Hi Evanna,
I was diagnosed with a complete placenta previa with my first child (I'm pregnant again, so you can tell I have a happy ending lol). Your 18-20 week appt is when they diagnose it anything earlier isn't accurate because early on, due to the size of your uterus (being small) every woman basically has one, or a low lying one. At 18-20 weeks it should have migrated, which really means it moves as the uterus grows, but doesn't "actually" move. For most women it ends up top of your uterus. Some of us, I have NO idea why (there are some lame statistics for why, but not one single one of them were true for me), it doesn't grow up with the uterus, it stays put. I was lucky and not lucky. I had some mild bleeding at 15 weeks before I ever had it diagnosed. It went away in a day and I never had a single day of bleeding after. My daughter grew perfectly well, no nutritional issues (as they can worry about because the placenta isn't located for optimal nutrition). I ended up with a partial placenta previa. It moved but not enough. So, I had a c-section. My section was without any issues. I didn't loose any extra blood, my placenta detached fine, I healed well. I, personally, think bedrest is a little overly conservative. Have you had any bleeding issues? My doctor put me on pelvic rest: no lifting, no sex (no orgasms), no exercise. He told me to put my feet up as much as possible and get a lot of fluids. I did all those things, and never had a day of trouble. So, fear not! You have every reason to hope for the best! I joined the yahoo chat group for placenta previa, and I read MANY encouraging stories. Now a days, they can totally deal with this, and they'll watch you and your baby very closely to make sure everything is okay. I was really scared at first too. All the internet stories terrified me. Just try to stay calm and not worry too much. If you have ANY contractions, call your doc asap. That is what they do not want to happen. But, in the meantime, just be gentle on your body and enjoy your pregnancy! Hang in there... :)