Low t3, low t4 with normal tsh. Did it contribu... - Thyroid UK

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Low t3, low t4 with normal tsh. Did it contribute to miscarriage?


Hello, I'm a 31 year old female who recently has a miscarriage at 5 weeks. I am taking 25 mcg of t3. My last labs showed that I had a normal tsh with both low t3 and t4. I'm wondering if the factor of having low t3 and low t4 may have contributed to the miscarriage.

8 Replies

Hello amymimdes,

I welcome you to our forum and am so sorry to hear of your miscarriage.

A woman with untreated or mismanaged hypothyroidism is at greatest risk for a miscarriage during her first trimester.

When a woman is pregnant, her body needs enough thyroid hormone to support a developing fetus and her own expanded metabolic needs so low or unbalanced thyroid hormone levels may struggle to meet this demand.

Woman already medicating on Levothyroxine should discuss conception before with their GP & after be referred to a specialist.

It is usual to increase dose by 25-50 mcg Levothyroxine (after TSH testing) after conception.

TSH should be kept between the low-normal range (0.4 mU/L to 2.0 mU/L) and an FT4 concentration in the UPPER reference range. T3 is not usually measured.

Blood tests should be performed every four weeks during the first trimester, then 16 and 28 weeks of gestation, or more frequently if needed.




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Low T3 levels would also be a contributory factor in miscarriage and if you are medicating on T3 only, levels should be checked.

If your GP or endo is uncooperative, private testing may be obtained in link below..



I'm so sorry, Amy. Thyroid is very important for fertility as this short video explains. In fact, all other hormones may be affected as well. He explains many other symptoms as well.


Mary Shomon posts periodically about low thyroid and miscarriage. You might want to search thyroid.about.com for what she has said. For instance:


Also consider going to a bio identical doctor hence many women who tried bioidentical progesterone cream were able to successfully for the first time avoid miscarriage and monitoring their thyroid as well free t3 free t4 and .......I would definitely goolge that and read up on it

Something like one in four pregnancies end in miscarriage, so although there may have been a contributory factor, there equally may not be.

Are you taking separate T3 medication?

My Endo informed me that I would have to stop taking T3 during pregnancy as it can block the placenta of Thyroxine. A baby cannot produce its own until 16 weeks.

Yes I was taking T3 medication. I have now been taken off of it. Thank you for your reply!

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