Thyroid UK

Low tsh levels in pregnancy

Hey, I am currently 4 weeks pregnant with my second. I developed thyroiditis during my first pregnancy which was detected a few months after giving birth. I was originally overactive but then it turned into underactive and I've been on thyroxine for about 18 months

I had a routine thyroid check a few weeks ago (before pregnant) and my tsh level had dropped to 0.47 which is at the low end of the normal range

My doc told me to have another test soon as I fell pregnant which I had 2 days ago. Just discovered my tsh is now 0.05 which is lower than normal range. My doc says this suggests I need to reduce my thyroxine amount but isn't going to do anything yet and wants me to have another blood test in 3 weeks

Is this ok? I am worried that by having a low tsh level it could effect my pregnancy?

Anyone have a have experience of this- ive heard of tsh levels increasing in pregnancy and therefore needing more thyroxine but not the other way round

6 Replies

Helen2407, Congratulations on your pregnancy.

NICE CKS recommends the TSH of pregnant women should be in the low normal range 0.4-2.0 with FT4 in the upper quadrant of range. The foetus is entirely dependant on maternal hormone during the first trimester and this is probably why your GP hasn't reduced dose yet as TSH will probably rise.

TSH 0.05 is low, but not suppressed and I don't think you should worry because your GP is monitoring you closely and will reduce your dose if TSH doesn't rise. I do think FT4 should be requested at the next blood draw. Leave 24 hours between last dose and blood draw as Levothyroxine can peak in the blood for up to six hours after last dose.

1 like

Like Clutter says it just needs keeping an eye on - it is not supressed. Do you feel OK? I had a very similar story to you. Thyroid problems diagnosed after first pregnancy, over then under. I had a second pregnancy with no complications and didn't need to change my thyroxine dose during pregnancy - just had regular blood tests to keep and eye on it.


Hi, thanks so much to both of you for replying to my post. Makes me feel better :)

I've got a Dr appointment later on today just so I can double check it all and I'll ask bout my t4 and t3 levels too

One other thing- I've been taking folic acid since trying to conceive but the midwife told me this week I need to take Vit D too. So I bought a pregnancy vitamin but it has other things in too like iron and read somewhere you have to be careful with iron tablets when you are on thyroxine. Have either of you heard this?


Not heard that - I just took a pregnancy multi vitamin and my thyroxin and that was all.


Hey just been to docs and he has said its fine to wait for 3 weeks until my next blood test and has put my mind at ease a bit

I asked about my t3 and t4 and my t4 is 24.4 and my t3 was 5


TSH is not enough to determine your thyroid status, especially when already on meds. You should get a ft4 and ft3 as well, especially important since another live is depending on proper thyroid levels. I would be afraid of a doctor who says what yours did and find a specialist, someone who knows thyroid and how to treat it. Miscarriages are common with people that are hypothyroid and have hashimotos.


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