On the right you'll find a link to download the PDF. Scroll down to page 1206 and you'll find a beautiful chart laying out a ton of studies testing the impact of ultrasound. You'll notice the few who didn't have "no association" only had lower birth weights and only with the babies exposed to an abnormal amount of US.
There's also this: http://onlinelibrary.wiley.com.library.smu.ca:2048/doi/10.1002/uog.6328/abstract;jsessionid=72767534141D93EC251074DEE6A8F3A7.d01t03?systemMessage=Wiley+Online+Library+will+be+disrupted+on+15+September+from+10%3A00-12%3A00+BST+%2805%3A00-07%3A00+EDT%29+for+essential+maintenance
I adore because it lays out all of the potential areas that could be impacted, then summarizes the results of the various studies included in the 61 study meta-analysis. According to this, ultrasound doesn't really have an impact and in the few instances it might, the chances are so low (around .5%) that it's more dangerous for you to cross a street than to get an ultrasound in terms of potential for something to go wrong. There might be a chance your baby could be slightly more inclined to be left-handed if it's a boy as well. Oh no. The horror.
I've been researching this for an hour or so and using my connections through work to do so, so I"m not sure you all will be able to access them for free. If not, here are the proper references:
Houston, L. E., Odibo, A. O., & Macones, G.A. (2009). The safety of obstetrical ultrasound: A review. Prenatal Diagnosis, 29(13), 1204-1212.
Torloni, M. R., Vedmedovska, N., Merialdi, M., Betrán, A. P., Allen, R., González, R., Platt, L. D. (2009). Safety of ultrasonography in pregnancy: WHO systematic review of the literature and meta-analysis. Ultrasound in Obstetrics & Gynecology, 33(5), 599-608.
You can also contact me and I'll send you a PDF copy of each article.
I also agree completely about the psychological impact of ultrasound for reassurance in mothers who have had losses previously, and even for those who are more prone to worry. The benefits greatly outweigh the risks.