Because if a woman struggles to produce thyroid hormones in the first place, and she is providing sustenance to a hungry infant her thyroid hormones may struggle to keep up.

I would have compared feeding an infant when the mother has thyroid disease to being akin to exercising a lot with thyroid disease or dieting a lot with thyroid disease, and I wouldn't think either of those two things were a good idea for many of us.

Maybe I just have a woolly idea about the strain that breastfeeding has on the body. I've never had any offspring so breastfeeding is a bit of a black art as far as I'm concerned.

Hormones are very different for breastfeeding women - it alters hormones in a big way but less than pregnancy itself and the menopause. For example, that's why some (not all) women don't get periods back until they stop breastfeeding.

Also, a lot of vitamins and minerals go from the mother into the milk. The iodine required by a breastfeeding woman is extremely high as breastmilk is so high in iodine. It just makes me wonder how it affects thyroid function and therefore how it will affect my thyroid function test results.