M.M.
I had a low lying placenta at my 20 week US as well. Like everyone else has mentioned - mine moved by the time I had my next US (at 28 weeks). Don't stress about it too much (though I know that's easier said than done!). It's pretty rare for the placenta to not move by the time you're full term. And as someone else stated - you would just end up with a c-section, but at least you'll know about it in advance and it wouldn't be an emergency c-section. I've had sections with both my kids and, well, it is what it is. They're not all that bad.