I'm going to do the counter-culture thing ...
PLEASE check out autism rates in technological countries, and how they are directly related to socialization of medicine (therefore greater proportion of prenatal ultrasound) ... the semi-panic from the OB's and pediatricians when the mall-ultrasound picture-shops went in ... the increases in autism, heart defects, and genital defects that are time-correspondent to use of prenatal ultrasound (where are the areas we most focus ultrasounds?) ... the descriptions of ultrasound procedures used on adults (example, kidney stone destruction) ... types of heat caused by ultrasound in tissues (bone retains heat longer) ... Summer 2006 saw studies published (in the Associated Press!!) that in mice prenatal ultrasound exposure was directly proportional to the specific types of neurological damage associated with autism in humans ...
remember that OBs told women in the 70's that prenatal x-rays were safe
know that the medical guidelines in America have ALWAYS been that it shouldn't be used prenatally beyond diagnostic purposes (they reiterated that when the mall shops happened)
and know, that the "doppler" heartbeat-listener is louder and more focussed than the picture machines ... and birth-monitors (those belly-straps) are also ultrasound now ...
if you choose to listen to these ideas, you will have a hard fight ahead of you
with autism in my family, it was a fight I fought, even before the research started to come out supporting my instinctive, intuitive distrust of ultrasound (I had the first OB ultrasound my hand with the Dopp-Tone ... I felt it get warmer, inside, and never accepted the Dopp-Tone again) ...
I am totally totally sorry to be a downer. Once one starts looking, the evidence is stacking up pretty clearly, though :(, and since you haven't yet gone in (so I'm not guilting you, just offering an alternative way of considering the decision), I felt it incumbent to speak ... : ( ...