Hi,
Just thought I'd add my experience, although I'm no expert. But when I was thinking about TTC, I wanted all the information I could get my hands on!
Firstly, I was diagnosed with hypothyroidism over seventeen years ago. (I was only seven, so very young!) I've been on thyroxin ever since, and the dose has been stable for as long as I remember - certainly over ten years. However, although my thyroid was well controlled, I did have very irregular (anything between 19 and 49 day!) periods, which was a worry.
Before starting to TTC, like you, I read a lot, and scared myself senseless! Fortunately though, I fell pregnant in my third cycle. Spent an absolute fortune on HPTs, because I wanted to make sure I found out asap, so that I could get to the doctor asap!
When I got my BFP, I was in two minds about whether or not to up my dose of thyroxin before seeing the doctor. (Most of what I read seemed to be suggesting that you take an extra 50% of your regular dose, asap.) However, I held off and saw the doctor within a couple of days. He was great. Took blood and sent it off to be tested urgently. However, he did advise me, to my surprise, to stay on the dose of thyroxin that I was on until the results were back. His reasoning was that the effects of a new dose don't kick in for 6-8wks, and waiting 48hrs for the results wasn't long in comparison. And there was a chance that I mightn't need my dose upped, in which case I'd be messing with an already stable dose for no reason. Sounded quite logical to me.
Anyway, when the results came back (within 36hrs), he phoned me. My TS3 and TS4 levels were alright, but TSH was way off, so I did need a higher dose. I was put on that immediately, and advised to have my levels tested again 6wks later. That was Tuesday, so I won't get the results now until later this afternoon.
Now for the pregnancy itself... I've been told I did well to get pregnant as quickly as I did (three months). But then that's not bad even if you haven't got an underactive thyroid. I have felt absolutely exhausted since getting pregnant (don't thinkk I mentioned I'm currently 12wks). Tiredness is a symptom of both pregnancy and hypothyroidism, so I'm not sure of the exact cause of mine - maybe it was a bit of both? Aside from that, I've also hadd very severe morning sickness. (All day sickness.) I've been hospitalised twice in order to be treated for dehydration. Apparently (unfortunately) this is very common in hypothyroid mums-to-be. But hopefully it'll ease up soon, as the placenta takes over and as my thyroxin dose stabilises again.
The other impact of hypothyroidism is that I have to have consultant-led care, rather than midwife-led. To be honest though, I'm fine with that. It's nice to think I'm in the safest of hands.
Risk of miscarriage was certainly higher because of my thyroid, but, now that I've had my 12wk scan, my consultant has said that he's not overly concerned about me. Yes, my risk is still higher than other women's, but I don't drink, don't smoke, am a normal weight and am young (24), so all of these factors lower my risk and overall, I'm not THAT much more likely to miscarry any more than any other woman would be.
So I don't know your situation but maybe cutting out alcohol, cigarettes and eating healthily would be a good idea? (If you haven't already done this!)
I had read about potential trouble with breastfeeding, and questioned my consultant about it on Tuesday, but he seemed to think it was best not to worry too soon. That, up to now, I've had no problems (aside from sickness, which is bad for me but fine for the baby). He assured my that my thyroid would be well monitored throughout my pregnancy. He said I shouldn't be concerned if I end up on three or more times my original dose by the end. But that once the baby's born, I'll need less again, and that'll all be monitored. He reckoned that with careful control, there's no reason I won't be able to try to breastfeed.
This is a LONG post! Hope it was interesting for you though, and not just too much information!
Good luck though!