R.G.
My family has a history of jacked up thyroids. With my 1st pregnancy my levels were borderline low and my doctor at the time said we could just watch it. We did, it was fine, baby was fine, no problems at all. I'm now pg with #2 baby and my new ob/gyn saw my levels and sent me to an endocrinologist (probably in my 2nd month of pregnancy) who put me on synthroid. I must say I think it has helped me not gain as much weight and I probably feel better from being on it. I will also have to continue taking it the rest of my life, which is fine. I don't know anything about having to be on it the first week for the baby's sake but I wasn't and neither of my children seem to be effected by that (although I haven't delivered yet, I don't expect any complications according to sono's etc.). I think it will be just fine for you, either way.
P.S. My endocrinologist firmly believes pregnant women need good thyroid levels but didn't seem too concerned that it was 2 months into my pregnancy that I got on medications. I hope that helps calm your fears. The internet can be a scary place!