This is a paper that supports everything I have ever written on the safe experience women have had throughout pregnancy when on T3-Only replacement therapy.
It is consistent with the information I provide in Chapter 18 (the T3 Treatment chapter) on page 147 of The Thyroid Patient’s Manual.
Here is the research article:
“Normal neurodevelopment of children from a mother treated with only Liothyronine (T3) during pregnancy – a case report”
Sidrah Khan & Trevor Wheatley
Endocrine Abstracts (2016) 44 EP105
DOI: 10.1530/endoabs.44.EP105E
https://www.endocrine-abstracts.org/ea/0044/ea0044EP105
The woman concerned had very low FT4 during her pregnancy but there were no developmental issues with the foetus or baby.
This paper shows that T3 must indeed cross the placenta and provides the foetus with adequate thyroid hormone until after 20 weeks when it is self-sustaining.
One further, research paper dating back to 2006 also shows that T3 and T4 both cross the placenta via the MCT8 transporter throughout pregnancy. I will provide a link to the abstract and the full paper below. However, the evidence is there from practical experience and research that T3 does indeed cross the placenta during pregnancy, i.e. those women on T3-Only or T3-Mostly do not have to reduce or stop their T3 and replace it with T4 medication.
Here is the abstract followed by the link to the full paper:
https://pubmed.ncbi.nlm.nih.gov/16731778/
https://joe.bioscientifica.com/view/journals/joe/189/3/1890465.xml
It supports what I have been saying for many years about the misinformation and twisting of small pieces of research that often leads to people being frightened of T3-Only therapy.
There is no need to be frightened, as T3-Only therapy (if it is required) does replace the function of T4 without any adverse consequences. There is plenty of other anecdotal evidence of other women who have had successful pregnancies using T3-Only throughout the entire time from conception to birth.
Dr John C. Lowe also had many women patients who had successful pregnancies whilst on T3-Only.
Over the past ten years, there have been doctors and patients who have argued that only T4 can cross certain systems. The blood-brain barrier and central nervous system were being mentioned for a long time, as areas that only T4 could access. This has been shown to be totally false due to the discovery of active transporters:
https://paulrobinsonthyroid.com/t4-is-not-needed-in-the-brain-in-adults-research/
I believe any other claims that T3 cannot replace the function of T4 will also be proven in time to be false. There is already enough evidence from people who live healthy lives over many years on T3-Only that I am certain of this.
As I mention on page 147 of The Thyroid Patient’s Manual, anyone who is still concerned about needing some T4 could take some during the first 20 weeks of pregnancy, after that time the foetus is self-sustaining with its own thyroid hormones. The foetus begins to make its own thyroid hormones after 12 weeks but doesn’t need any at all from the mother after 18-20 weeks. However, T4 is really not needed, as from practical experience of women who take T3 only, the T3 must cross the placenta during the early stages of pregnancy.
Best wishes,
Paul
