Thanks for all of your answers. Always good to know you aren't the only one with concerns.
arismomkoofie-- I'm not trying to talk you out of it, but apparently you can't tell much about placenta placement this early .. a lot of women have what looks like a low-lying placenta early on, but the problem goes away later on. what I would be nervous about is finding out that my placenta is borderline low (or some other questionable diagnosis), and then worrying about it for the whole pregnancy, ordering even more U/S, etc.
This Mothering article gives a good synopsis of the argument:
http://www.mothering.com/articles/pr...und-risks.html
It hasn't been demonstrated that ultrasound is definitely harmful, but it hasn't been shown to not be harmful, either. There really has not been enough research, IMO, to justify doing them routinely. Any technique that alters living tissue should be used sparingly, rather than as a matter of course.
As autumn_faune points out, they used to (as in, in my lifetime) x-ray to find out what was going on in there.
Anyhow-- I'm just discussing, not trying to be preachy. We all have to pick and choose and sometimes compromise on the gazillion issues that there are. I'm still drinking an 8 oz cup of coffee every morning, for instance ...