T3 in Pregnancy and breast feeding

[Jools21]

I am trying to assist a friend late 30’s who is now about 17 weeks pregnant. She has been on a combination of Levothyroxine and Liothyronine for many years and has been well. Her drs have stopped the Liothyronine and upped her Levothyroxine, informing her Liothyronine is not licenced in pregnancy so she cannot have. (Is this really the case?)

Both of us can find no evidence that says that Liothyronine is unsafe in pregnancy or whilst breastfeeding. She wishes to breast feed and has been told no Liothyronine until she stops breastfeeding.

As she has a clear physical need for Liothyronine, then this need surely does not suddenly change. My research so far has found that the body needs more thyroid treatment in pregnancy.

If anybody can help point me in right direction or any information would be much appreciated as she wishes to have her Liothyronine reinstated now not in 1-2years time.

Thank you

[FallingInReverse]

This article is relevant, although probably wouldn’t convince the NHS.

But it’s good info on the knowns/unknowns of the risk.

drugs.com/pregnancy/liothyr...

[Jools21 in reply to FallingInReverse]

Thank you very much. It’s good to know as much as possible

[HealthStarDust]

I know it’s not ideal, but she can get T3 from privately straight from pharmacies such as Roseway labs. I am unsure why T3 isn’t recommended during pregnancy as I am not sure how it would cross the placenta.

I can say, it is very unlikely for someone in the NHS to prescribe liothyronine during pregnancy.

[Jools21 in reply to HealthStarDust]

Thank you. So I am assuming she will need a friendly private Dr who is happy to prescribe.

[Watamu]

contact La leche league, this is the best breastfeeding support group, they may have members with the same issues

[Jools21 in reply to Watamu]

Thank you. I will look up the La Leche League. It’s good to know there is support out there.

[humanbean]

These could be printed out and shown to a doctor :

endocrine-abstracts.org/ea/...

endocrine-abstracts.org/ea/...

...

The medical belief that T3 doesn't cross the placenta doesn't stack up logically because :

1) Approx half way through pregnancy the fetus's thyroid, pituitary, and hypothalamus are quite well developed. (The pituitary and hypothalamus control how much thyroid hormones the thyroid will produce.) As a result the fetus relies less and less on the mother's thyroid hormones and instead makes their own.

If you want chapter and verse on fetal development of the thyroid this link gives you everything you need to know. Just reading the Introduction is probably enough to get the gist.

embryology.med.unsw.edu.au/...

2) Everyone, male and female, at every age, produces T3. It is the active thyroid hormone. This will apply to the fetus too, once it is well enough developed, but before that it must rely on the mother. I have read that doctors believe the placenta converts T4 into T3. I haven't researched this, but it might be worth checking.

3) Low T3 syndrome is known to be fatal if it is bad enough - see this paper with a very scary title. Doctors assume that low T3 isn't a problem for fetuses but are too scared of T3 to even research it in pregnancy, as far as I can tell :

ahajournals.org/doi/10.1161...

3) Beliefs about the placenta not allowing T3 to pass from the mother to the fetus appear to be mostly based on the study of placentas after they are ejected after birth. There will be little or no T3 in a placenta because by the time a fetus is about to be born they are making their own T3. If they got T3 from the mother as well it would make the fetus hyperthyroid.