clinical Implications and Management.
UpToDate: Hypothyroidism during pregnancy: Clinical manifestations, diagnosis, and treatment.