Hi second all of the above. The studies that show issues for baby are with very undertreated or subclinical (not treated) Hypothyroidism and in parts of the world where there is little or no iodine in the diet. We need a little more in pregnancy than usual, this is easily found in three good serving of dairy (fat free or full fat, makes no difference) each day.
I recently went to a British thyroid meeting run by a consultant obstetrician.who had special interest in this. She personally would like women to up their dose them selves (by 30 to 50%) on bpf. I found this an extra worry till docs got my bpf confirmed and agreed though erred on side of caution. I've had a strangely rocky ride (went quite under despite 2 early raises) but possibly due to being on a brand that was withdrawn (teva) in march/april. I've since gone over a bit since a panicked consultant wacked me up to 225 (tsh was 11, now 0.05, t4 20) but that is fine for a short while. Patients pregnant with thyroid tumours are completely suppressed.
She also recommended pregnacare which has the 3 main vital vits; folic acid, iodine and vit d. It's not the full dose of iodine needed as too much is not recommended but too much would actually be quite a lot of yoghurt!
Iodine is used to convert t4 (thyroxine) into t3 which the cells use. Baby needs t4 from mother. He makes his own around 26 weeks but continues to rely on mums till birth.
I've not had very consistent care (latest eg: last doc at hospital, an SHO or JHO, didn't have a clue about pregnancy ranges minipie has detailed and kept running off to her consultant) and a gp admitted they are having a problem with the labs. Frequently the docs request for t4 was ignored, you must make sure you have both t4 and tsh. I've learnt you must ask the nurse to write pregnant and how many weeks on the blood bag too. Find out results too, it can help to keep track. I must admit I've booked blood tests roughly each 3 weeks following the crazyness, and my gp actually thought the hospital said each 2 weeks.
Personally next time I will up it myself.3 different gps gave diff advice pre preg and then in early preg and I've been to hell and back with the stress of it all.(also due to actual effects of fluctuating thyroid plus slapped cheek issues but that's another story!) I now know everything will be ok but had to do a lot of finding out till finally saw consultant at 13 weeks. The British thyroid foundation are excellent and supported by the British thyroid association, the UK's expert endos. There are bits of info in their newsletters. Midwives don't know anything though apparently the top endo here did send out a fact sheet to them all.
Need to emphasise mine has reacted strangely and if you don't have a thyroid it should be easier to control but you actually have a right to be referred to an endocrinologist or obstetrician now to check.all these things (as 2 consultants have emphasised now).
All the best! Xx