Pregnancy - TSH and FT4 levels

[svenena]

Background: early last year I had an episode of hyperthyroidism, followed by an episode of hypothyroidism, and then it went back to normal, within about six months. I didn't take any medication.

Then earlier this year I was diagnosed as hypothyroid, very early in my pregnancy (I'm currently about six months), and I was prescribed Levo. I'm currently taking 75cmg.

After an initial speedy drop, my TSH has continued to gradually reduce, so I'm expecting my dose will be reduced. But my FT4 is also continuing to very gradually fall, after an initial increase. Is that normal? I thought it would increase as TSH decreased, or is the correlation not that straightforward?

(nb I've removed some anomalous results because they were showing under the date they were ordered rather than when I actually had the test, several weeks later - they're in line with the other results though).

[greygoose]

As you are on levo, your FT4 level will rise or fall according to your dose, not the TSH. When on thyroid hormone replacement, the TSH follows the FT4 level, not the other way around. However, the TSH is slow to react and doesn't always keep up with the FT4 level - and there's also the FT3 level to consider.

So, if your doctor only looks at your TSH - which is 100% the wrong thing to do - and reduces your levo to try and get your TSH to rise (sigh), your FT4 will drop, and so will your fT3. Which is not what you want to happen. They are already too low, because you are under-medicated, despite the low TSH. So, refuse any attempt to reduce your dose. You need your Frees at least 50% through the range, if not higher. The TSH is the least important number.