Managing overt hypothyroidism in conception and pregnancy

What is overt hypothyroidism?

Overt hypothyroidism is defined as having a Thyroid Stimulating Hormone (TSH) greater than 10 mU/L with a free thyroxine (FT4) level below the reference range. 

What are the risks?

If it is untreated, or inadequately treated, it may be harder for you to become pregnant, and your pregnancy may be at higher risk. These risks include premature birth, low birth weight, pregnancy loss, and problems with your baby’s brain development.

How should it be treated?

Your doctor will give you levothyroxine treatment to try to bring your thyroid levels back into the normal range for pregnancy. This will give you the best chance of becoming pregnant, having a successful pregnancy and a healthy baby.


Before pregnancy

  • Your care will be managed by your GP.
  • Adjust your levothyroxine dose if needed to TSH <2.5 mlU/L.
  • Your thyroid function should ideally be checked every six months while trying to get pregnant.

During pregnancy

  • Double your levothyroxine dose on two days of the week as soon as you have a positive pregnancy test. Do not wait to see your doctor to do this.
  • See your GP to have your thyroid function test as soon as your pregnancy is confirmed, ideally by 7-9 weeks of your pregnancy.
  • Your TSH should be <2.5 mlU/L and your FT4 should be in the normal pregnancy-specific range.
  • Your GP should refer you to an endocrinologist/obstetrician.
          • Your thyroid function should be checked every 4 weeks until 20 weeks, then once again at 28 weeks.

After birth

  • Return to your pre-pregnancy levothyroxine dose 2 weeks after birth.
  • Get your thyroid function checked, usually during your 6 week postnatal check.

Note: If there are no pregnancy-specific ranges available, your doctor should use the TSH range 0.1-4.0mU/L.

Read the RCOG Green-top guideline on the Management of Thyroid Disorders in Pregnancy

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Author: Anna Woollven

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