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Thyroid UK
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T3 when ttc or in pregnancy

My latest bloods in May came back as the following:

TSH of 0.19 miu/L, free T4 19.4 pmol/L and free T3 low normal at 3.5 pmol/L.

The endo I am seeing at my request due to relatively low T3 advised that whilst there is a chance I'm not converting which the new blood test will highlight, he would not be keen to treat this as the jury is out in terms of risks when trying to have a baby (I am ttc currently).

Can anyone advise on this? If my T3 couldn't be treated wouldn't this put my baby (if I were to conceive) and me at risk?

6 Replies

Considering that T3 is the active hormone, I am not medically qualified to answer. This excerpt is from the following link with no mention of T3. My assumption is that they expect T4 to convert to sufficient T3:-

Using immunoassays the reference intervals for TSH in an iodine-sufficient population without any autoimmuno-antibodies are 0.24–2.99 mIU/L for the first trimester, 0.46–2.95 mIU/L for the second trimester, 0.43–2.78 mIU/L for the third trimester, while one year postpartum TSH reference interval for the same population was 0.28–2.94 mIU/L. The reference intervals for FT4 are 0.26–1.92 ng/dL (3.7–23.4 pmol/L) for the first trimester, 0.59–1.56 ng/dL (7.4–18.9 pmol/L) for the second trimester, 0.65–1.25 ng/dL (8.3–15.6 pmol/L) for the third trimester, while one year postpartum FT4 reference interval for the same population was 0.77–2.26 ng/dL (9.9–28.4 pmol/L).


However, I think I'd pay more notice to the info on this link:-




If FT3 is 3.5 you are converting, just not very well. The British Thyroid Association isn't keen on T4+T3 combination treatment and doesn't recommend it for pregnant women. Members have taken T4+T3 throughout pregnancy and I think one or two may have taken T3 only during pregnancy. There doesn't appear to be evidenced based research into safety of taking T3 during pregnancy (which doesn't mean it is unsafe) so doctors will usually try to persuade pregnant women to take Levothyroxine only until after delivery.


Sorry Clutter I meant to reply to you directly but have added the post with questions below now (still getting to grips with the forum).




Thanks Clutter. Is there a risk to the baby if I'm NOT taking T3? Is there a lower chance of conceiving if my T3 is marginal or failing?



If there was a risk to the foetus by not taking T3 BTA wouldn't recommend Levothyroxine only. I don't know whether low T3 affects conception.


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