I second everything scout 8601 said. I had missed mc all tests will come back positive until u pass everything. I was same way had 3 miscarriages the last one a missed one. Had tests done after the 3rd, nothing wrong with me. I am now 22 weeks, so far so good (knock on wood). Everyday is a miracle to me. I still look for blood when I potty, can't help it. But I still pray for thanks she's hanging in there and pray for the next.
I am going in for weekly injections of hydroxyprogesterone to help me make it to term. A precaution since my son was premature (born at 33 weeks, hes 10 now) and with the 3 m/c in a 14 month span starting in July '10.
Good luck. Keep us updated.
First, I'm sorry for your m/c's. I know how devestating they are. As to your question, I believe if it's a missed m/c you'd still have positive pregnancy tests until everyitng is expelled and all the hcg is gone. I know with mine, I do think the hcg dropped a good bit bc my pregnancy symptoms lessened, but it wasn't unitl after the D&C that the level got back to 0.
Good luck, hun. I know you are scared, but there is a really good chance that this pregnancy will be just fine. Waiting is awful, tho, right?? I wish you all the best and I'l like to say try to relax and not worry, but since I've been there I know that's not going to happen. Just take it one day at a time and I always liked the saying, 'cautiously optomistic'.