Thyroid UK

3rd trimester TSH too low

Hi all. You've helped me before. This time at 28 weeks my tsh was 0.05. I was taking 150mcg levothyroxine. Pre-pregnancy dose was 100mcg. I'm now 30.5 weeks and still awaiting a call from endo. Despite chasing midwife who's refaxed referral. Is it likely my dose will go down or do you need t3 and t4 results to be able to tell me? Thank you. GP got it wrong at 16 weeks and told me to reduce. 1 week later midwife called to say endo advised staying on 150.

3 Replies

Tsh of 0.05 is fine and anyone who wants it higher is criminal

its vital for the baby that you have enough thyroxine in the body although t3 is of course the vital thing

on no account let them reduce your dosage


Your baby starts to produce its own hormone after 12 weeks, so by now it is looking after itself thyroid wise.

A TSH of 0.05 is rather low. Although I don't think it will present any significant risk to the baby from your own point of view I would decrease your levothyroxine dose a little (provided your fT4 level is OK). The reason is that when our TSH is suppressed for some time (or near suppressed) the 'hypothalamic pituitary thyroid axis' can become down-regulated. You produce less TSH than you should do and this has knock on effects on your ability to convert T4 to T3. So if I were in your shoes I would adjust my dose to keep my TSH between 0.5 and 2.5. After the birth you will probably go back to your original 100 mcg dose.

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Well, you have two differing opinions, there. Myself, I would say, get your Frees tested before changing anything. :)

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