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Worried about TSH level in pregnancy

I was diagnosed with under active thyroid 5 yrs ago and on 75mg levothyroxine since. I am now 29 weeks pregnant and my recent TSH has come back at 3.34 which I am worried is slightly too high. Can anyone tell me what the latest guidelines are? My GP is reluctant to increase my medication as I have had pregnancy related cardiology problems but am worried about the effects this result will have on the baby?

4 Replies


The foetus will be fine because it will have been independent of your thyroid hormone since 12 weeks. However, high TSH increases risks of miscarriage, premature delivery and post partum psychosis in the mother so your GP should increase dose to ensure TSH remains <3.0. Show GP the guideline below.

Management of primary hypothyroidism: statement by the British Thyroid Association Executive Committee

13. The serum TSH reference range in pregnancy is 0·4–2·5 mU/l in the first trimester and 0·4–3·0 mU/l in the second and third trimesters or should be based on the trimester-specific reference range for the population if available. These reference ranges should be achieved where possible with appropriate doses of L-T4 preconception and most importantly in the first trimester (1/++0). L-T4/L-T3 combination therapy is not recommended in pregnancy (1/+00).



Thank you for your reply! I will show him this, however I have recently had episodes of Sinus ventricular Tachycardia and he is concerned that increasing my dose will increase the risk of this happening again and feels that is the bigger issue. He has asked for my bloods to be repeated in 4 weeks. Is 3.34 significant enough to over ride my cardiac problem or will I be ok to wait till my next blood test?



It's possible your TSH 3.34 is causing the tachycardia. A dose increase of 25mcg isn't likely to suppress TSH below range. Suggest your GP consults a consultant endocrinologist if he still doesn't think dose should be increased after reading the BTA statement.


Ok thank you so much for your advice. I will contact him on Monday and suggest this.


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