Thyroid hormone replacement in pregnancy t4 onl... - Thyroid UK

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Thyroid hormone replacement in pregnancy t4 only or combination?

trucall profile image

I am seeking advice. For the last few years we have been trying to conceive whilst also battling with hypothyroidism. T4 alone (200mcg) just didn't work for me. After fighting for the t3t4 combination (t3, 5mcg twice day, t4 150mcg) things started to get better relatively speaking. At least bloods are in normal range with TSH suppressed. The advice up to yesterday had been that on positive pregnancy test increase my t4 intake. However, yesterday I updated my consultant that now I managed to get my weight down we can progress with IVF next month. I was told to stop T3 immediately and increase t4 by 25mcg to 175 MCG on positive test after implantation (fyi this would take me to a lower level than when I was previously on t4 alone). The only reason they gave was that they have no evidence on how to treat with T3 during pregnancy. I found this shocking and very confusing. Could I request people to get in touch if have experience of taking t3t4 (leothyronine and levo not thyroid extract) during pregnancy. Or if you have info / evidence of risk, benefits of changing from my adequate regimine to one that previously hadn't worked. Including risk to fertility, success of IVF and risk to pregnancy and embryo development +/- T3. Many thanks.

7 Replies

I wish I could help here but I’m out of my depth. What I did during pregnancy was take only Levothyroxine. I took no T3. However, my Levo dose was only 50mcg. So my thyroid issues are not as bad as yours and maybe this allowed me to take only T4.

I hope you get answers.

Hi there and firstly very best wishes for your IVF. I am starting my second round next month.

I don’t have any definitive advice for you but I am on T3 only (I have a conversion problem) and my endo Was very clear that it would be very damaging to stop T3 during pregnancy and I may need to increase it.

My IVF Doctor has queried whether I also need to add some T4 so that the baby would have access to it in the first trimester before the placenta starts making its own. Apparently T4 is what crosses the placenta and my T4 is suppressed as I am on T3 only. I am waiting for an opinion from my endo on this to see what meds I need.

It isn’t simple and I wish you the very best of luck


I do know someone who you could speak to. I will message you

SuzelleG profile image
SuzelleG in reply to Chippysue

Hi chippysue, can you send me some info on this please? Many thanks.

My husband and I want to try soon and so I switched from combo to t4 to see if I could cope. I couldn't long story short. T3 is licenced for pregnancy and they don't have a lot of research to help them interpret the bloods. I was told that whilst it is not preferred to be on combo it is possible.

Risks I was told about where that there maybe an increases risk of miscarriage, also it may affect the baby's IQ as t3 hormone struggles to get from mum to baby.

My personal argument to this was that I felt so aweful on t4 alone I couldn't see how I could carry a pregnancy.

Good luck.

My endocrinologist advised against taking T3 during pregnancy and suggested it would be dangerous developmentally for the developing baby. I looked into it a little bit and there are no clear studies on the safety of using it during pregnancy.I am on Levothyroxine 125mg and will see the endo next month before a frozen embryo transfer. Good luck.

Thanks for all the replies. What I gather is the free t4 has to be sufficient for myself and baby. As to T3 supplement that is unlikely to help baby because doesn't cross placenta like t4. But if it helps me what are the risks? Sounds like the risks are associated with not enough t4 for baby rather than T3 being detrimental.

My assumption is that if all levels TSH, ft4 and ft3 remain in recommended range for each trimester it is equivalent to a non supplemented healthy person and would be the best case scenario. What am I missing?

Is the T3 replacement somehow more harmful than what healthy individuals would produce naturally?

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