I did with DD because I had had a m/c right before I fell pregnant with her and I felt like I needed some kind of information to make me feel everything was ok in there! But this time I didn't. I didn't see the point, I felt that if something was going to go wrong then I unfortunately couldn't do anything about it.
This is where I am at too. It doesn't change the outcome but gives me another thing to stress about. I think I'm going to just cross fingers and toes and wait til the 8 week scan (or 7 weeks if I can't wait that long LOL). Hypothetically of course.