Log in
Thyroid UK
91,937 members106,200 posts

29 weeks pregnant Hashimoto's but strange thyroid results

Hi - I'm 29 weeks pregnant and wondered if anyone might be able to help shed any light on my strange thyroid blood test results please. I have great trouble taking levothyroxine because of suspected intolerance to the fillers in the tablets and equally had trouble taking a liquid form, however I have a wonderful endocrinologist and GP and am now taking Tirosint which is sourced from the US. I have a low BMI generally and few symptoms of hypothyroidism and for the first part of my pregnancy I was taking only 25 micrograms every other day of levothyroxine, although this was increased two months ago to 25 micrograms per day. My free T4 has gradually been falling and is now just under 10, but my TSH has also been decreasing and has gone from 3.2 to 1.7 over the past months. My free T3 has hovered around 3.5 but since increasing my dosage has suddenly leapt from 3.5 to 5.6 in only 6 weeks. I seem to be very sensitive to dose changes and have been in the past but as I'm pregnant at the moment I'm particularly anxious about the results given my free T4 is still travelling downwards, which would imply my Tirosint needs increasing, and yet the free T3 has suddenly shot up. I do have a brilliant endocrinologist but he is away at the moment and I would be grateful to know if anyone else has been in this situation or can shed any light on this situation for me please. I also have a constant dilemma of whether to take iodine given I have Hashimoto's, I know the baby needs iodine (and I am intolerant to eggs and lactose, as well as now being coeliac as of last year when I was very poorly) but read so many contradictory reports. Thank you.

4 Replies

HelsS, It is unusual for TSH and FT4 to drop. TSH will drop in response to rising T4 and T3 when sufficient circulating hormone is detected and FT3 5.6 in a range topping off at 6-7 is very good. Improved T4 to T3 conversion which has made your FT3 rise from 3.5 to 5.6 may be why FT4 has dropped. The other possibility is that you had a Hashimoto's flare up which causes thyroid cells to dump hormone into the blood as they die off and may have caused high FT3 when you were tested.

The baby will have developed his/her thyroid gland at 12 weeks and will be independent of maternal thyroid hormone.

There is iodine in thyroid replacement which with diet should make iodine supplementation unnecessary. Iodine supplementation is contra-indicated in Hashimoto's patients as it can trigger flare ups. As you are intolerant to lactose and eggs you should eat plenty of other iodine rich foods.


I am not a medical professional and this information is not intended to be a substitute for medical guidance from your own doctor. Please check with your personal physician before applying any of these suggestions.


Thank you for getting back to me that's a great help. The lab range for FT3 for my specific lab is apparently 3-5 which is why I was really worried about the FT3 having shot up out of range also. You mention that thyroid replacement contains iodine, is that correct? My multivitamins are wholefood based and do contain some iodine, whether that has had an effect I'm not sure, and I do have some Lugol's iodine as I was conscious that I must have been iodine deficient but I think it's sensible to avoid taking this whilst pregnant? Thank you again.


HelsS, FT3 5.6 is mildly over range and won't harm you. It's FT3 considerably over range for long periods which may cause long term adverse effects.

You're taking a low dose of Tirosint so there won't be much iodine in it and the iodine in a multi-vit in addition to diet should be helpful. The RDA (maximum) of iodine from supplements and diet is 150mcg. I don't know how much, or whether, iodine should be taken during pregnancy. I'm just aware that high dose iodine can trigger Hashimoto's and increase Hashi flare ups.


I am not a medical professional and this information is not intended to be a substitute for medical guidance from your own doctor. Please check with your personal physician before applying any of these suggestions.


Thank you, it's a relief to know the FT3 won't have any adverse effects, and given my FT4 I feel as though I should be increasing the Tirosint really but I will see what my endocrinologist thinks. I know that in terms of the baby's development iodine is critical which is why I've felt I've been caught a little between a rock and a hard place so to speak, but hopefully the iodine in the supplement is at a level which benefits the baby without causing Hashimoto's flare ups or thyroid issues. I do also take zinc and selenium as I think if those minerals are at a healthy level the body can better cope with iodine, or at least I think I read that! Thank you again.


You may also like...