Dosage matters, that is for sure. Difficult to say if I ever will be able to not take iodine; been there 2 years now, will do another year and see. I did try lower dosage this autumn, it was no success.
As long as we have the burden of fluoride, bromide etc I believe we need Iodine to counteract their destructive effects.
I would, if I was hypo T; address this before a pregnancy. Give it a year or two if you can afford to wait; it takes time to cure hypo T; it took me well over a year before I was considerably better!
When addressed it might be possible to go through pregnancy with "just" kelp and a lower dosage of iodine.
I periodically take kelp myself; not as my Iodine supplement but as a supplement to my iodine;
due to its high content of minerals and trace elements.